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A Deep Dive into Open Source Android Development


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The increasing popularity of the Android platform over the past two years has encouraged many talented developers to contribute. Developers no longer need to invent their own wheels from scratch. Instead, many open source tools and libraries are becoming available for Android developers. In this talk we will take a deep dive into Android programming and how developers can leverage open source tools to bootstrap their Android apps. We will also talk about how developers can contribute back to the open source community.

A Deep Dive into Open Source Android Development

  1. 1. A Deep Dive into Open Source Android Development David Wu @wuman Taipei Google Technology User Group (2013/01/02) Taipei Open Source Software User Group (2012/12/18)元智大學資工學系 開放源碼於行動終端之發展講座 (2012/12/07) 1
  2. 2. 2
  3. 3. Overview• Why use open source?• Popular open source Android libraries• Why open source?• How to open source• Conclusion 3
  4. 4. Why use open source? 4
  5. 5. Better Quality• Developed by many passionate developers• Innovation and enhancements over time• Improvements and bug fixes by more people• Closest to user needs 5
  6. 6. Freedom• Make custom changes to tailor to own needs• Good open source software usually adheres to open standards and promotes interoperability 6
  7. 7. Learn from the Masters• Open source developers are usually good at what they do• The fastest way to improve is to learn from reading their code• Discussions are usually carried out in the open via mailing lists 7
  8. 8. Not Possible Otherwise• It is much harder to develop an Android app without using open source software • Platform compatibility • UI compatibility 8
  9. 9. Android appdevelopment is NOT easy! 9
  10. 10. Version Codename API Distribution Eclair & older 1.5 Cupcake 3 0.1% Jelly Bean 1.6 Donut 4 0.3% Froyo 2.1 Eclair 7 2.7% 2.2 Froyo 8 10.3% Ice Cream Sandwich 2.3 - 2.3.2 9 0.2% Gingerbread2.3.3 - 2.3.7 10 50.6% 3.1 12 0.4% Honeycomb 3.2 13 1.2% Gingerbread Honeycomb Ice Cream4.0.3 - 4.0.4 15 27.5% Sandwich 4.1 16 5.9% Jelly Bean 4.2 17 0.8% Apps targeting the widest audience need to care about platform compatibility 10
  11. 11. UI Requirements for Featured Apps• Follow Android Design guidelines • Navigation • Action Bar• Use common UI patterns and icons 11
  12. 12. Action Bar Incompatibility• Before 3.0, there was no common pattern or API for in-app navigation.• Action Bar API and pattern guidelines (tablet-only) are introduced in ICS.• Additional API changes for the phone are introduced in Jelly Bean. 12
  13. 13. Theme Incompatibility• There is not a common cross-platform default theme for developers to derive from. 13
  14. 14. Common UI Pattern Implementations• Some common UI patterns are not provided as part of the Android framework. • Pull-to-refresh ListView • Sliding Drawer Menu (ViewDeck) 14
  15. 15. Common Tools and Usage Patterns• Some common tools and usage patterns are not provided as part of the Android framework. • LRU cache that persists to disk • Image loading with cache support • Logging and user feedback support 15
  16. 16. Popular Open Source Libraries 16
  17. 17. UI and Compatibility 17
  18. 18. ActionBarSherlock 18
  19. 19. Action Bar General Layout• App icon and “up” affordance• View switch control• Action buttons• Action overflow 19
  20. 20. Split Action Bar• Main action bar• Top bar via tabs or spinner• Bottom bar with action buttons and overflow 20
  21. 21. Contextual Action Bars 21
  22. 22. HoloEverywhere• Back ports the Holo themes from Jelly Bean to Eclair and above 22
  23. 23. NineOldAndroids• Back ports the android.animation.* API from Honeycomb to all previous platforms• Drawing vs. View properties ObjectAnimator.ofFloat(myObject, "translationY", -myObject.getHeight()).start(); 23
  24. 24. UnifiedPreference 24
  25. 25. Android Support Package• Back ports multi-pane Fragment support from Honeycomb to Donut 25
  26. 26. Android Support Package• Includes ViewPager, PagerTitleStrip, PagerTabStrip implementations 26
  27. 27. Android Support Package• Back ports all Notification features from Jelly Bean to Donut 27
  28. 28. Android Support Package• Back ports asynchronous background Loader support from Honeycomb to Donut• Includes implementation for a memory-based LruCache 28
  29. 29. Android-MenuDrawer 29
  30. 30. Android-PullToRefresh 30
  31. 31. Polaris 31
  32. 32. Crouton 32
  33. 33. Android-Query• Enables easier UI manipulation via method chaining AQuery aq = new AQuery(view); .image(R.drawable.icon) .visible() .clicked(this, "someMethod"); .text(content.getPname()); .text(FormatUtility.relativeTime( System.currentTimeMillis(), content.getCreate())) .visible(); .text(content.getDesc()) .visible(); 33
  34. 34. Caching andNetworking 34
  35. 35. DiskLruCache• Back ports the DiskLruCache from Ice Cream Sandwich to all versions of Android 35
  36. 36. TwoLevelLruCache• A two-level LRU cache composed of • first level memory-based LruCache • second level disk-based DiskLruCache 36
  37. 37. AndroidImageLoader• Asynchronous image loading • Images are downloaded and saved to TwoLevelLruCache via a pool of background threads • Supports Bitmap transformations 37
  38. 38. HttpResponseCache• Back ports the persistent HttpResonseCache from Ice Cream Sandwich to all versions of Android• Provides transparent and automatic persistent caching of HTTP and HTTPS requests that use the HttpUrlConnection class 38
  39. 39. HTTP-Request• Provides a simpler and easier interface to HttpURLConnection• Uses method chaining HttpRequest.get("").receive(System.out); 39
  40. 40. Concurrency andCommunication 40
  41. 41. Tape• Provides a persistent task queue ServerClient UI TaskQueue peek() remove() add() UploadTask UploadTask Service 41
  42. 42. Otto• An event bus forked from EventBus of Google Guava targeting the Android platform Publish Subscribe Fragment Fragment Fragment Bus Fragment Service Activity 42
  43. 43. Data Representation and Processing 43
  44. 44. GSON• POJO to JSON bi-directional conversion• Built-in serializers and deserializers for primitive data types• Supports extensions for complex objects 44
  45. 45. Jackson JSON Processor• Streaming JSON parser and serializer• Supposedly faster than the built-in ones 45
  46. 46. Json-Path• XPath- and jQuery-like selector for JSON { "store": {     "book": [       { "category": "reference",         "author": "Nigel Rees",         "title": "Sayings of the Century",         "price": 8.95       },       { "category": "fianceection",         "author": "Evelyn Waugh",         "title": "Sword of Honour", String author =, "$[1].author");         "price": 12.99,         "isbn": "0-553-21311-3"       }     ],     "bicycle": {       "color": "red",       "price": 19.95     }   } } 46
  47. 47. jOOX - Java Object Oriented XML• XML manipulative parser with selector syntax• XML document creation 47
  48. 48. JSoup• HTML parser for Java using jQuery-like selector syntax• Manipulates HTML elements, attributes and text• Prettifies HTML 48
  49. 49. OrmLite• ORM library that persists POJO to SQLite databases public class SimpleData { ! @DatabaseField(generatedId = true) ! int id; ! @DatabaseField(index = true) ! String string; ! @DatabaseField ! long millis; ! @DatabaseField ! Date date; ! @DatabaseField ! boolean even; ! SimpleData() { ! ! // needed by ormlite ! } ! public SimpleData(long millis) { ! ! = new Date(millis); ! ! this.string = (millis % 1000) + "ms"; ! ! this.millis = millis; ! ! this.even = ((millis % 2) == 0); ! } } 49
  50. 50. Google Guava• Many utilities to make Java development easier 50
  51. 51. Dependency Injection 51
  52. 52. AndroidAnnotations• Runtime injection of Android views, extras, system services, resources, etc.• Method annotation to indicate which thread to run in• Method annotation to bind event listeners to events 52
  53. 53. RoboGuice• Runtime injection of Android views, system services, resources, POJO, etc. 53
  54. 54. Dagger• Compile-time dependency injection (binding validation) for Android• Not as feature-rich as other dependency injection frameworks but much faster• API very similar to Google Guice † 54
  55. 55. Testing 55
  56. 56. Android Test Framework• Built-in Android Test Project support• Use AndroidTestCase to test non-visual components• Use Instrumentation to control visual parts of an application• Command line monkey tool to send random events to device 56
  57. 57. Robotium• Black-box testing framework for Android• Improved readability of test cases compared to standard Instrumentation tests• Handles multiple Android activities 57
  58. 58. Robotium // Check that we have the right activity solo.assertCurrentActivity("wrong activiy", SimpleActivity.class); // Click a button which will start a new Activity // Here we use the ID of the string to find the right button solo.clickOnButton(solo.getString(R.string.button1)); // Validate that the Activity is the correct one solo.assertCurrentActivity("wrong activiy", SimpleListActivity.class); // Open the menu solo.sendKey(Solo.MENU); solo.clickOnText("Preferences"); solo.clickOnText("User"); solo.clearEditText(0); Assert.assertTrue(solo.searchText("")); solo.enterText(0, "http//"); Assert.assertTrue(solo.searchText("http//")); solo.goBack(); 58
  59. 59. Mochito• Android mocking framework• API makes mocking tests very readable public void makePurchase(CreditCardManager creditCard) { if (creditCard.getCardType() == CREDIT_CARD_VISA) { creditCard.makePurchase(500); } } public void testMasterCardTransaction() { CreditCardManager creditCard = Mockito.mock(CreditCardManager.class); Mockito.when(creditCard.getCardType()) .thenReturn(CREDIT_CARD_MASTER); makePurchase(creditCard); Mockito.verify(creditCard).getCardType(); Mockito.verifyNoMoreInteractions(creditCard); } 59
  60. 60. Robolectric• Allows JVM unit testing with the JUnit4 framework• Reduces testing time from minutes to seconds• Intercepts Android class loading and forward method bodies to shadow objects 60
  61. 61. Robolectric // Test class for MyActivity @RunWith(RobolectricTestRunner.class) public class MyActivityTest { private Activity activity; private Button pressMeButton; private TextView results; @Before public void setUp() throws Exception { activity = new MyActivity(); activity.onCreate(null); pressMeButton = (Button) activity.findViewById(; results = (TextView) activity.findViewById(; } @Test public void shouldUpdateResultsWhenButtonIsClicked() throws Exception { pressMeButton.performClick(); String resultsText = results.getText().toString(); assertThat(resultsText, equalTo("Testing Android Rocks!")); } } 61
  62. 62. User Feedback 62
  63. 63. ACRA• Sends a detailed bug or crash report to Google Docs 63
  64. 64. BugSense/Crittercism• Collects bug and crash reports• Generates analytics for crash reports• Supports fix versioning and notifications 64
  65. 65. Google Analytics for Android• Collect user engagement data and generate real time analytics• Demo 65
  66. 66. Bootstrap Project Generator 66
  67. 67. Android Bootstrap• Includes a full working implementation of • Android support package • android-maven-plugin • RoboGuice • ActionBarSherlock • http-request • GSON • Robotium • API on 67
  68. 68. AndroidKickstartR• Includes a full working implementation of • Android support package • android-maven-plugin • AndroidAnnotations • ActionBarSherlock • NineOldAndroids • ACRA 68
  69. 69. Tools 69
  70. 70. Android Asset Studio• Demo 70
  71. 71. Subtle Patterns• Collection of free tilable textured patterns• Demo 71
  72. 72. Charles• HTTP proxy that enables developers to view all HTTP/HTTPS traffic between the device and the Internet 72
  73. 73. Others 73
  74. 74. More Detailed Listing• App Dev Wiki• The Ultimate Android Library http://• AppBrain Android Developer Tools http:// 74
  75. 75. Why open source? 75
  76. 76. Better App Quality• Normally for various practical reasons we don’t open source the entire app• Open source useful components within the app into a library• More debugging for you• The process of open sourcing forces you to rethink your architecture critically 76
  77. 77. Reciprocity• A way to give back to the community• Feels good 77
  78. 78. Portfolio Buildup• GitHub, not LinkedIn 78
  79. 79. Grow Faster• The more you engage in the open source community, the faster you learn and grow as a tech professional.• The process of open sourcing encompasses almost all areas of software development. 79
  80. 80. Better World• What goes around comes around• The template for this Keynote presentation is derived from an open source project! 80
  81. 81. How to Open Source 81
  82. 82. DisclaimerWhat follows is based on the presentation “EffectiveOpen Source” given by Jake Wharton andadditionally, a more elaborate presentation based onmy own experiences. 82
  83. 83. Component Identification• Identify the part of your app that can be extracted out as an isolated, reusable component.• The component should serve to do a focused task very well. 83
  84. 84. Code Abstraction• Extract the component into a separate package or module and expose only via a small set of public API.• This is kind of like refactoring. The app should continue to work as expected and the module should be treated just like an external dependency.• Reiterate the refactoring step several times until • the exposed public API is minimal and clean • the client code has good readability 84
  85. 85. Library Project Directory Structure• Make the module either an independent Java library project or an Android library project depending on whether Android resources are needed in the library.• Follow a common directory structure as defined in a maven archetype: • org.apache.maven.archetypes/maven- archetype-quickstart • 85
  86. 86. Android Library Project Directory Structure library/ Android Library project test/ Android Test project samples/ Samples project (Android project) README Project’s readme LICENSE Project’s license Notices and attributions required by NOTICE libraries that the project depends on 86
  87. 87. Java Library Project Directory Structure library/ Java library project library/src/main/java/ Java library sources library/src/test/java/ Test sources samples/ Samples project (Android project) README Project’s readme LICENSE Project’s license Notices and attributions required by NOTICE libraries that the project depends on 87
  88. 88. Include Tests• Good libraries are always bundled with tests. It gives people confidence and ensures quality.• Tests are never enough. Write as many as you can think of.• Ensure all the tests are passed. 88
  89. 89. Code Quality and Style• Standardize code conventions.• Enforce coding style at compile time by using Checkstyle for Java.• This ensures that future patches have a consistent coding style. 89
  90. 90. Inclusion of Examples• Add at least one or more working examples.• Separate examples to showcase a specific aspect of the library. 90
  91. 91. Documentation• Make sure all exposed public APIs have documentation that follow the javadoc syntax.• Ensure that a javadoc jar is generated for each release. This is best achieved via the maven- javadoc-plugin. 91
  92. 92. README• Write a README that follows the Markdown syntax.• It should include the following sections: • project description • how to obtain the library • snippets of quick start sample code • external dependencies • license information 92
  93. 93. Git Ignore• Always include a .gitignore file to keep the source tree clean. There are many samples online.• In general exclude these files: • IDE-specific files (Eclipse.gitignore) • OS-specific files (OSX.gitignore) • Android outputs and binaries (Android.gitignore) • Java compiled classes and package files (Java.gitignore) 93
  94. 94. Build Management Tool• Use a build management tool to help people painlessly build your code without needing to know much about the library.• Most Android people use Maven.• Write the configuration file that works with your build management tool. In the case of Maven it should be pom.xml. 94
  95. 95. Maven• Install the latest android-maven-plugin.• The packaging for the library project should be either jar or apklib, depending on whether your library is a Java project or an Android Library project.• The packaging for the samples project should be apk. 95
  96. 96. Build with Maven• Make sure the build management tool builds your project correctly.• For Maven, you should be able to run the following without errors: $  mvn  clean  install 96
  97. 97. Continuous Integration• Setup continuous integration. The simplest open source service is Travis. Have your GitHub repository linked to Travis by activating a hook.• Write the configuration file .travis.yml. language:  java                                                                                                                                   notifications:    email:  false before_install:    -­‐  wget­‐sdk_r20.0.3-­‐linux.tgz    -­‐  tar  -­‐zxf  android-­‐sdk_r20.0.3-­‐linux.tgz    -­‐  export  ANDROID_HOME=~/builds/username/projectName/android-­‐sdk-­‐linux    -­‐  export  PATH=${PATH}:${ANDROID_HOME}/tools:${ANDROID_HOME}/platform-­‐tools    -­‐  android  list  sdk      -­‐  android  update  sdk  -­‐-­‐filter  1,2,3  -­‐-­‐no-­‐ui  -­‐-­‐force 97
  98. 98. Site Setup• Setup a project web site.• If you’re lazy and wish to use just the GitHub README, then the best alternative is the DocumentUp service.• Configure Travis indicator and Google Analytics tracking for the web site. <script  src=""></script> <script> DocumentUp.document({ repo:  "wuman/AndroidImageLoader", name:  "AndroidImageLoader", twitter:  ["wuman"], issues:  true, travis:  true, google_analytics:  "UA-­‐4156099-­‐13" }); </script> 98
  99. 99. Issue Management• GitHub has built-in issue management support, although many developers consider Google Code to be better for issue management.• Quick triage of issues 99
  100. 100. Mailing List• Setup a Google Groups mailing list for the project so that people can have a place for discussion. 100
  101. 101. Downloadable Published Packages• Always make the released packages (usually jars) available for download. Use the com.github.github/downloads-maven-plugin.• If your library has dependencies, it is best to release a separate jar with dependencies using the maven-assembly-plugin. 101
  102. 102. Release to Sonatype and Maven Central• Sonatype provides an OSS repository hosting service for free. You can deploy snapshots and releases so that they are also synced periodically to Maven Central.• Follow their detailed guide.• In the end you should be able to deploy your project with: $  mvn  clean  package  release:prepare $  mvn  release:perform 102
  103. 103. Promote the Library• Write a blog post to talk about the motivations behind the project, technical explanations and sample code snippets. Also direct readers to the project page.• Publish your project everywhere: social networks, related communities, etc.• Encourage people to use and contribute.• Ask for feedback. 103
  104. 104. Join the Android Community• Follow these smart people on Google+: • Googlers • Chet Haase, Dan Morrill, Dianne Hackborn, Jean-Baptiste Quéru, Jeff Sharkey, Kirill Grouchnikov, Matias Duarte, Patrick Dubroy, Reto Meier, Roman Nurik, Romain Guy, Tor Norbye, Xavier Ducrohet • Android Developers • Community • Bob Lee, Chris Banes, Cyril Mottier, David Wu (shameless plug), Eric Burke, Jake Wharton, Jesse Wilson, Lars Vogel, Steve Kondik 104
  105. 105. Conclusion 105
  106. 106. 106
  107. 107. “Only the children know what they are looking for.” The Little Prince 106
  108. 108. Thank you 107
  109. 109. Q&A 108