Android Development


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Android Development

  1. 1. Home Tutorials Trainings Books Connect Android Development Tutorial Based on Android 4.0 Lars Vogel Version 10.3 by Lars Vogel Copyright © 2009, 2010, 2011, 2012 Lars VogelTutorial 17.04.2012 Android Training 2.8k Revision History Revision 0.1 04.07.2009 Eclipse Training Created Revision 0.2 - 10.3 07.07.2009 - 17.04.2012 bug fixing and enhancements Development with Android and Eclipse This tutorial describes how to create Android applications with Eclipse. It is based on Eclipse 3.7 (Indigo), Java 1.6 and Android 4.0 (Ice Cream Sandwich). Table of Contents 1. What is Android? 1.1. Android Operation System 1.2. Google Play 1.3. Security and permissions 2. Android components 2.1. Activity 2.2. Views and ViewGroups 2.3. Intents 2.4. Services 2.5. ContentProvider 2.6. BroadcastReceiver 2.7. (HomeScreen) Widgets 2.8. Other 3. Android Development Tools 3.1. What are the Android Development Tools? 3.2. Dalvik Virtual Machine 3.3. How to develop Android Applications 3.4. Resource editors 4. Android Application Architecture 4.1. AndroidManifest.xml 4.2. and Resources 4.3. Assets 4.4. Activities and Layouts 4.5. Reference to resources in XML files 4.6. Activities and Lifecycle 4.7. Configuration Change 4.8. Context 5. Installation 5.1. Eclipse 5.2. Pre-requisites for using a 64bit Linux 5.3. Install ADT Plug-ins and Android SDK 5.4. Manual installation of the Android SDK 5.5. Install a specific Android version 5.6. Android Source Code 6. Android virtual device - Emulator 6.1. What is the Android Emulator? 6.2. Google vs. Android AVD 6.3. Emulator Shortcuts 6.4. Performance 6.5. Hardware button 7. Tutorial: Create and run Android Virtual Device 8. Error handling and typical problems 8.1. Workspace 8.2. Clean Project 8.3. Problems with Android Debug Bridge (adb) 8.4. LogCat 8.5. Android editor not opened converted by
  2. 2. 8.6. Emulator does not start 8.7. Timeout during deployment 8.8. Installation failed due to insufficient storage 8.9. Debug Certificate expired 8.10. Error message for @override 8.11. Missing Imports 8.12. Eclipse Tips9. Conventions for the tutorials 9.1. API version, package and application name 9.2. Warning messages for Strings10. Tutorial: Your first Android project 10.1. Install the demo application 10.2. Create Project 10.3. Modifying resources 10.4. Create attributes 10.5. Add Views 10.6. Edit View properties 10.7. Change the Activity source code 10.8. Start Project11. Starting an installed application12. OptionMenu and ActionBar 12.1. ActionBar 12.2. OptionsMenu 12.3. Creating the menu 12.4. Reacting to menu entry selection 12.5. Using the home icon 12.6. ActionBar tabs 12.7. Custom Views in the ActionBar 12.8. Contextual action mode 12.9. Context menus13. Tutorial: ActionBar 13.1. Project 13.2. Add a menu XML resource14. Tutorial: Using the contextual action mode15. Layout Manager and ViewGroups 15.1. Available Layout Manager 15.2. LinearLayout 15.3. RelativeLayout 15.4. Gridlayout 15.5. ScrollView16. Tutorial: ScrollView17. Drawables 17.1. Drawables 17.2. Shape Drawables 17.3. State Drawables 17.4. Transition Drawables 17.5. 9 Patch Drawables18. Styles and Themes 18.1. Styles 18.2. Attributes 18.3. Themes 18.4. Android Design Page19. Supporting different screen sizes 19.1. Using device independent pixel 19.2. Using resource qualifiers20. Fragments 20.1. Fragments Overview 20.2. When to use Fragments21. Fragments Tutorial 21.1. Overview 21.2. Create project 21.3. Create layouts for portrait mode 21.4. Create Fragment classes 21.5. Create layouts for landscape mode 21.6. Activities 21.7. Run22. ActionBar navigation with Fragments23. DDMS perspective and important views 23.1. DDMS - Dalvik Debug Monitor Server 23.2. LogCat View 23.3. File explorer24. Shell 24.1. Android Debugging Bridge - Shell 24.2. Uninstall an application via adb 24.3. Emulator Console via telnet25. Deployment 25.1. Overview 25.2. Deployment via Eclipse 25.3. 25.4. Via external sources 25.5. Google Play (Market) converted by
  3. 3. 26. Thank you 27. Questions and Discussion 28. Links and Literature 28.1. Source Code 28.2. Android Resources 28.3. vogella Resources1. What is Android?1.1. Android Operation SystemAndroid is an operating system based on Linux with a Java programming interface.The Android Software Development Kit (Android SDK) provides all necessary tools to develop Androidapplications. This includes a compiler, debugger and a device emulator, as well as its own virtual machineto run Android programs.Android is currently primarily developed by Google.Android allows background processing, provides a rich user interface library, supports 2-D and 3-Dgraphics using the OpenGL libraries, access to the file system and provides an embedded SQLite database.Android applications consist of different components and can re-use components of other applications, ifthese applications declare their components as available. This leads to the concept of a task in Android;an application can re-use other Android components to archive a task.For example you can write an application which integrates a map component and a camera component toarchive a certain task.1.2. Google PlayGoogle offers the "Google Play" service. Google hosts Android applications and the Google Playapplication allows to install new Android application on an Android device. Google Play used to be called"Android Market".1.3. Security and permissionsDuring deployment on an Android device, the Android system will create a unique user and group ID forevery Android application. Each application file is private to this generated user, e.g. other applicationscannot access these files.In addition each Android application will be started in its own process.Therefore by means of the underlying Linux operating system, every Android application is isolated fromother running applications. A misbehaving application cannot easily harm other Android applications.If data should be shared, the application must do this explicitly, e.g. via a Service or aContentProvider.Android also contains a permission system. Android predefines permissions for certain tasks but everyapplication can also define its own permissions.An application must declare in its configuration file (AndroidManifest.xml) that it requires certainpermissions.Depending on the details of the required permission, the Android system will either automatically grantthe permission, reject it or ask the user if he grants this permission to the application during installation.If for example the application declares that it requires Internet access, the user needs to confirm the usageof this permission during installation.This is called "user driven security". The user decides to grant a permission or to deny it. If the userdenies a permission required by the application, this application cannot be installed. The check of thepermission is only performed during installation, permissions cannot be denied or granted after theinstallation.Typically not all users check the permissions in detail but some users do. If there is something strange inthe required permissions, they will write bad reviews on Google Play.2. Android componentsThe following gives a short overview of the most important Android components.2.1. Activity converted by
  4. 4. Activity represents the presentation layer of an Android application. A simplified (and slightlyincorrect) description is that an Activity is a screen. This is slightly incorrect as Activities can bedisplayed as Dialogs or can be transparent. An Android application can have several Activities.2.2. Views and ViewGroupsViews are user interface widgets, e.g. buttons or text fields. The base class for all Views isandroid.view.View. Views often have attributes which can be used to change their appearance andbehavior.A ViewGroup is responsible for arranging other Views e.g. a ViewGroup is a layout manager. Thebase class for a layout manager is android.view.ViewGroups. ViewGroup also extends View.ViewGroups can be nestled to create complex layouts. You should not nestle ViewGroups too deeplyas this has a negative impact on the performance.2.3. IntentsIntents are asynchronous messages which allow the application to request functionality from othercomponents of the Android system, e.g. from Services or Activities. An application can call acomponent directly (explicit Intent ) or ask the Android system to evaluate registered components for acertain Intent (implicit Intents ). For example the application could implement sharing of data via anIntent and all components which allow sharing of data would be available for the user to select.Applications register themselves to an Intent via an IntentFilter.Intents allow to combine loosely coupled components to perform certain tasks.2.4. ServicesServices perform background tasks without providing a user interface. They can notify the user via thenotification framework in Android.2.5. ContentProviderContentProvider provides a structured interface to application data. Via a ContentProvider yourapplication can share data with other applications. Android contains an SQLite database which isfrequently used in conjunction with a ContentProvider to persist the data of theContentProvider.2.6. BroadcastReceiverBroadcastReceiver can be registered to receive system messages and Intents. ABroadcastReceiver will get notified by the Android system, if the specified situation happens. Forexample a BroadcastReceiver could get called once the Android system completed the boot processor if a phone call is received.2.7. (HomeScreen) WidgetsWidgets are interactive components which are primarily used on the Android homescreen. Theytypically display some kind of data and allow the user to perform actions via them. For example aWidget could display a short summary of new emails and if the user selects an email, it could start theemail application with the selected email.2.8. OtherAndroid provide many more components but the list above describes the most important ones. OtherAndroid components are "Live Folders" and "Live Wallpapers". Live Folders display data on the homescreenwithout launching the corresponding application.3. Android Development Tools3.1. What are the Android Development Tools?Google provides the Android Development Tools (ADT) to develop Android applications with Eclipse. ADTis a set of components (plug-ins) which extend the Eclipse IDE with Android development capabilities.ADT contains all required functionalities to create, compile, debug and deploy Android applications fromthe Eclipse IDE and from the command line. Other IDEs, e.g. IntellJ, are also reusing components ofADT.ADT also provides an Android device emulator, so that Android applications can be tested without a realAndroid phone. converted by
  5. 5. 3.2. Dalvik Virtual MachineThe Android system uses a special virtual machine, i.e. the Dalvik Virtual Machine to run Java basedapplications. Dalvik uses an own bytecode format which is different from Java bytecode.Therefore you cannot directly run Java class files on Android, they need to get converted in the Dalvikbytecode format.3.3. How to develop Android ApplicationsAndroid applications are primarily written in the Java programming language. The Java source files areconverted to Java class files by the Java compiler.Android provides a tool called "dx"" which converts Java class files into a dex (Dalvik Executable) file. Allclass files of one application are placed in one compressed .dex file. During this conversion processredundant information in the class files are optimized in the .dex file. For example if the same String isfound in different class files, the .dex file contains only once reference of this String.These dex files are therefore much smaller in size than the corresponding class files.The .dex file and the resources of an Android project, e.g. the images and XML files, are packed into an.apk (Android Package) file. The program aapt (Android Asset Packaging Tool) performs thispackaging.The resulting .apk file contains all necessary data to run the Android application and can be deployed toan Android device via the "adb" tool.The Android Development Tools (ADT) allows that all these steps are performed transparently to theuser; either within Eclipse or via the command line.If you use the ADT tooling you press a button or run a script and the whole Android application (.apk file)will be created and deployed.3.4. Resource editorsThe ADT allows the developer to define certain artifacts, e.g. Strings and layout files, in two ways: via arich editor, and directly via XML. This is done via multi-page editors in Eclipse. In these editors you canswitch between both representations by clicking on the tab on the lower part of the screen.For example if you open the "res/layout/main.xml" file in the Package Explorer, you can switch betweenthe two representations as depicted in the following screenshot.4. Android Application Architecture4.1. AndroidManifest.xmlThe components and settings of an Android application are described in the fileAndroidManifest.xml. For example all Activities and Services of the application must bedeclared in this file. converted by
  6. 6. It must also contain the required permissions for the application. For example if the application requiresnetwork access it must be specified here. <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="" package="" android:versionCode="1" android:versionName="1.0"> <application android:icon="@drawable/icon" android:label="@string/app_name"> <activity android:name=".Convert" android:label="@string/app_name"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> <uses-sdk android:minSdkVersion="9" /> </manifest>The package attribute defines the base package for the Java objects referred to in this file. If a Javaobject lies within a different package, it must be declared with the full qualified package name.Google Play requires that every Android application uses its own unique package. Therefore it is a goodhabit to use your reverse domain name as package name. This will avoid collisions with other and android:versionCode specify the version of your application.versionName is what the user sees and can be any String.versionCode must be an integer. The Android Market determine based on the versionCode, if itshould perform an update of the applications for the existing installations. You typically start with "1" andincrease this value by one, if you roll-out a new version of your application.The tag <activity> defines an Activity, in this example pointing to the Convert class in package. An intent filter is registered for this class whichdefines that this Activity is started once the application starts (actionandroid:name="android.intent.action.MAIN" ). The category definition categoryandroid:name="android.intent.category.LAUNCHER" defines that this application is added tothe application directory on the Android device.The @string/app_name value refers to resource files which contain the actual value of the applicationname. The usage of resource file makes it easy to provide different resources, e.g. strings, colors, icons,for different devices and makes it easy to translate applications.The "uses-sdk" part of the "AndroidManifest.xml" file defines the minimal SDK version for which yourapplication is valid. This will prevent your application being installed on devices with older SDK versions.4.2. and ResourcesThe " gen " directory in an Android project contains generated values. is a generated class whichcontains references to certain resources of the project.These resources must be defined in the "res" directory and can be XML files, icons or pictures. You can forexample define values, menus, layouts or animations via XML files.If you create a new resource, the corresponding reference is automatically created in via theEclipse ADT tools. These references are static int values and define IDs for the resources.The Android system provides methods to access the corresponding resource via these IDs.For example to access a String with the R.string.yourString ID, you would use thegetString(R.string.yourString)) is automatically created by the Eclipse development environment, manual changes are notnecessary and will be overridden by the tooling.4.3. AssetsWhile the res directory contains structured values which are known to the Android platform, the assetsdirectory can be used to store any kind of data. You access this data via the AssetsManager which youcan access the getAssets() method.AssetsManager allows to read an assets as InputStream with the open() method. // Get the AssetManager converted by
  7. 7. AssetManager manager = getAssets(); // Read a Bitmap from Assets try { InputStream open ="logo.png"); Bitmap bitmap = BitmapFactory.decodeStream(open); // Assign the bitmap to an ImageView in this layout ImageView view = (ImageView) findViewById(; view.setImageBitmap(bitmap); } catch (IOException e) { e.printStackTrace(); }4.4. Activities and LayoutsThe user interface for Activities is defined via layouts. The layout defines the included Views(widgets) and their properties.A layout can be defined via Java code or via XML. In most cases the layout is defined as an XML file.XML based layouts are defined via a resource file in the /res/layout folder. This file specifies theViewGroups, Views, their relationship and their attributes for this specific layout.If a View needs to be accessed via Java code, you have to give the View a unique ID via theandroid:id attribute. To assign a new ID to a View use @+id/yourvalue. The following shows anexample in which a Button gets the "button1" ID assigned. <Button android:id="@+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Show Preferences" > </Button>By conversion this will create and assign a new yourvalue ID to the corresponding View. In your Javacode you can later access a View via the method findViewById( layouts via XML is usually the preferred way as this separates the programming logic from thelayout definition. It also allows the definition of different layouts for different devices. You can also mixboth approaches.4.5. Reference to resources in XML filesIn your XML files, for example your layout files, you can refer to other resources via the @ sign.For example, if you want to refer to a color which is defined in a XML resource, you can refer to it via@color/your_id. Or if you defined a "hello" string in an XML resource, you could access it via@string/hello.4.6. Activities and LifecycleThe Android system controls the lifecycle of your application. At any time the Android system may stop ordestroy your application, e.g. because of an incoming call. The Android system defines a lifecycle forActivities via predefined methods. The most important methods are: onSaveInstanceState() - called if the Activity is stopped. Used to save data so that the Activity can restore its states if re-started onPause() - always called if the Activity ends, can be used to release resource or save data onResume() - called if the Activity is re-started, can be used to initialize fields4.7. Configuration ChangeAn Activity will also be restarted, if a so called "configuration change" happens. A configurationchange happens if an event is triggered which may be relevant for the application. For example if the userchanges the orientation of the device (vertically or horizontally). Android assumes that an Activitymight want to use different resources for these orientations and restarts the Activity.In the emulator you can simulate the change of the orientation via CNTR+F11.You can avoid a restart of your application for certain configuration changes via the configChangesattribute on your Activity definition in your AndroidManifest.xml. The following Activity willnot be restarted in case of orientation changes or position of the physical keyboard (hidden / visible). <activity android:name=".ProgressTestActivity" android:label="@string/app_name" converted by
  8. 8. android:configChanges="orientation|keyboardHidden|keyboard"> </activity>4.8. ContextThe class android.content.Context provides the connections to the Android system. It is theinterface to global information about the application environment. Context also provides access toAndroid Services, e.g. the Location Service. Activities and Services extend the Context classand can therefore be used as Context.5. Installation5.1. EclipseThe following assumes that you have already Java and Eclipse installed and know how to use Eclipse. Foran introduction into Eclipse please see the following tutorial: Eclipse IDE Tutorial.The tutorial above also describes how to install new components into Eclipse. This is required to installthe Android Development Tools. You find the necessary steps described in the following section of thetutorial: Eclipse Update Manager.The author of this text has also published a Kindle book on the usage of the Eclipse IDE, which can befound here: Eclipse IDE Book for Kindle.5.2. Pre-requisites for using a 64bit LinuxThe Android SDK is 32bit, therefore on a 64bit Linux system you need to have the package ia32-libsinstalled. For Ubuntu you can do this via the following command. apt-get install ia32-libsPlease check your distribution documentation, if you are using a different flavor of Linux.5.3. Install ADT Plug-ins and Android SDKUse the Eclipse update manager to install all available components for the Android Development Tools(ADT) from the URL the new Android development components are installed, you will be prompted to install the AndroidSDK. You can use the following wizard or go to the next section to learn how to do it manually. converted by
  9. 9. 5.4. Manual installation of the Android SDKAfter the installation of the ADT the Eclipse tooling allows to download the Android SDK automatically.Alternatively you can also manually download the Android SDK from the Android SDK downloadpage.The download contains a zip file, which you can extract to any place in your file system, e.g. on my Linuxsystem I placed it under "/home/vogella/android-sdks". Avoid using spaces in the path name, otherwiseyou may experience problems with the usage of the Android SDK.You also have to define the location of the Android SDK in the Eclipse Preferences. In Eclipse open thePreferences dialog via the menu Windows → Preferences. Select Android and enter the installation path ofthe Android SDK. converted by
  10. 10. 5.5. Install a specific Android versionThe Android SDK Manager allows you to install specific versions of Android. Select Window → AndroidSDK Manager from the Eclipse menu.The dialog allows you to install new packages and also allows you to delete them.Select "Available packages" and open the "Third Party Add-ons". Select the Google API 15 (Android 4.0.3)version of the SDK and press "Install". converted by
  11. 11. Press the "Install" button and confirm the license for all packages. After the installation completes, restartEclipse.5.6. Android Source CodeThe following step is optional.5.6.1. As of Android 4.0During Android development it is very useful to have the Android source code available.As of Android 4.0 the Android development tools provides also the source code. You can download it viathe Android SDK Manager by selecting the "Sources for Android SDK".The sources are downloaded to the source directory located in "path_to_android_sdk/sources/android-xx". xx is the API level of Android, e.g. 15 for the Android 4.0.3 version.To connect the sources with the android.jar file in your Android project, right click on your android.jar inthe Eclipse Package Explorer and select Properties → Java Source Attachment. Type in the source directoryname and press OK.Afterwards you can browse through the source code.5.6.2. Prior to Android 4.0For earlier versions Haris Peco maintains plugins, which provide the Android Source code code. Use theEclipse update manager to install the Android Source plugin from the following update site: "".More details can be found on the project website.6. Android virtual device - Emulator6.1. What is the Android Emulator?The Android Development Tools (ADT) includes an emulator to run an Android system. The emulatorbehaves like a real Android device (in most cases) and allows you to test your application without having areal device.You can configure the version of the Android system you would like to run, the size of the SD card, thescreen resolution and other relevant settings. You can define several of them with different configurations.These devices are called "Android Virtual Device" (AVD) and you can start several in parallel. Starting anew emulator is very slow, because the file system of the new AVD needs to get prepared.The ADT allows to deploy and run your Android program on the AVD.6.2. Google vs. Android AVDDuring the creation of an AVD you decide if you want an Android device or a Google device.An AVD created for Android will contain the programs from the Android Open Source Project. An AVDcreated for the Google APIs will also contain several Google applications, most notable the Google Mapsapplication.If you want to use functionality which is only provided via the Google APIs, e.g. Cloud2DeviceMessagingor Google Maps you must run this application on an AVD with Google APIs.6.3. Emulator ShortcutsThe following shortcuts are useful for working with the emulator.Alt+Enter Maximizes the emulator. Nice for demos.Ctrl+F11 changes the orientation of the emulator.F8 Turns network on / off.6.4. PerformanceThe graphics of the emulator are rendered in software, which is very slow. To have a responsive emulatoruse a small resolution for your emulator, as for example HVGA.Also if you have sufficient memory on your computer, add at least 1 GB of memory to your emulator. Thisis the value "Device ram size" during the creation of the AVD. converted by
  12. 12. Also set the flag "Enabled" for Snapshots. This will save the state of the emulator and will let it start muchfaster.6.5. Hardware buttonAndroid 4.0 introduced that devices do not have to have hardware button anymore. If you want to createsuch an AVD, add the "Hardware Back/Home keys" property to the device configuration and set it to"false".7. Tutorial: Create and run Android VirtualDeviceTo define an Android Virtual Device (ADV) open the "AVD Manager" via Windows → AVD Manager andpress "New".Enter the following. converted by
  13. 13. We can also select the box "Enabled" for Snapshots. This will make the second start of the virtual devicemuch faster.At the end press the button "Create AVD". This will create the AVD configuration and display it under the"Virtual devices".To test if your setup is correct, select your device and press "Start".After (a long time) your AVD starts. You are able to use it via the mouse and via the virtual keyboard ofthe emulator.8. Error handling and typical problemsThings are not always working as they should. This section gives an overview over typical problems andhow to solve them.8.1. WorkspaceNever use a workspace in Eclipse which has spaces in the directory path name, this may lead to severalstrange problems.8.2. Clean ProjectSeveral users report that they get the following errors: 1. Project ... is missing required source folder: gen 2. The project could not be built until build path errors are resolved. 3. Unable to open class file solve any of these errors, go to the project menu and select Project → Clean.8.3. Problems with Android Debug Bridge (adb)The communication with the emulator or your Android device might have problems. This communicationis handled by the Android Debug Bridge (adb).Eclipse allows to reset the adb in case this causes problems. Select therefore the DDMS perspective viaWindow → Open Perspective → Other → DDMSTo restart the adb, select the "Reset adb" in the Device View. converted by
  14. 14. 8.4. LogCatThe "LogCat" View shows you the log messages of your Android device and helps you to analyzeproblems. For example Java exceptions in your program would be shown here. To open this view, selectWindow → Show View → Other → Android → LogCat.8.5. Android editor not openedAndroid provides nice editors to edit Android resource files, unfortunately these editor are not alwaysautomatically used due to bugs in the ADT. If that happens, you can open this editor manually. Right-clickon your menu file and select Open with → Android Menu Editor.8.6. Emulator does not startIf your emulator does not start, make sure that the android-sdk version is in a path without any spaces inthe path name.8.7. Timeout during deploymentIf you face timeout issues during deployment you can increase the default timeout in the Eclipsepreferences. Select Window → Preferences → Android → DDMS and increase the "ADB connectiontimeout (in ms)" value.8.8. Installation failed due to insufficient storageSometimes the emulator will refuse to install an application with the error message:INSTALL_FAILED_INSUFFICIENT_STORAGE.An Android virtual device provides per default only 64M for the storaging Android applications. You canclean your installed application by re-starting the emulator and selecting the "Wipe user data" flag.Alternatively you can set the data partition size. If you press edit on the AVD, you can set the "Ideal sizeof data partition" property via the "New" button. converted by
  15. 15. 8.9. Debug Certificate expiredIf you get the error message "Debug Certificate expired" switch to the folder which contains the AndroidAVD, e.g. ".android" under Linux and delete the "debug.keystore" file. This file is only valid for a year andif not present, Eclipse will regenerate the password.8.10. Error message for @overrideThe @override annotation was introduced in Java 1.6. If you receive an error message for @override,change the Java compiler level to Java 1.6. To do this, right-click on the project, select Properties → JavaCompiler → Compiler compliance level and select "1.6" in the drop-down box.8.11. Missing ImportsJava requires that classes which are not part of the standard Java Language are either fully qualified ordeclared via imports.If you see an error message with "XX cannot be resolved to a variable", right-click in your Editor andselect Source → Organize Imports to important required packages.8.12. Eclipse TipsTo work more efficiently with Eclipse, select Window → Preferences → Java → Editor → Save Actions andselect that the source code should be formated and that the imports should be organized at every saveaction.9. Conventions for the tutorials9.1. API version, package and application nameThe tutorials of this document have been developed and tested with Android 4.0.4, API Level 15. Pleaseuse this version for all tutorials in this book. Higher versions of the API level should also work. A lowerversion of the Android API might also work, but if you face issues, try the recommended version.The base package for the projects is always the same as the project name, e.g. if you are asked to createa project "" then the corresponding package name is"".The application name, which must be entered on the Android project generation wizard, will not bepredefined. Choose a name you like.9.2. Warning messages for StringsThe Android development tools show warnings, if you use hard-coded strings, for example in layout files.For real applications you should use String resource files. To simplify the creation of the examples, we useStrings directly. Please ignore the corresponding warnings.10. Tutorial: Your first Android project10.1. Install the demo applicationThis application is also available on the Android Marketplace under Android Temperature converter .Alternatively you can also scan the following barcode with your Android smartphone to install it via theGoogle Play application.10.2. Create ProjectSelect File → New → Other → Android → Android Project and create the Android project"". Enter the following. converted by
  16. 16. Press "Finish". This should create the following directory structure. converted by
  17. 17. 10.3. Modifying resourcesAs described in the Android Development Tools (ADT) chapter, ADT provides specialized editors forresources files, e.g. layout files. These editors allow to switch between the XML representation of the fileand a richer user interface via tabs on the bottom of the editor.The following description uses the rich user interface to build layout files. For validation purposes, theresulting XML is also included in the description.10.4. Create attributesAndroid allows you to create static attributes, e.g. Strings or colors. These attributes can for example beused in your XML layout files or referred to via Java source code.Select the file "res/values/string.xml" and press the "Add" button. Select "Color" and enter "myColor" asthe name and "#3399CC" as the value.Add the following "String" attributes. String attributes allow the developer to translate the application at alater point.Table 1. String Attributes Name Value celsius to Celsius fahrenheit to Fahrenheit calc CalculateSwitch to the XML representation and validate that the values are correct. <?xml version="1.0" encoding="utf-8"?> <resources> converted by
  18. 18. <string name="hello">Hello World, Convert!</string> <string name="app_name">Temperature Converter</string> <color name="myColor">#3399CC</color> <string name="myClickHandler">myClickHandler</string> <string name="celsius">to Celsius</string> <string name="fahrenheit">to Fahrenheit</string> <string name="calc">Calculate</string> </resources>10.5. Add ViewsSelect "res/layout/main.xml" and open the Android editor via a double-click. This editor allows you tocreate the layout via drag and drop or via the XML source code. You can switch between bothrepresentations via the tabs at the bottom of the editor. For changing the position and grouping elementsyou can use the Eclipse "Outline" view.The following shows a screenshot of the "Palette" view from which you can drag and drop new userinterface components into your layout. Please note that the "Palette" view changes frequently so your viewmight be a bit different.You will now create your new layout.Right-click on the existing text object “Hello World, Hello!” in the layout. Select "Delete" from the popupmenu to remove the text object. Then, from the “Palette” view, select Text Fields and locate "Plain Text".Drag this onto the layout to create a text input field. All object types in the section "Text Fields” derivefrom the class "EditText", they just specify via an additional attribute which text type can be used.Afterwards select the Palette section "Form Widgets" and drag a “RadioGroup” object onto the layout. Thenumber of radio buttons added to the radio button group depends on your version of Eclipse. Make surethere are two radio buttons by deleting or adding radio buttons to the group.From the Palette section Form Widgets, drag a Button object onto the layout.The result should look like the following.Switch to "main.xml" and verify that your XML looks like the following. <?xml version="1.0" encoding="utf-8"?> converted by
  19. 19. <LinearLayout xmlns:android="" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <EditText android:id="@+id/editText1" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="EditText" > </EditText> <RadioGroup android:id="@+id/radioGroup1" android:layout_width="match_parent" android:layout_height="wrap_content" > <RadioButton android:id="@+id/radio0" android:layout_width="wrap_content" android:layout_height="wrap_content" android:checked="true" android:text="RadioButton" > </RadioButton> <RadioButton android:id="@+id/radio1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="RadioButton" > </RadioButton> </RadioGroup> <Button android:id="@+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Button" > </Button> </LinearLayout>10.6. Edit View propertiesIf you select a user interface component (an instance of View ), you can change its properties via theEclipse "Properties" view. Most of the properties can be changed via the right mouse menu. You can alsoedit properties of fields directly in XML. Changing properties in the XML file is much faster, if you knowwhat you want to change. But the right mouse functionality is nice, if you are searching for a certainproperty.Open your file "main.xml". The EditText control shows currently a default text. We want to delete thisinitial text in the XML code. Switch to the XML tab called "main.xml" and delete theandroid:text="EditText" property from the EditText part. Switch back to the "Graphical Layout"tab and check that the text is removed.Use the right mouse click on the first radio button to assign the "celsius" String attribute to its "text"property. Assign the "fahrenheit" string attribute to the second radio button. converted by
  20. 20. From now on, I assume you are able to use the properties menu on user interface components. You canalways either edit the XML file or modify the properties via right mouse click.Set the property "Checked" to true for the first RadioButton.Assign "calc" to the text property of your button and assign "myClickHandler" to the "onClick" property.Set the "Input type" property to "numberSigned" and "numberDecimal" on your EditText.All your user interface components are contained in a LinearLayout. We want to assign a backgroundcolor to this LinearLayout. Right-click on an empty space in Graphical Layout mode, then select OtherProperties → All by Name → Background. Select “Color” and then select "myColor" "in the list which isdisplayed.Switch to the "main.xml" tab and verify that the XML is correct. <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="" android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="@color/myColor" android:orientation="vertical" > <EditText android:id="@+id/editText1" android:layout_width="match_parent" android:layout_height="wrap_content" android:inputType="numberDecimal|numberSigned" > </EditText> <RadioGroup android:id="@+id/radioGroup1" android:layout_width="match_parent" android:layout_height="wrap_content" > <RadioButton android:id="@+id/radio0" android:layout_width="wrap_content" android:layout_height="wrap_content" android:checked="true" android:text="@string/celsius" > </RadioButton> <RadioButton android:id="@+id/radio1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/fahrenheit" > </RadioButton> converted by
  21. 21. </RadioGroup> <Button android:id="@+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:onClick="myClickHandler" android:text="@string/calc" > </Button> </LinearLayout>10.7. Change the Activity source codeDuring the generation of your new Android project you specified that an Activity calledConvertActivity should be created. The project wizard created the corresponding Java class.Change your code in to the following. Note that the myClickHandler willbe called based on the OnClick property of your button. package; import; import android.os.Bundle; import android.view.View; import android.widget.EditText; import android.widget.RadioButton; import android.widget.Toast; public class ConvertActivity extends Activity { private EditText text; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); text = (EditText) findViewById(; } // This method is called at button click because we assigned the name to the // "On Click property" of the button public void myClickHandler(View view) { switch (view.getId()) { case RadioButton celsiusButton = (RadioButton) findViewById(; RadioButton fahrenheitButton = (RadioButton) findViewById(; if (text.getText().length() == 0) { Toast.makeText(this, "Please enter a valid number", Toast.LENGTH_LONG).show(); return; } float inputValue = Float.parseFloat(text.getText().toString()); if (celsiusButton.isChecked()) { text.setText(String .valueOf(convertFahrenheitToCelsius(inputValue))); celsiusButton.setChecked(false); fahrenheitButton.setChecked(true); } else { text.setText(String .valueOf(convertCelsiusToFahrenheit(inputValue))); fahrenheitButton.setChecked(false); celsiusButton.setChecked(true); } break; } } // Converts to celsius private float convertFahrenheitToCelsius(float fahrenheit) { return ((fahrenheit - 32) * 5 / 9); } // Converts to fahrenheit private float convertCelsiusToFahrenheit(float celsius) { return ((celsius * 9) / 5) + 32; } }10.8. Start ProjectTo start the Android Application, select your project, right click on it, and select Run-As → AndroidApplication. If an emulator is not yet running, it will be started. Be patient, the emulator starts up veryslowly.You should get the following result. converted by
  22. 22. Type in a number, select your conversion and press the button. The result should be displayed and theother option should get selected.11. Starting an installed applicationAfter you run your application on the virtual device, you can start it again on the device. If you press the"Home" button you can select your application. converted by
  23. 23. 12. OptionMenu and ActionBar12.1. ActionBarThe ActionBar is located at the top of the Activity that may display the Activity title, navigationmodes, and other interactive items.The following picture show the ActionBar of a typical Google Application with interactive items and anagivation bar.12.2. OptionsMenuThe application can also open a menu which shows actions via a popup menu. This OptionsMenu isonly available if the phone has a hardware "Options" button. Even if the hardware button is available, it isrecommended to use the ActionBar, which is available for phones as of Android 4.0.The following picture highlights the hardware button and the resulting menu as popup. converted by
  24. 24. One of the reasons why the ActionBar is superior to the OptionsMenu, if that it is clearly visible,while the OptionsMenu is only shown on request and the user may not recognize that options areavailable.12.3. Creating the menuThe OptionsMenu and the ActionBar is filled by the onCreateOptionsMenu() method of yourActivity.In the onCreateOptionsMenu() method you can create the menu entries. You can add menu entriesvia code or via the inflation of an existing XML resources.The MenuInflator class allows to inflate menu entries defined in XML to the menu. MenuInflatorcan get accessed via the getMenuInflator() method in your Activity.The onCreateOptionsMenu() method is only called once. If you want to influence the menu later youhave to use the onPrepareOptionsMenu() method. onPrepareOptionsMenu() is not called forentries in the ActionBar for these entries you have to use the invalidateOptionsMenu() method.12.4. Reacting to menu entry selectionIf a menu entry is selected then then onOptionsItemSelected() method is called. As parameter youreceive the menu entry which was selected so that you can react differently to different menu entries.12.5. Using the home iconThe ActionBar also shows an icon of your application. You can also add an action to this icon. If youselect this icon the onOptionsItemSelected() method will be called with the The recommendation is to return to the main Activity in your program. // If home icon is clicked return to main Activity case Intent intent = new Intent(this, OverviewActivity.class); intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP); startActivity(intent); break;12.6. ActionBar tabsIt is also possible to add tabs to the ActionBar which can be used for navigation. Typically Fragmentsare used for this purpose. We demonstrate this in the Fragments chapter.12.7. Custom Views in the ActionBarYou can also add a custom View to the ActionBar. The following code snippet demonstrates that. @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); ActionBar actionBar = getActionBar(); // add the custom view to the action bar converted by
  25. 25. // add the custom view to the action bar actionBar.setCustomView(R.layout.actionbar_view); actionBar.setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM | ActionBar.DISPLAY_SHOW_HOME); }12.8. Contextual action modeA contextual action mode activates a temporary ActionBar that overlays the application ActionBar forthe duration of a particular sub-task.The contextual action mode is typically activated by selecting an item or by long clicking on it.To implemented this, call the startActionMode() method on a View or on your Activity. Thismethod gets an ActionMode.Callback object which is responsible for the lifecycle of the contextualActionBar.12.9. Context menusYou can also assign a context menu to a View. A context menu is also activated if the user "long presses"the view.If possible the contextual action mode should be preferred over a context menu.A context menu for a view is registered via the registerForContextMenu(view) method. TheonCreateContextMenu() method is called every time a context menu is activated as the contextmenu is discarded after its usage. The Android platform may also add options to your View, e.g.EditText provides context options to select text, etc.13. Tutorial: ActionBar13.1. ProjectThis chapter will demonstrate how to create items in the ActionBar and react to the selection of theuser.Create a project called "" with the Activity called "OverviewActivity".13.2. Add a menu XML resourceSelect your project, right click on it and select New → Other → Android → Android XML File to create anew XML resource.Select the option "Menu", enter as File "mainmenu.xml" and press the button "Finish".This will create a new file "mainmenu.xml" in the folder "res/menu" of your project. Open this file andselect the "Layout" tab of the Android editor.Press Add and select "Item". Maintain a entry similar to the following screenshot. Via the "ifRoom"attribute you define that the menu entry is displayed in the ActionBar if there is sufficient spaceavailable. converted by
  26. 26. Add a similar entry to the menu with the ID set to "@+id/menuitem2", the Title set to "Test". Also set the"ifRoom" flag.The resulting XML will look like the following. <?xml version="1.0" encoding="utf-8"?> <menu xmlns:android="" > <item android:id="@+id/menuitem1" android:showAsAction="ifRoom" android:title="Prefs"> </item> <item android:id="@+id/menuitem2" android:showAsAction="ifRoom" android:title="Test"> </item> </menu>Change your Activity class "OverviewActivity" to the following. package; import; import android.os.Bundle; import android.view.Menu; import android.view.MenuInflater; import android.view.MenuItem; import android.widget.Toast; public class OverviewActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { switch (item.getItemId()) { case Toast.makeText(this, "Menu Item 1 selected", Toast.LENGTH_SHORT) .show(); break; case Toast.makeText(this, "Menu item 2 selected", Toast.LENGTH_SHORT) .show(); break; default: break; } converted by
  27. 27. return true; } }Run your application. As there is enough space in the ActionBar otherwise you may see the Overflowmenu or you have to use the "Option" menu button on your phone. If you select one item, you should seea small info message.14. Tutorial: Using the contextual action modeAdd a EditText element your your "main.xml" layout file. <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" > <EditText android:id="@+id/myView" android:layout_width="match_parent" android:layout_height="wrap_content" android:ems="10" > <requestFocus /> </EditText> </LinearLayout>Create a new menu XML resource with the file name "contextual.xml" <?xml version="1.0" encoding="utf-8"?> <menu xmlns:android="" > <item android:id="@+id/toast" android:title="Toast"> </item> </menu>Change your Activity to the following. package; import; import android.os.Bundle; import android.view.Menu; import android.view.MenuInflater; import android.view.MenuItem; import android.widget.Toast; public class OverviewActivity extends Activity { protected Object mActionMode; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // Define the contextual action mode converted by
  28. 28. View view = findViewById(; view.setOnLongClickListener(new View.OnLongClickListener() { // Called when the user long-clicks on someView public boolean onLongClick(View view) { if (mActionMode != null) { return false; } // Start the CAB using the ActionMode.Callback defined above mActionMode = OverviewActivity.this .startActionMode(mActionModeCallback); view.setSelected(true); return true; } }); } @Override public boolean onCreateOptionsMenu(Menu menu) { MenuInflater inflater = getMenuInflater(); inflater.inflate(, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { Toast.makeText(this, "Just a test", Toast.LENGTH_SHORT).show(); return true; } private ActionMode.Callback mActionModeCallback = new ActionMode.Callback() { // Called when the action mode is created; startActionMode() was called public boolean onCreateActionMode(ActionMode mode, Menu menu) { // Inflate a menu resource providing context menu items MenuInflater inflater = mode.getMenuInflater(); // Assumes that you have "contexual.xml" menu resources inflater.inflate(, menu); return true; } // Called each time the action mode is shown. Always called after // onCreateActionMode, but // may be called multiple times if the mode is invalidated. public boolean onPrepareActionMode(ActionMode mode, Menu menu) { return false; // Return false if nothing is done } // Called when the user selects a contextual menu item public boolean onActionItemClicked(ActionMode mode, MenuItem item) { switch (item.getItemId()) { case Toast.makeText(OverviewActivity.this, "Selected menu", Toast.LENGTH_LONG).show(); mode.finish(); // Action picked, so close the CAB return true; default: return false; } } // Called when the user exits the action mode public void onDestroyActionMode(ActionMode mode) { mActionMode = null; } }; }If you run this example and long press the EditText widget, your contextual ActionBar is displayed.15. Layout Manager and ViewGroups15.1. Available Layout ManagerA layout manager is a subclass of ViewGroup and is responsible for the layout of itself and its childViews. Android supports different default layout managers.As of Android 4.0 the most relevant layout manager are LinearLayout, FrameLayout,RelativeLayout and GridLayout.All layouts allow the developer to define attributes. Children can also define attributes which may beevaluated by their parent layout. converted by
  29. 29. AbsoluteLayoutLayout is deprecated and TableLayout can be implemented more effectively viaGridLayout15.2. LinearLayoutLinearLayout puts all its child elements into a single column or row depending on theandroid:orientation attribute. Possible values for this attribute are horizontal and vertical,horizontal is the default value.LinearLayout can be nested to achieve more complex layouts.15.3. RelativeLayoutRelativeLayout allow to position the widget relative to each other. This allows for complex layouts.A simple usage for RelativeLayout is if you want to center a single component. Just add onecomponent to the RelativeLayout and set the android:layout_centerInParent attribute totrue. <?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" > <ProgressBar android:id="@+id/progressBar1" style="?android:attr/progressBarStyleLarge" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerInParent="true" /> </RelativeLayout>15.4. GridlayoutGridLayout was introduced with Android 4.0. This layout allows you to organize a view into a Grid.GridLayout separates its drawing area into: rows, columns, and cells.You can specify how many columns you want for define for each View in which row and column it shouldbe placed and how many columns and rows it should use. If not specified GridLayout uses defaults,e.g. one column, one row and the position of a View depends on the order of the declaration of theViews.15.5. ScrollViewScrollViews can be used to contain one view that might be to big to fit on one screen. If the view is to bigthe ScrollView will display a scroll bar to scroll the context. Of course this view can be a layout which canthen contain other elements.16. Tutorial: ScrollViewCreate an android project "" with the activity "ScrollView". Create thefollowing layout and class. <?xml version="1.0" encoding="utf-8"?> <ScrollView xmlns:android="" android:layout_width="fill_parent" android:layout_height="fill_parent" android:fillViewport="true" android:orientation="vertical" > <LinearLayout android:id="@+id/LinearLayout01" android:layout_width="fill_parent" android:layout_height="wrap_content" android:orientation="vertical" > <TextView android:id="@+id/TextView01" android:layout_width="wrap_content" android:layout_height="wrap_content" android:paddingLeft="8dip" android:paddingRight="8dip" android:paddingTop="8dip" android:text="This is a header" android:textAppearance="?android:attr/textAppearanceLarge" > </TextView> <TextView android:id="@+id/TextView02" android:layout_width="wrap_content" converted by
  30. 30. android:layout_height="fill_parent" android:layout_weight="1.0" android:text="@+id/TextView02" > </TextView> <LinearLayout android:id="@+id/LinearLayout02" android:layout_width="wrap_content" android:layout_height="wrap_content" > <Button android:id="@+id/Button01" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_weight="1.0" android:text="Submit" > </Button> <Button android:id="@+id/Button02" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_weight="1.0" android:text="Cancel" > </Button> </LinearLayout> </LinearLayout> </ScrollView> package; import; import android.os.Bundle; import android.view.View; import android.widget.TextView; public class ScrollView extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); TextView view = (TextView) findViewById(; String s=""; for (int i=0; i < 100; i++) { s += " "; } view.setText(s); } }The attribute "android:fillViewport="true"" ensures that the scrollview is set to the full screen even if theelements are smaller then one screen and the "layout_weight" tell the android system that these elementsshould be extended.17. Drawables17.1. DrawablesA instance of a Drawable resource is a general concept for a graphic which can be drawn. The simplestcase is a bitmap file, which would be represented in Android via a BitmapDrawable class. Bitmaps are converted by
  31. 31. typically stored in one of the "res/drawable" folders. The Android project creation wizard creates severalof these folders per default, you can provide different sized files for different resolutions of Androiddevices. If you only provideIn additional to graphical files, Android supports XML drawables and 9-patch graphics. XML drawables areused to describe shapes (color, border, gradient), State and Transitions and more.9-patch graphics are used to define which part of a graphic should be increased if the View which usesthis graphic is larger then the graphic.17.2. Shape DrawablesShape Drawables are XML files which allow to define a geometric object with colors, borders andgradients which can get assigned to Views. The advantage of using XML Shape Drawables is that theyautomatically adjust to the correct size.The following listing shows an example of a Shape Drawable. <?xml version="1.0" encoding="UTF-8"?> <shape xmlns:android="" android:shape="rectangle"> <stroke android:width="2dp" android:color="#FFFFFFFF" /> <gradient android:endColor="#DDBBBBBB" android:startColor="#DD777777" android:angle="90" /> <corners android:bottomRightRadius="7dp" android:bottomLeftRadius="7dp" android:topLeftRadius="7dp" android:topRightRadius="7dp" /> </shape>You could for example assign that drawable to the background property of your layout. <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="" android:layout_width="fill_parent" android:layout_height="fill_parent" android:background="@drawable/myshape" android:orientation="vertical" > <EditText android:id="@+id/editText1" android:layout_width="match_parent" android:layout_height="wrap_content" > </EditText> <RadioGroup android:id="@+id/radioGroup1" android:layout_width="match_parent" android:layout_height="wrap_content" > <RadioButton android:id="@+id/radio0" android:layout_width="wrap_content" android:layout_height="wrap_content" android:checked="true" android:text="@string/celsius" > </RadioButton> <RadioButton android:id="@+id/radio1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/fahrenheit" > </RadioButton> </RadioGroup> <Button android:id="@+id/button1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/calc" android:onClick="myClickHandler"> </Button> </LinearLayout>17.3. State DrawablesState drawables allow to define states. For each state a different drawable can get assigned to the View.For example the following defines different drawables for a button depending on its state. <?xml version="1.0" encoding="utf-8"?> <selector xmlns:android=""> converted by
  32. 32. <item android:drawable="@drawable/button_pressed" android:state_pressed="true" /> <item android:drawable="@drawable/button_checked" android:state_checked="true" /> <item android:drawable="@drawable/button_default" /> </selector>17.4. Transition DrawablesTransition Drawables allow to define transitions which can be triggered in the coding. <?xml version="1.0" encoding="utf-8"?> <transition xmlns:android=""> <item android:drawable="@drawable/first_image" /> <item android:drawable="@drawable/second_image" /> </transition> final ImageView image = (ImageView) findViewById(; final ToggleButton button = (ToggleButton) findViewById(; button.setOnClickListener(new OnClickListener() { @Override public void onClick(final View v) { TransitionDrawable drawable = (TransitionDrawable) image.getDrawable(); if (button.isChecked()) { drawable.startTransition(500); } else { drawable.reverseTransition(500); } } });17.5. 9 Patch Drawables9 Patch drawables are drawables which have a one pixel additional border. On the top and left you definethe area which should grow if the drawable is to small for the View.On the right and bottom side you define where a text should be placed if this Drawable is used on aView which can write text on it, e.g. a Button.The ADT supplies the "draw9patch" program in the "android-sdk/tools" installation folder, which makes iteasy to create 9 patch drawables.18. Styles and Themes18.1. StylesStyles in Android allow to define the look and feel of Android application in external files. Styles can getassigned to Views.You can define styles in XML and assign them to these elements. This way you only have to set commonattributes once and can later change the look in one central place.To define a style, save an XML file in the /res/values" directory of your project. The root node of the XMLfile must be <resources> .The following "styles.xml" XML file would be created in the "/res/xml" folder. <?xml version="1.0" encoding="utf-8"?> <resources> <style name="text"> <item name="android:padding">4dip</item> <item name="android:textAppearance">?android:attr/textAppearanceLarge</item> <item name="android:textColor">#000000</item> </style> <style name="layout"> <item name="android:background">#C0C0C0</item> </style> </resources>You assign the style attribute to your elements, for example to the text elements via style=”@style/text”.18.2. AttributesYou can also refer to individual attributes of Android styles. For example the following will define buttonwith the Android 4.0 button style. <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="" android:layout_width="fill_parent" converted by
  33. 33. android:layout_height="fill_parent" android:orientation="vertical" > <LinearLayout style="?android:attr/buttonBarStyle" android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="horizontal" > <Button android:id="@+id/Button01" style="?android:attr/buttonBarButtonStyle" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:text="Show" /> <Button android:id="@+id/Button02" style="?android:attr/buttonBarButtonStyle" android:layout_width="0dp" android:layout_height="wrap_content" android:layout_weight="1" android:text="Change" /> </LinearLayout> <EditText android:id="@+id/myView" android:layout_width="match_parent" android:layout_height="wrap_content" android:ems="10" > <requestFocus /> </EditText> </LinearLayout>18.3. ThemesA theme is a style applied to an entire Activity or application, rather than an individual View (as in theexample above).The next example show how to define your own Theme while extending a platform theme. <?xml version="1.0" encoding="utf-8"?> <resources> <style name="MyTheme" parent="android:Theme.Light"> <item name="android:windowNoTitle">true</item> <item name="android:windowBackground">@color/translucent_red</item> <item name="android:listViewStyle">@style/MyListView</item> </style> <style name="MyListView" parent="@android:style/Widget.ListView"> <item name="android:listSelector">@drawable/ic_menu_home</item> </style> </resources>18.4. Android Design PageHow to design your Android application is described on the Android Design Pages, which can be foundhere . converted by
  34. 34. This page also contains several downloadable resources, e.g. an Icon set for the ActionBar.19. Supporting different screen sizes19.1. Using device independent pixelAndroid devices are different in terms of resolution and in terms of density. Therefore it is recommendednever to use fixed sized dimensions.The unit of measurement which should be used is "dp" (which is the same as "dip" but shorter). dp refersto the base line of an Android device, e.g. 320x480 with 160dpi (dots per inch), which was the size of thefirst Android device (G1). This size is also known as mdpi (medium dots per inch).If you specify the size in "dp", Android will automatically scale it, depending on the device. On a mdpidevice "dp" will be equal to pixel but it will be smaller on a ldpi (approx. 120dip) and larger on a hdip(approx. 240dpi) device, so that it always occupies the same physical space.You can use "dp" in your resources, e.g. layout files. The Android SDK expects that you specify everythingin pixels. You can therefore use the following formulator to calculate the right amount of pixels for adimension specified in dp. public int convertToDp(int input) { // Get the screens density scale final float scale = getResources().getDisplayMetrics().density; // Convert the dps to pixels, based on density scale return (int) (input * scale + 0.5f); }19.2. Using resource qualifiersAndroid also allows to use resource qualifiers to specify that certain resources should only be used forcertain resolutions or configurations. For example your can provide a special "main.xml" layout file for adevice in landscape mode, if you place such a file in the "res/layout-land" folder.The different resource qualifiers are described on the following webpage: Providing Resources20. Fragments20.1. Fragments OverviewFragment components allow you to organize your application code so that it is easier to support differentsized devices.Fragments are components with their own lifecycle and their own user interface. They can be definedvia layout files or via coding.Fragments always run in the context of an Activity. If an Activity is stopped its Fragments willalso be stopped; if an Activity is destroyed its Fragments will also get destroyed.If a Fragment component is defined in an XML layout file, the android:name attribute points to theFragments class.The base class for Fragments is For special purposes you can also usemore special classes, like ListFragment or DialogFragment.The onCreateView() method is called by Android once the Fragment should create its user interface.Here you can inflate an layout. The onStart() method is called once the Fragment getsvisible.Fragments can be dynamically added and removed from an Activity via Fragment transactions.This will add the action to the history stack of the Activity, i.e. this will allow to revert the Fragmentchanges in the Activity via the back button.20.2. When to use FragmentsFragments make it easy to re-use components in different layouts, e.g. you can build single-panelayouts for handsets (phones) and multi-pane layouts for tablets.This is not limited to tablets; for example you can use Fragments also to support different layout forlandscape and portrait orientation. But as tablets offer significantly more space you typically include moreviews into the layout and Fragments makes that easier.The typical example is a list of items in an activity. On a tablet you see the details immediately on the converted by
  35. 35. same screen on the right hand side if you click on item. On a handset you jump to a new detail screen.The following discussion will assume that you have two Fragments (main and detail) but you can alsohave more. We will also have one main activity and one detailed activity. On a tablet the main activitycontains both Fragments in its layout, on a handheld it only contains the main fragment.To check for an fragment you can use the FragmentManager. DetailFragment fragment = (DetailFragment) getFragmentManager(). findFragmentById(; if (fragment==null || ! fragment.isInLayout()) { // start new Activity } else { fragment.update(...); }To create different layouts with Fragments you can: Use one activity, which displays two Fragments for tablets and only one on handsets devices. In this case you would switch the Fragments in the activity whenever necessary. This requires that the fragment is not declared in the layout file as such Fragments cannot be removed during runtime. It also requires an update of the action bar if the action bar status depends on the fragment. Use separate activities to host each fragment on a handset. For example, when the tablet UI uses two Fragments in an activity, use the same activity for handsets, but supply an alternative layout that includes just one fragment. When you need to switch Fragments, start another activity that hosts the other fragment.The second approach is the most flexible and in general preferable way of using Fragments. In this casethe main activity checks if the detail fragment is available in the layout. If the detailed fragment is there,the main activity tells the fragment that is should update itself. If the detail fragment is not available themain activity starts the detailed activity.It is good practice that Fragments do not manipulate each other. For this purpose a Fragment typicallyimplements an interface to get new data from its host Activity.21. Fragments Tutorial21.1. OverviewThe following tutorial demonstrates how to use Fragments. The entry Activity (calledMainActivity of our application ) will use different layouts for portrait and for landscape mode.In portrait mode MainActivity will show one Fragment with a list of names. If the user touches anitem in the list, a second Activity called DetailActivity will start and show the selected text.In landscape mode MainActivity will show two Fragments. The first is again the Fragments whichshows the list of names. The second Fragment shows the text of the current selected item. This issimilar to the portrait mode, but the whole information will be shown on one screen.21.2. Create projectCreate a new project with an Activity called MainActivity.21.3. Create layouts for portrait modeCreate or change the following layout files in the "res/layout/" folder.First create the following file called "details.xml". This layout will be used by the DetailFragment. <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" > <TextView android:id="@+id/detailsText" android:layout_width="wrap_content" android:layout_height="match_parent" android:layout_gravity="center_horizontal|center_vertical" android:layout_marginTop="20dip" android:text="Large Text" android:textAppearance="?android:attr/textAppearanceLarge" android:textSize="30dip" /> </LinearLayout> converted by
  36. 36. Change the existing "main.xml" file. This layout will be used by MainActivity in landscape mode andshows two Fragments. <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="horizontal" > <fragment android:id="@+id/listFragment" android:layout_width="150dip" android:layout_height="match_parent" android:layout_marginTop="?android:attr/actionBarSize" class="" ></fragment> <fragment android:id="@+id/detailFragment" android:layout_width="match_parent" android:layout_height="match_parent" class="" > <!-- Preview: layout=@layout/details --> </fragment> </LinearLayout>21.4. Create Fragment classesCreate now the Fragment classes. Create the ListFragment class. package; import android.content.Intent; import android.os.Bundle; import android.view.View; import android.widget.ArrayAdapter; import android.widget.ListView; public class ListFragment extends { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); } @Override public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); String[] values = new String[] { "Android", "iPhone", "WindowsMobile", "Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X", "Linux", "OS/2" }; ArrayAdapter<String> adapter = new ArrayAdapter<String>(getActivity(), android.R.layout.simple_list_item_1, values); setListAdapter(adapter); } @Override public void onListItemClick(ListView l, View v, int position, long id) { String item = (String) getListAdapter().getItem(position); DetailFragment fragment = (DetailFragment) getFragmentManager() .findFragmentById(; if (fragment != null && fragment.isInLayout()) { fragment.setText(item); } else { Intent intent = new Intent(getActivity().getApplicationContext(), DetailActivity.class); intent.putExtra("value", item); startActivity(intent); } } }Create the DetailFragment class. package; import; import android.os.Bundle; import android.util.Log; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.TextView; public class DetailFragment extends Fragment { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Log.e("Test", "hello"); } @Override converted by
  37. 37. public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); } @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { View view = inflater.inflate(R.layout.details, container, false); return view; } public void setText(String item) { TextView view = (TextView) getView().findViewById(; view.setText(item); } }21.5. Create layouts for landscape modeWe want that Android uses a different main.xml file in portrait model then in landscape mode.For this reason create the "res/layout-port" folder.In portrait mode Android will check the "layout-port" folder for fitting layout files. Only if we would nothave a "main.xml" file in "layout-port", Android would check the "layout" folder.Therefore create the following "main.xml" layout file in "res/layout-port". <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="horizontal" > <fragment android:id="@+id/listFragment" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginTop="?android:attr/actionBarSize" class="" /> </LinearLayout>Also create the "details_activity_layout.xml" layout file. This layout will be used in the DetailActivitywhich is only used in portrait mode. Please note that we could have create this file also in the "layout"folder, but as it is only used in portrait mode it is best practise to place it into this folder. <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" > <fragment android:id="@+id/detailFragment" android:layout_width="match_parent" android:layout_height="match_parent" class="" /> </LinearLayout>21.6. ActivitiesCreate a new Activity called DetailActivity with the following class. package; import; import android.content.res.Configuration; import android.os.Bundle; import android.widget.TextView; public class DetailActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); // Need to check if Activity has been switched to landscape mode // If yes, finished and go back to the start Activity if (getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE) { finish(); return; } setContentView(R.layout.details_activity_layout); Bundle extras = getIntent().getExtras(); if (extras != null) { String s = extras.getString("value"); TextView view = (TextView) findViewById(; view.setText(s); converted by
  38. 38. } } }MainActivity will remain unmodified. package; import; import android.os.Bundle; public class MainActivity extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); } }21.7. RunRun your example. If you run the application in portrait mode you should see only one Fragment. UseCtrl+F11 to switch the orientation. In horizontal mode you should see two Fragments. If you select anitem in portrait mode a new Activity should get started with the selected item. In horizontal modeyour second Fragment should display the select item.22. ActionBar navigation with FragmentsFragments can also be used in combination with the ActionBar for navigation. For this your mainActivity needs to implement a TabListener which is responsible for moving between the tabs.The ActionBar allows to add tabs to it via the newTab() method. The following code shows such anActivity. It uses two Fragments, called DetailFragment and ImageFragment. At this point youshould be able to create these two Fragments yourself. package; import; import; import; import; import; import; import android.os.Bundle; public class MainActivity extends Activity { @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); // setup action bar for tabs ActionBar actionBar = getActionBar(); actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS); actionBar.setDisplayShowTitleEnabled(false); Tab tab = actionBar .newTab() .setText("First tab") .setTabListener( new MyTabListener<DetailFragment>(this, "artist", DetailFragment.class)); actionBar.addTab(tab); tab = actionBar .newTab() .setText("Second Tab") .setTabListener( new MyTabListener<ImageFragment>(this, "album", ImageFragment.class)); actionBar.addTab(tab); } public static class MyTabListener<T extends Fragment> implements TabListener { private Fragment mFragment; private final Activity mActivity; private final String mTag; private final Class<T> mClass; /** * Constructor used each time a new tab is created. * * @param activity * The host Activity, used to instantiate the fragment * @param tag converted by
  39. 39. * The identifier tag for the fragment * @param clz * The fragments Class, used to instantiate the fragment */ public MyTabListener(Activity activity, String tag, Class<T> clz) { mActivity = activity; mTag = tag; mClass = clz; } /* The following are each of the ActionBar.TabListener callbacks */ public void onTabSelected(Tab tab, FragmentTransaction ft) { // Check if the fragment is already initialized if (mFragment == null) { // If not, instantiate and add it to the activity mFragment = Fragment.instantiate(mActivity, mClass.getName()); ft.add(, mFragment, mTag); } else { // If it exists, simply attach it in order to show it ft.setCustomAnimations(android.R.animator.fade_in, R.animator.animationtest); ft.attach(mFragment); } } public void onTabUnselected(Tab tab, FragmentTransaction ft) { if (mFragment != null) { ft.setCustomAnimations(android.R.animator.fade_in, R.animator.test); ft.detach(mFragment); } } public void onTabReselected(Tab tab, FragmentTransaction ft) { } } }23. DDMS perspective and important views23.1. DDMS - Dalvik Debug Monitor ServerEclipse provides a perspective for interacting with your Android (virtual) device and your Androidapplication program. Select Window → Open Perspective → Other → DDMS to open this perspective. Itincludes several Views which can also be used independently and allows for example the application toplace calls and send SMS to the device. It also allows the application to set the current geo position andallows you to perform a performance trace of your application.23.2. LogCat ViewYou can see the log (including System.out.print() statements) via the LogCat view.23.3. File explorerThe file explorer allows to see the files on the Android simulator. converted by