Android Development: The Basics

Developing Android Apps: The Basics Mike Desjardins

Who Am I? • Independent Consultant - Ceres Logic Software Engineer at ELC Technologies • Professional Programmer 15 years • Mostly Java, lately lots of JRuby on Rails • Developed a several Android Apps in the Android Market Hi. • Haven’t done much iOS • Twitter: @cereslogicDeveloping for Android:The Basics 2

What’s In This Presentation? • What is Android? • Activities and Intents • Views • Permissions • Other Facilities • MarketplaceDeveloping for Android:The Basics 3

What is Android? • Open Handset Alliance - 80 Firms incl. Google, HTC, Dell, Motorola, LG, etc. • Custom Linux-based Kernel (forked) • Dalvik Virtual Machine • Apache Harmony • Native code can be written using the NDK (non-standard C Library, Bionic)Developing for Android:The Basics 4

Android’s Layers User applications: Contacts, phone, browser, etc. Application managers: windows, content, activities, telephony, location, notiﬁcations, etc. Android Runtime: Java via Dalvik VM Libraries: graphics, media, database, communications, browser engine, etc. Linux kernel, including device drivers Hardware device with speciﬁc capabilities such as GPS, camera, Bluetooth, etc.Abelson, W. Frank & Sen, Robi (2011) Unlocking Android, Second Edition (Fig. 1.4). Greenwich, CT: Manning Publications.Developing for Android:The Basics 5

What is Android: Dalvik VM • Created by Dan Bornstein • Register Based instead of Stack Based • Interprets .dex files .java .class Java .class .class .dex source Compiler file dx Compiler file files file code • Packaged w/ resources in .apk filesDeveloping for Android:The Basics 6

Versions in the Wild 95% of Android Devices are between version 2.1 (Éclair) and version 2.3 (Gingerbread) As of June 1, 2011 http://developer.android.com/resources/dashboard/platform-versions.htmlDeveloping for Android:The Basics 7

Versions in the Wild, cont. Skicast Free Skicast Pro TidecastDeveloping for Android:The Basics 8

Handsets in the Wild Skicast Free Skicast Pro TidecastDeveloping for Android:The Basics 9

What is “Rooting” ? • Processes in the Android system run under an unprivileged user account • Default user can’t access all of the ﬁlesystem, or some of the more interesting APIs (e.g., enabling mobile hotspot, setting CPU speed) • “Rooting” is ﬁnding back door shell access, and copying a program conceptually similar to su or sudo onto your phone. • Custom ROMs are something completely different.Developing for Android:The Basics 10

Development Environment • Eclipse + ADT is the “default” • Android SDK comes w/ command line tools and emulator (adb)Developing for Android:The Basics 11

Activities • Typical applications have (along with some other stuff) a collection of “Activities” • An Activity roughly corresponds to a screen • There is no correspondence among Process/VM/Applications/Activities • Class inheriting from android.app.Activity • Started by “Intents” (more on those later)Developing for Android:The Basics 12

I.e., Don’t Use Task Killers in a misguided attempt to extend battery life! Android Task Killer Apps = Worse Than UselessDeveloping for Android:The Basics 13

Activity Lifecycle Entire Lifetime - Between onCreate and onDestroy Visible Lifetime - Between onStart and onStop Foreground Lifetime - Between onResume and onPause Image: http://developer.android.com/images/activity_lifecycle.pngDeveloping for Android:The Basics 14

Demo Time!Developing for Android:The Basics 15

Views • Android allows you to be quite Model- View-Controllery • Views contain UI elements displayed on the screen by an Activity (controller) • Can be deﬁned in XML or programatically • Views are nested, topmost is a LayoutView • setContentView(viewId) or setContentView(view)Developing for Android:The Basics 16

Our Hello World Demo View <?xml version="1.0" encoding="utf‐8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/ res/android"     android:orientation="vertical"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     > <TextView       android:layout_width="fill_parent"      android:layout_height="wrap_content"      android:text="@string/hello"     /> </LinearLayout>Developing for Android:The Basics 17

Our Hello World Demo View <?xml version="1.0" encoding="utf‐8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/ res/android"     android:orientation="vertical"     android:layout_width="fill_parent" Which direction     android:layout_height="fill_parent" we’re ﬁlling     > <TextView       android:layout_width="fill_parent"      android:layout_height="wrap_content"      android:text="@string/hello"     /> </LinearLayout>Developing for Android:The Basics 18

Our Hello World Demo View <?xml version="1.0" encoding="utf‐8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/ res/android"     android:orientation="vertical"     android:layout_width="fill_parent" ﬁll_parent     android:layout_height="fill_parent"     > match_parent <TextView       android:layout_width="fill_parent"  wrap_content     android:layout_height="wrap_content"      android:text="@string/hello"     /> </LinearLayout>Developing for Android:The Basics 19

Our Hello World Demo View <?xml version="1.0" encoding="utf‐8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/ res/android"     android:orientation="vertical"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     > <TextView       android:layout_width="fill_parent"      android:layout_height="wrap_content"      android:text="@string/hello" what the???     /> </LinearLayout>Developing for Android:The Basics 20

Resources • Resources go into the res directory • Different Types: strings, layouts, drawables, arbitrary XML, styles, raw, etc. • Referenced in XML using identiﬁers preﬁxed with an at sign (@) followed by type • Handles / IDs end up in the mysterious “R” classDeveloping for Android:The Basics 21

R • Autogenerated by /* AUTO‐GENERATED FILE.  DO NOT MODIFY.  *  * This class was automatically generated by the  * aapt tool from the resource data it found.  It  * should not be modified by hand. Android’s compile  */ package com.cereslogic.demo01; tools public final class R {     public static final class attr { • Scans res folder, creates R in your     }     public static final class drawable {         public static final int icon=0x7f020000;     }     public static final class layout { gen folder w/ the         public static final int main=0x7f030000;     } same package name as your app.     public static final class string {         public static final int app_name=0x7f040001;         public static final int hello=0x7f040000;     } }Developing for Android:The Basics 22

Referring to Resources in Java package com.cereslogic.demo01; import android.app.Activity; import android.os.Bundle; public class Hello extends Activity {     /** Called when the activity is first created. */     @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.main);     } } Here’s an example!Developing for Android:The Basics 23

Let’s add a Button! <?xml version="1.0" encoding="utf‐8"?> <LinearLayout xmlns:android="http:// schemas.android.com/apk/res/android"     android:orientation="vertical"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     > <TextView       android:layout_width="fill_parent"      android:layout_height="wrap_content"      android:text="@string/hello" First we’ll add     /> <Button the button to      android:layout_height="wrap_content" our view in      android:layout_width="wrap_content"      android:text="@string/deliver_bacon" main.xml.      android:onClick="deliverBacon" /> </LinearLayout>Developing for Android:The Basics 24

Let’s add a Button! <?xml version="1.0" encoding="utf‐8"?> <resources>     <string name="hello">Hello World, Hello!</string>     <string name="app_name">AndroidPresentation</string>     <string name="deliver_bacon">Please Deliver Bacon!</string> </resources> add the string to values.xml Let’s try it out...Developing for Android:The Basics 25

Demo TimeDeveloping for Android:The Basics 26

Uh Oh! That’ll get you a one star review in the App Market. Let’s check logcat to see what went wrong...Developing for Android:The Basics 27

DOH! E/AndroidRuntime( 523): Uncaught handler: thread main exiting due to uncaught exception E/AndroidRuntime( 523): java.lang.IllegalStateException: Could not ﬁnd a method deliverBacon(View) in the activity E/AndroidRuntime( 523): at android.view.View$1.onClick(View.java:2016) E/AndroidRuntime( 523): at android.view.View.performClick(View.java:2344) E/AndroidRuntime( 523): at android.view.View.onTouchEvent(View.java:4133) . . . OOPS. We forgot to write the deliverBacon method in our Activity. It got called when onClick was ﬁred.Developing for Android:The Basics 28

Add a method for that... package com.cereslogic.androidpreso; import android.app.Activity; import android.os.Bundle; import android.util.Log; import android.view.View; public class Hello extends Activity {     /** Called when the activity is first created. */     @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.main);     }     public void deliverBacon(View view) {       Log.i("Demo App", "TODO: Figure Out How To Deliver Bacon!");     } } the view passed in is the button that was tappedDeveloping for Android:The Basics 29

Demo TimeDeveloping for Android:The Basics 30

Yeah... that was pretty lame. Bacon makes everything better, so...Developing for Android:The Basics 31

Yeah... that was pretty lame. Bacon makes everything better, so... ...let’s add a picture of bacon!Photo Credit: Shawn Zamechek (shawnzam), Licensed under Creative Commons (CC BY 2.0), http://www.ﬂickr.com/photos/shawnzam/31302636/Developing for Android:The Basics 31

Now Things Start To Get Ugly • We are supporting devices with multiple screen densities. • Good News: Android provides a way to support multiple screen densities • Bad News: We will probably want to include four copies of our bacon picture in our appDeveloping for Android:The Basics 32

Screen Densities • Android currently generalizes screens into four categories of screen density • LDPI (low) - QVGA, 120dpi, ~240x320 • MDPI (medium) - HVGA, 160dpi, ~320x480 • HDPI (high) - WVGA, 240dpi, ~480x800 • XHDPI (xtra high) - ? 320dpi, Added in Android 2.3 (Gingerbread)Developing for Android:The Basics 33

Bacon should Fill the Screen! • We want Bacon to ﬁll the width of the screen in HIGH DEFINITION, so we will make four sizes LDPI MDPI 320x240 HDPI 480x360 XHDPI 640x480Developing for Android:The Basics 34

Add Bacon... <?xml version="1.0" encoding="utf‐8"?> <LinearLayout xmlns:android="http://schemas.android.com/ apk/res/android"     android:orientation="vertical"     android:layout_width="fill_parent"     android:layout_height="fill_parent"     > <TextView       android:layout_width="fill_parent"      android:layout_height="wrap_content"      android:text="@string/hello"     />   <Button      android:layout_height="wrap_content"      android:layout_width="wrap_content"      android:text="@string/deliver_bacon"      android:onClick="deliverBacon" /> <ImageView      android:layout_height="wrap_content"       android:layout_width="fill_parent"      android:src="@drawable/bacon"/> </LinearLayout> Now let’s try that out...Developing for Android:The Basics 35

Bacon TimeDeveloping for Android:The Basics 36

Meh. That’s still pretty lame We could make the bacon only appear when the button is clicked... 1 Make the bacon’s default state hidden: visible, invisible, or gone <ImageView      android:visibility="invisible"      android:layout_height="wrap_content"       android:layout_width="fill_parent"      android:src="@drawable/bacon"/>Developing for Android:The Basics 37

Meh. That’s still pretty lame We could make the bacon only appear when the button is clicked... 2 Put an ID on our bacon: The @+id in our XML is special magic that causes the Android build tools to generate an handle w/ an ID for the view in the R object <ImageView      android:id="@+id/bacon_image"      android:visibility="invisible"      android:layout_height="wrap_content"       android:layout_width="fill_parent"      android:src="@drawable/bacon"/>Developing for Android:The Basics 38

Meh. That’s still pretty lame We could make the bacon only appear when the button is clicked... 3 Wire up the Button listener to do something:     public void deliverBacon(View view) {       ImageView i = (ImageView)findViewById(R.id.bacon_image);       if (i.getVisibility() == View.INVISIBLE) {         i.setVisibility(View.VISIBLE);       } else {         i.setVisibility(View.INVISIBLE);       }     } Let’s try that out!Developing for Android:The Basics 39

Blinky Bacon TimeDeveloping for Android:The Basics 40

ListViews • Probably the most common UI Element is a ListView • Allows you to scroll through a selection of items and choose one • Next we’ll add a list of bacon-related treats to our app!Developing for Android:The Basics 41

Create a List of Treats 1 Put our list entries into strings.xml <?xml version="1.0" encoding="utf‐8"?> <resources>     <string name="hello">Hello World, Hello!</string>     <string name="app_name">AndroidPresentation</string>     <string name="deliver_bacon">Please Deliver Bacon!</string>     <string name="show_bacon_treats">Show me treats!</string>     <string name="bacon_treat_list">Bacon Treat List</string>     <string name="bacon_plain">Bacon (Plain)</string>     <string name="bacon_lettuce_tomato_sandwich">Bacon, Lettuce, Tomato sandwich</string>     <string name="bacon_and_eggs">Bacon and Eggs</string>     <string name="bacon_cheeseburger">Bacon Cheeseburger</string>     <string name="bacon_bits">Bacon Bits</string>     <string name="bacon_ice_cream">Bacon Ice Cream</string>     <string name="bacon_chewing_gum">Bacon Chewing Gum</string>     <string name="bacon_lollipop">Bacon Lollipop</string> </resources>Developing for Android:The Basics 42

Create a List of Treats, cont. 2 Create a TextView to hold our list entries <?xml version="1.0" encoding="utf‐8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android"   android:layout_width="fill_parent"   android:layout_height="wrap_content"   android:textSize="24.0dip"   android:padding="4.0dip"   android:id="@+id/empty_text_view"> </TextView> Wait... a TextView? Don’t you mean ListView or something? Nope - this is what each list item will contain.Developing for Android:The Basics 43

Create a List of Treats, cont. Create a new Activity class that inherits 3 from ListActivity public class BaconTreats extends ListActivity {   @Override   protected void onCreate(Bundle savedInstanceState) {       super.onCreate(savedInstanceState);       //setContentView(R.layout.treat_list); unneeded ListActivity provides a default              ArrayAdapter<String> aa = new ArrayAdapter<String>(this,R.layout.empty);       aa.add(getResources().getString(R.string.bacon_plain));       aa.add(getResources().getString(R.string.bacon_and_eggs));       aa.add(getResources().getString(R.string.bacon_bits));       aa.add(getResources().getString(R.string.bacon_cheeseburger));       aa.add(getResources().getString(R.string.bacon_chewing_gum));       aa.add(getResources().getString(R.string.bacon_ice_cream));       aa.add(getResources().getString(R.string.bacon_lettuce_tomato_sandwich));       aa.add(getResources().getString(R.string.bacon_lollipop));       setListAdapter(aa);   } } Converts objects to things appearing in ListViewDeveloping for Android:The Basics 44

Create a List of Treats, cont. Add the new Activity to the Manifest 4 (hey waitaminute - what’s a Manifest?) <?xml version="1.0" encoding="utf‐8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"       package="com.cereslogic.androidpreso"       android:versionCode="1"       android:versionName="1.0">     <application android:icon="@drawable/icon" android:label="@string/app_name">         <activity android:name=".Hello"                   android:label="@string/app_name">             <intent‐filter>                 <action android:name="android.intent.action.MAIN" />                 <category android:name="android.intent.category.LAUNCHER" />             </intent‐filter>         </activity>         <activity android:name=".BaconTreats"                   android:label="@string/bacon_treat_list">         </activity>     </application> </manifest>Developing for Android:The Basics 45

Create a List of Treats, cont. 4 So... what is a Manifest? • AndroidManifest.xml in the root directory of the project. • Describes Activities in your project and any intents that should activate them (hey waitaminute - what’s an Intent? We’ll get to that in a minute) • Describes application permissions, version, name, req’d API version, other stuffDeveloping for Android:The Basics 46

ListActivity is ready • We’ve created our ListActivity, now how do we get to it? • We’ll add an ugly little button in our Main screen that launches the list: <Button      android:layout_height="wrap_content"      android:layout_width="wrap_content"      android:text="@string/show_bacon_treats"      android:onClick="showBaconTreats" /> Now we need to implement the showBaconTreats method...Developing for Android:The Basics 47

showBaconTreats public class Hello extends Activity {     /** Called when the activity is first created. */ Hey - there’s one of those Intent things     @Override     public void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.main);     } again...     public void showBaconTreats(View view) {       Intent intent = new Intent(Intent.ACTION_VIEW);       intent.setComponent(         new ComponentName("com.cereslogic.androidpreso","com.cereslogic.androidpreso.BaconTreats")       );       startActivity(intent);     }          public void deliverBacon(View view) {       ImageView i = (ImageView)findViewById(R.id.bacon_image);       if (i.getVisibility() == View.INVISIBLE) {         i.setVisibility(View.VISIBLE);       } else {         i.setVisibility(View.INVISIBLE);       }     } }Developing for Android:The Basics 48

Et Voila!Developing for Android:The Basics 49

Intents • In some ways, Android resembles a Service- oriented Architecture (SOA) • An Intent represents the user’s desire to accomplish something • An app can create an Intent without knowing or caring what Activity will receive it • Applications create Intent Filters in their manifests, indicating Activities (or other things like BroadcastReceivers) that would like to be notiﬁed of IntentsDeveloping for Android:The Basics 50

Intent Resolution • Two types of Intents: • Explicit - identifies a Component Name (a specific Activity class) to be started. This is how we launched our ListActivity earlier • Implicit - does not name a target Activity, instead identifies an action, a category, and data and/or data type • Typical “Actions”: ACTION_VIEW, ACTION_DIAL, ACTION_EDIT, etc.Developing for Android:The Basics 51

Examples of Implicit Intents • Data is given in URL format: scheme://data • ACTION_VIEW contacts://people/1 shows the contact who’s identifier is 1. • ACTION_DIAL tel://2075551212 shows the dialer with 207-555-1212 filled in. • Normally the data type is inferred by the scheme, but you can force it to a specific MIME type in the Intent constructor • “Categories” are sometimes used to further refine which Activities may be launchedDeveloping for Android:The Basics 52

What if more than one intent will work? • If more than one Activity is registered to receive an intent, Android will ask the user which Activity they want to launch • This is how people build things like alternate dialers or text messaging appsDeveloping for Android:The Basics 53

Declaring supported Intents • If an Activity wants to make itself available to receive speciﬁc Intents, it declares them in its application’s Manifest <?xml version="1.0" encoding="utf‐8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"       package="com.cereslogic.androidpreso"       android:versionCode="1"       android:versionName="1.0"> Allows our     <application android:icon="@drawable/icon" android:label="@string/app_name">         <activity android:name=".Hello"                   android:label="@string/app_name"> app to be a             <intent‐filter>                 <action android:name="android.intent.action.MAIN" />                 <category android:name="android.intent.category.LAUNCHER" /> target for             </intent‐filter>         </activity>         <activity android:name=".BaconShare" photo                   android:label="@string/bacon_share">             <intent‐filter> sharing                 <action android:name="android.intent.action.ACTION_SEND" />                 <data android:mimeType="image/png" />                 <category android:name="android.intent.category.DEFAULT" />             </intent‐filter>                           </activity>     </application> </manifest>Developing for Android:The Basics 54

Declaring supported Intents • First Activity launched by your App gets the MAIN/LAUNCHER intent: <?xml version="1.0" encoding="utf‐8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"       package="com.cereslogic.androidpreso"       android:versionCode="1"       android:versionName="1.0">     <application android:icon="@drawable/icon" android:label="@string/app_name">         <activity android:name=".Hello"                   android:label="@string/app_name">             <intent‐filter>                 <action android:name="android.intent.action.MAIN" />                 <category android:name="android.intent.category.LAUNCHER" />             </intent‐filter>         </activity>         <activity android:name=".BaconShare"                   android:label="@string/bacon_share">             <intent‐filter>                 <action android:name="android.intent.action.ACTION_SEND" />                 <data android:mimeType="image/png" />                 <category android:name="android.intent.category.DEFAULT" />             </intent‐filter>                           </activity>     </application> </manifest>Developing for Android:The Basics 55

Permissions • To use some of the facilities in the device, you need to declare that you will use them in the Manifest. • The user is informed of these permissions when he or she downloads your application. • Examples: Location (Fine and Coarse), WiFi state, Network state, Call, Camera, Internet, Send/Receive SMS, Read ContactsDeveloping for Android:The Basics 56

Common IdiomsDeveloping for Android:The Basics 57

Common Idioms • Android makes extensive use of callbacks • Example of selecting an item from a ListView, passing that value to the next activity, and exiting: listView.setOnItemClickListener(new OnItemClickListener() {   public void onItemClick(AdapterView<?> parent, View view, int position, long id) {     selected = (String)myListAdapter.getItem(position);     Intent intent = new Intent(Intent.ACTION_VIEW);     intent.setComponent(       new ComponentName("com.cereslogic.androidpreso",                         "com.cereslogic.androidpreso.NextActivity")     );     intent.putExtra("selected", selected); // avail to NextActivity via getIntent()     startActivity(intent);     finish();  // called when we don’t want to come back here when user presses back.   } });Developing for Android:The Basics 58

Common Idioms • Separate “Handler” with a progress dialog when asynchronous stuff may take a while • If you don’t do this, Android may just decide to kill your applicationDeveloping for Android:The Basics 59

Time-consuming Async Tasks private class BaconFryingTask extends AsyncTask<BaconInputType, BaconProgressType, BaconResultType> {   @Override   protected BaconResultType doInBackground(BaconInputType... params) {     Bacon bacon = BaconFactory.createInstance(params[0]);     bacon.sizzle(Bacon.CRISPY);            publishProgress(new BaconProgressType(50));     bacon.flip();     bacon.sizzle(Bacon.CRISPY);            publishProgress(new BaconProgressType(100));     return bacon;   }   @Override   protected void onProgressUpdate(BaconProgressType... params) {     Integer progress = params[0].getPercentCooked();     setProgressPercent(progress);       }   @Override   protected void onPostExecute(BaconResultType result) {     Log.d(“BaconFryingTask”, “The Bacon is ready!”);   } } To kick off the task... new BaconFryingTask().execute(params);Developing for Android:The Basics 60

Demo Time!Developing for Android:The Basics 61

Code for the Bad Bacon Joke public class BadBaconJoke extends Activity {   private ProgressDialog progressDialog;   @Override   public void onCreate(Bundle savedInstanceState) {     super.onCreate(savedInstanceState);     this.progressDialog =       ProgressDialog.show(this, "working...",                          "Some pancakes, eggs, and bacon walk into a bar. Bartender looks at them and says...");      new PunchlineTask().execute();   }     private class PunchlineTask extends AsyncTask<Void, Void, String> {     @Override     protected String doInBackground(Void... params) {       try {         Thread.sleep(8000);       } catch (InterruptedException e) { /* Don’t ever do this */ }        return "...hey! We dont serve breakfast here!";     }     @Override     protected void onPostExecute(String result) {       progressDialog.dismiss();       new AlertDialog.Builder(BadBaconJoke.this)           .setMessage(result).setCancelable(false).setTitle("Punchline")           .setPositiveButton("Groan", new DialogInterface.OnClickListener() {             public void onClick(DialogInterface dialog, int which) {               Toast.makeText(getApplicationContext(), "Sorry.", Toast.LENGTH_LONG).show();             }           }).show();     }   } }Developing for Android:The Basics 62

BroadcastReceiver • Used for receiving events. Intended for short “trigger” style events, not long running activities (use Services for those) • Examples: Incoming Phone Call, Text Message • Registered using Intent Filters, just like Activities • No View associated with them • Can be registered statically in the manifest, or at runtime • Instance goes away when you’re ﬁnished processing • Ordered or (more typically) UnorderedDeveloping for Android:The Basics 63

Trivial BroadcastReceiver Example Sorry, no Bacon this time... public class WiFiChangeReceiver extends BroadcastReceiver {   private final static String TAG = "WiFiChangeReceiver";     @Override Receiver   public void onReceive(Context context, Intent intent) {     Log.d(TAG, "In onReceive."); class     doSomethingAsynchronouslyInTheBackground();   } } <receiver android:name="com.cereslogic.demo.WiFiChangeReceiver"            android:enabled="true">   <intent‐filter>     <action android:name="android.net.wifi.WIFI_STATE_CHANGED" /> Manifest </intent‐filter> </receiver>Developing for Android:The Basics 64

(Demo if there is time)Developing for Android:The Basics 65

Services • Long-running background processes • Need to be started and stopped by an Application (e.g., in a BroadcastReceiver), but otherwise run independently of the applications with which they’re associated • “Foreground” services are less likely to be killed by the OS • Great way to drain batteries • Big sloppy half-hearted example on the next slideDeveloping for Android:The Basics 66

Service Example public class LocalService extends Service {   private NotificationManager notificationManager;   private int NOTIFICATION = R.string.local_service_started;   @Override   public void onCreate() {     notificationManager = (NotificationManager)getSystemService(NOTIFICATION_SERVICE);     showNotification();   }   @Override   public int onStartCommand(Intent intent, int flags, int startId) {     // We want this service to continue running until it is explicitly     // stopped, so return sticky.     return START_STICKY;   }   @Override   public void onDestroy() {     notificationManager.cancel(NOTIFICATION);     Toast.makeText(this, R.string.local_service_stopped, Toast.LENGTH_SHORT).show();   }   private void showNotification() {     CharSequence text = getText(R.string.local_service_started);     Notification notification = new Notification(R.drawable.notification_icon, text, System.currentTimeMillis());     PendingIntent contentIntent = PendingIntent.getActivity(this, 0, new Intent(this, AnActivity.class), 0);     notification.setLatestEventInfo(this, getText(R.string.local_service_label), text, contentIntent);     notificationManager.notify(NOTIFICATION, notification);   } } Kick it off like this... context.startService(new Intent(context, LocalService.class));Developing for Android:The Basics 67

Location Services • A little weird to program for • Can’t just ask the system “hey, where am I right now?” • Two Options: • Last known location • Sample location at rate X, and register to be notiﬁed when location changes by more than X from the previous locationDeveloping for Android:The Basics 68

Very Simple Location Example public class LocationClient implements LocationListener {   private static final Long MIN_UPDATE_INTERVAL = 1000L;   private static final float MIN_DISTANCE_SENSITIVITY = 100.0f;   private LocationManager locationManager;   private Location location = null;   public void determineLocation() {     this.locationManager = (LocationManager)this.getSystemService(LOCATION_SERVICE);     String bestProvider = this.getBestLocationProvider();     this.locationManager.requestLocationUpdates(bestProvider, MIN_UPDATE_INTERVAL, MIN_DISTANCE_SENSITIVITY, this);   }   private String getBestLocationProvider() {     Criteria criteria = new Criteria();     criteria.setAccuracy(Criteria.ACCURACY_COARSE);     criteria.setAltitudeRequired(false);     criteria.setBearingRequired(false);     criteria.setSpeedRequired(false);     String bestProvider = this.locationManager.getBestProvider(criteria, true);     return bestProvider;   }   // Required by LocationListener...   public void onLocationChanged(Location location) {     this.location = location;     logLocation(location);     this.locationManager.removeUpdates(this);   }   public Location getLocation() {     return this.location;   } }Developing for Android:The Basics 69

Android Market • No wait to publish apps - upload in the developer console, and it’s available to everybody. • Buyer’s currency • In-app purchases • Google Checkout for purchases, 2.9% discount rate • Google’s cut of app price: 30%Developing for Android:The Basics 70

Developer ConsoleDeveloping for Android:The Basics 71

Developer Console stats (earlier in presentation) user comments error reports in-apppurchasesDeveloping for Android:The Basics 72

Developer Console - Error ReportsDeveloping for Android:The Basics 73

Developer Console - Error ReportsDeveloping for Android:The Basics 74

Questions?Developing for Android:The Basics 75

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Android Development: The Basics

by Mike Desjardins on Jun 27, 2011

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Android Development: The Basics — Presentation Transcript