[Devoxx Belgium '18] Things I wish I knew when I started building Android Libraries/SDK -Vol.2

Building an Android library in the current times is way different than what it used to be earlier. Things have changed considerably and keeping up to date with them is a now a necessity than just some acquirable knowledge.

This session in a second part to the last year’s talk at Droidcon Berlin 2017 with the same title. In this session we will dive deeper into best practices and ways of architecting android libraries. You will get to learn about the common pitfalls and how to overcome them by using the right approach such as leveraging architecture components and making your android libraries lifecycle aware. We will also be covering how one can leverage Kotlin language when developing android libraries as well as information around API design and exploring the path to becoming a better Android Library Developer.

By the end of this session, you will be all set to build android libraries that scale and have API which contributes to developer happiness.

Google Slides: https://docs.google.com/presentation/d/1svOPXO9dYeuim1uHHymciIobdFKMb-4TKNUrvWmovH8/edit?usp=sharing

Video: https://www.youtube.com/watch?v=jQyt3HSmx2I

2. OSS Android libraries developed
3. Android ARchive(AAR) @nisrulz
4. AAR = Java ARchive(JAR) + Resources @nisrulz
5. AAR = Java ARchive(JAR) + Resources @nisrulz Sensey: https://github.com/nisrulz/sensey
6. AAR = Java ARchive(JAR) + Resources @nisrulz
7. Using an AAR as dependency @nisrulz
8. Using an AAR as dependency @nisrulz repositories{ flatDir{ dirs 'libs' } } dependencies { implementation(name:'nameOfYourAARFileWithoutExtension', ext:'aar') }
9. Using an AAR as dependency @nisrulz repositories{ flatDir{ dirs 'libs' } } dependencies { implementation(name:'nameOfYourAARFileWithoutExtension', ext:'aar') } // None of the dependencies of the library are downloaded
10. Why doesn’t my AAR download transitive dependencies? @nisrulz
11. Sensey’s build.gradle @nisrulz dependencies { ... // Other testing dependencies // Transitive dependency: Support Compat library implementation "com.android.support:support-compat:27.0.2" }
12. Sensey’s AAR @nisrulz
13. Sensey’s AAR @nisrulz No build.gradle file
14. Maven Artifact @nisrulz
15. @nisrulz Maven Artifact
16. POM? @nisrulz
17. POM @nisrulz + Stands for Project Object Model + Is a XML file + Contains + Information about the project + Configuration details used by Maven to build the project
18. POM @nisrulz POM of Sensey Android Library <?xml version="1.0" encoding="UTF-8"?> <project xsi:schemaLocation="..." xmlns="..."xmlns:xsi="..."> <modelVersion>4.0.0</modelVersion> <groupId>com.github.nisrulz</groupId><artifactId>sensey</artifactId><version>1.8.0</version> <packaging>aar</packaging><name>sensey</name> <description>Android library which makes playing with sensor events &amp; detecting gestures a breeze.</description> <url>https://github.com/nisrulz/sensey</url> <licenses> <license> <name>The Apache Software License, Version 2.0</name><url>http://www.apache.org/licenses/LICENSE-2.0.txt</url> </license> </licenses> <developers> <developer><id>nisrulz</id><name>Nishant Srivastava</name><email>nisrulz@gmail.com</email></developer> </developers> <scm> <connection>https://github.com/nisrulz/sensey.git</connection> <developerConnection>https://github.com/nisrulz/sensey.git</developerConnection> <url>https://github.com/nisrulz/sensey</url> </scm> <dependencies> <dependency> <groupId>com.android.support</groupId> <artifactId>support-compat</artifactId><version>27.0.2</version> <scope>runtime</scope> </dependency> <dependency> ... </dependency> </dependencies> </project>
19. POM @nisrulz POM of Sensey Android Library <?xml version="1.0" encoding="UTF-8"?> <project xsi:schemaLocation="..." xmlns="..."xmlns:xsi="..."> <modelVersion>4.0.0</modelVersion> <groupId>com.github.nisrulz</groupId><artifactId>sensey</artifactId><version>1.8.0</version> <packaging>aar</packaging><name>sensey</name> <description>Android library which makes playing with sensor events &amp; detecting gestures a breeze.</description> <url>https://github.com/nisrulz/sensey</url> <licenses> <license> <name>The Apache Software License, Version 2.0</name><url>http://www.apache.org/licenses/LICENSE-2.0.txt</url> </license> </licenses> <developers> <developer><id>nisrulz</id><name>Nishant Srivastava</name><email>nisrulz@gmail.com</email></developer> </developers> <scm> <connection>https://github.com/nisrulz/sensey.git</connection> <developerConnection>https://github.com/nisrulz/sensey.git</developerConnection> <url>https://github.com/nisrulz/sensey</url> </scm> <dependencies> <dependency> <groupId>com.android.support</groupId> <artifactId>support-compat</artifactId><version>27.0.2</version> <scope>runtime</scope> </dependency> <dependency> ... </dependency> </dependencies> </project>
20. POM @nisrulz POM of Sensey Android Library <?xml version="1.0" encoding="UTF-8"?> <project xsi:schemaLocation="..." xmlns="..."xmlns:xsi="..."> ... <dependencies> <dependency> <groupId>com.android.support</groupId> <artifactId>support-compat</artifactId><version>27.0.2</version> <scope>runtime</scope> </dependency> <dependency> ... </dependency> </dependencies> </project>
21. Bundled Proguard Configs @nisrulz
22. Bundled Proguard Configs @nisrulz android { release { minifyEnabled true // Rules to be used during the AAR generation proguardFiles 'proguard-rules-for-building-library.pro' // Rules appended to the integrating app consumerProguardFiles 'proguard-rules-for-using-library.pro' } ... }
23. Bundled Proguard Configs @nisrulz Fuel: https://github.com/kittinunf/Fuel
24. Bundled Proguard Configs @nisrulz
25. Bundled Proguard Configs @nisrulz # Fuel’s bundled Proguard file # Without specifically keeping this class, # callbacks on android don't function properly. -keep class com.github.kittinunf.fuel.android.util.AndroidEnvironment
26. Bundled Proguard Configs @nisrulz # To check the merged configuration # Add the below to your current config -printconfiguration proguard-merged-config.txt
27. Bundled Proguard Configs @nisrulz # DON'T DO THIS -dontobfuscate -optimizations !code/allocation/variable # Effectively no optimizations -keep public class * { public protected *; }
28. Bundled Proguard Configs @nisrulz # DON'T DO THIS # Adding the below in library proguard rules disables # the optimizations in the Android app -dontoptimze
29. Modularization @nisrulz
30. Modularization @nisrulz
31. Modularization @nisrulz EasyDeviceInfo: https://github.com/nisrulz/easydeviceinfo
32. Modularization @nisrulz dependencies { def libVer = {latest_version} // Base + Ads Bundled Library implementation "com.github.nisrulz:easydeviceinfo:$libVer" // Base Library implementation "com.github.nisrulz:easydeviceinfo-base:$libVer" // Ads Library implementation "com.github.nisrulz:easydeviceinfo-ads:$libVer" }
33. Modularization @nisrulz <!-- POM file for com.github.nisrulz:easydeviceinfo --> <project xsi:schemaLocation="..." xmlns="..." xmlns:xsi="..."> ... <dependencies> <dependency> <groupId>com.github.nisrulz</groupId> <artifactId>easydeviceinfo-ads</artifactId> <version>2.4.1</version> <scope>compile</scope> </dependency> <dependency> <groupId>com.github.nisrulz</groupId> <artifactId>easydeviceinfo-base</artifactId> <version>2.4.1</version> <scope>compile</scope> </dependency> ... </dependencies> </project>
34. Modularization @nisrulz <!-- POM file for com.github.nisrulz:easydeviceinfo--> <project xsi:schemaLocation="..." xmlns="..." xmlns:xsi="..."> ... <dependencies> <dependency> <groupId>com.github.nisrulz</groupId> <artifactId>easydeviceinfo-ads</artifactId> <version>2.4.1</version> <scope>compile</scope> </dependency> <dependency> <groupId>com.github.nisrulz</groupId> <artifactId>easydeviceinfo-base</artifactId> <version>2.4.1</version> <scope>compile</scope> </dependency> ... </dependencies> </project>
35. Modularization @nisrulz <!-- POM file for com.github.nisrulz:easydeviceinfo--> <project xsi:schemaLocation="..." xmlns="..." xmlns:xsi="..."> ... <dependencies> <dependency> <groupId>com.github.nisrulz</groupId> <artifactId>easydeviceinfo-ads</artifactId> <version>2.4.1</version> <scope>compile</scope> </dependency> <dependency> <groupId>com.github.nisrulz</groupId> <artifactId>easydeviceinfo-base</artifactId> <version>2.4.1</version> <scope>compile</scope> </dependency> ... </dependencies> </project>
36. Modularization @nisrulz <!-- POM file for com.github.nisrulz:easydeviceinfo-ads --> <project xsi:schemaLocation="..." xmlns="..." xmlns:xsi="..."> ... <dependencies> <dependency> <groupId>com.github.nisrulz</groupId> <artifactId>easydeviceinfo-common</artifactId><version>2.4.1</version> <scope>compile</scope> </dependency> <dependency> <groupId>com.google.android.gms</groupId> <artifactId>play-services-basement</artifactId><version>11.8.0</version> <scope>runtime</scope> </dependency> ... </dependencies> </project>
37. Modularization @nisrulz <!-- POM file for com.github.nisrulz:easydeviceinfo-ads --> <project xsi:schemaLocation="..." xmlns="..." xmlns:xsi="..."> ... <dependencies> <dependency> <groupId>com.github.nisrulz</groupId> <artifactId>easydeviceinfo-common</artifactId><version>2.4.1</version> <scope>compile</scope> </dependency> <dependency> <groupId>com.google.android.gms</groupId> <artifactId>play-services-basement</artifactId><version>11.8.0</version> <scope>runtime</scope> </dependency> ... </dependencies> </project>
38. Avoiding Resource Name Conflicts @nisrulz
39. @nisrulz Conflict occurs between a library & app resource > Project will not compile What happens when..
40. @nisrulz Conflict occurs between 2 libraries integrated in the app > Resources from library defined first in build.gradle gets included What happens when..
41. @nisrulz Add a prefix to all your resources. Solution?
42. @nisrulz Add a prefix to all your resources. Enforce this in Android Studio android { resourcePrefix 'YOUR_PREFIX_' // i.e 'sensey_' } Solution?
43. @nisrulz Solution? Resource named ‘app_name’ does not start with the project’s resource prefix ‘sensey_’; Rename to `sensey_app_name`?
44. minSdkVersion Restriction @nisrulz
45. @nisrulz minSdkVersion of app >= minSdkVersion of library minSdk Restriction
46. @nisrulz minSdk Restriction
47. @nisrulz Manifest merger failed : uses-sdk:minSdkVersion 14 cannot be smaller than version 21 declared in library [:sensey] Suggestion: + Use a compatible library with a minSdk of at most 14 + Increase this project's minSdk version to at least 21 + Use tools:overrideLibrary="com.github.nisrulz.sensey" to force usage (may lead to runtime failures) minSdk Restriction
48. @nisrulz Manifest merger failed : uses-sdk:minSdkVersion 14 cannot be smaller than version 21 declared in library [:sensey] Suggestion: + Use a compatible library with a minSdk of at most 14 + Increase this project's minSdk version to at least 21 + Use tools:overrideLibrary="com.github.nisrulz.sensey" to force usage (may lead to runtime failures) minSdk Restriction
49. @nisrulz Manifest merger failed : uses-sdk:minSdkVersion 14 cannot be smaller than version 21 declared in library [:sensey] Suggestion: + Use a compatible library with a minSdk of at most 14 + Increase this project's minSdk version to at least 21 + Use tools:overrideLibrary="com.github.nisrulz.sensey" to force usage (may lead to runtime failures) minSdk Restriction
50. @nisrulz <manifest xmlns:android="..." xmlns:tools="http://schemas.android.com/tools" package="com.github.nisrulz.senseysample"> <uses-sdk tools:overrideLibrary="com.github.nisrulz.sensey"/> <application ...> ... </application> </manifest> minSdk Restriction
51. @nisrulz <manifest xmlns:android="..." xmlns:tools="http://schemas.android.com/tools" package="com.github.nisrulz.senseysample"> <uses-sdk tools:overrideLibrary="com.github.nisrulz.sensey"/> <application ...> ... </application> </manifest> minSdk Restriction
52. Access Visibility vs Code Organization @nisrulz
53. Visibility vs Organization @nisrulz + Code organized in individual packages; everything is public
54. Visibility vs Organization @nisrulz + Code organized in individual packages; everything is public + Code organized inside one package; everything is package private and only public on demand
55. Visibility vs Organization @nisrulz + Code organized in individual packages; everything is public + Code organized inside one package; everything is package private and only public on demand But if in Kotlin land, + Code organized in individual packages; everything is internal and only public on demand
56. Visibility vs Organization @nisrulz // file name: exampleLibrary.kt // module name: example package com.example.library
57. Visibility vs Organization @nisrulz // file name: exampleLibrary.kt // module name: example package com.example.library // visible inside exampleLibrary.kt private fun setup() { ... }
58. Visibility vs Organization @nisrulz // file name: exampleLibrary.kt // module name: example package com.example.library // visible inside exampleLibrary.kt private fun setup() { ... } // property is visible everywhere public var name: String = "ExampleLib" // setter is visible only in exampleLibrary.kt private set{...}
59. Visibility vs Organization @nisrulz // file name: exampleLibrary.kt // module name: example package com.example.library // visible inside exampleLibrary.kt private fun setup() { ... } // property is visible everywhere public var name: String = "ExampleLib" // setter is visible only in exampleLibrary.kt private set{...} // visible inside the module i.e example internal val debugTag = "Example-Debug"
60. Lifecycle-Aware Android Library @nisrulz
61. Lifecycle Components @nisrulz Classes designed to help deal with Android lifecycle + Lifecycle + LifecycleOwner + LifecycleObserver
62. Lifecycle Components @nisrulz Classes designed to help deal with Android lifecycle
63. Lifecycle Components @nisrulz Classes designed to help deal with Android lifecycle i.e Activity, Fragment, Service, Custom
64. LifecycleObserver @nisrulz dependencies { def lifecycleVer = "1.1.1" // Runtime implementation "android.arch.lifecycle:runtime:$lifecycleVer" // Annotation Support annotationProcessor "android.arch.lifecycle:compiler:$lifecycleVer" ... }
65. LifecycleObserver @nisrulz object AwesomeLibrary : LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_CREATE) fun init() { ... } @OnLifecycleEvent(Lifecycle.Event.ON_START) fun onStart() { ... } ... @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY) fun cleanup() { ...} }
66. LifecycleOwner @nisrulz class MainActivity : AppCompatActivity() { // LifecycleOwner override fun onResume() { // Add lifecycle observer lifecycle.addObserver(AwesomeLibrary.INSTANCE) } override fun onStop() { // Remove lifecycle observer lifecycle.removeObserver(AwesomeLibrary.INSTANCE) } }
67. ProcessLifecycleOwner @nisrulz Class that tracks the lifecycle of whole application process
68. ProcessLifecycleOwner @nisrulz dependencies { def lifecycleVer = "1.1.1" // For ProcessLifecycleOwner implementation "android.arch.lifecycle:extensions:$lifecycleVer" ... }
69. ProcessLifecycleOwner @nisrulz extension artifact automatically adds <provider> element to your manifest
70. ProcessLifecycleOwner @nisrulz <manifest > <application> ... <provider android:name="android.arch.lifecycle.ProcessLifecycleOwnerInitializer" android:authorities="com.example.app.lifecycle-trojan" android:exported="false" android:multiprocess="true" /> </application> </manifest>
71. ProcessLifecycleOwner @nisrulz // Source code // Internal class to initialize Lifecycles. public class ProcessLifecycleOwnerInitializer extends ContentProvider { @Override public boolean onCreate() { ... ProcessLifecycleOwner.init(getContext()); return true; } ... }
72. ProcessLifecycleOwner @nisrulz Initializes ProcessLifecycleOwner even if your app does not use it! Why? To invoke ProcessLifecycleOwner as soon as process starts
73. Auto Initialize Android Library @nisrulz
74. AutoInit Android Library @nisrulz Android Libraries need Android context to handle simple tasks such as + Hook into Android Runtime + Access app resources + Use System Services + Register BroadcastReceiver
75. AutoInit Android Library @nisrulz public class MyApplication extends Application { @Override public void onCreate() { super.onCreate(); // Init android library MyAwesomeLibrary.init(this); } }
76. AutoInit Android Library @nisrulz public class MyApplication extends Application { @Override public void onCreate() { super.onCreate(); // Init android library MyAwesomeLibrary.init(this); } }
77. AutoInit Android Library @nisrulz public class MyApplication extends Application { @Override public void onCreate() { super.onCreate(); // Init android library MyAwesomeLibrary.init(this); } }
78. AutoInit Android Library @nisrulz <application android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:name=".MyApplication" ... >
79. AutoInit Android Library @nisrulz ContentProvider “can be” used to simplify the process. How? ContentProvider is + Created and initialized (on the main thread) before all other components + Participate in manifest merging at build time.
80. AutoInit Android Library @nisrulz public class AwesomeLibInitProvider extends ContentProvider { ... @Override public boolean onCreate() { // get the context (Application context) Context context = getContext(); // initialize AwesomeLib here AwesomeLib.getInstance().init(context); return false; } ... }
81. AutoInit Android Library @nisrulz public class AwesomeLibInitProvider extends ContentProvider { ... @Override public boolean onCreate() { // get the context (Application context) Context context = getContext(); // initialize AwesomeLib here AwesomeLib.getInstance().init(context); return false; } ... }
82. AutoInit Android Library @nisrulz <manifest xmlns:android=".." package="github.nisrulz.sample.awesomelib"> <application> <provider android:name=".AwesomeLibInitProvider" android:authorities="${applicationId}.awesomelibinitprovider" android:enabled="true" android:exported="false"></provider> </application> </manifest>
83. AutoInit Android Library @nisrulz <manifest xmlns:android=".." package="github.nisrulz.sample.awesomelib"> <application> <provider android:name=".AwesomeLibInitProvider" android:authorities="${applicationId}.awesomelibinitprovider" android:enabled="true" android:exported="false"></provider> </application> </manifest>
84. AutoInit Android Library @nisrulz <manifest xmlns:android=".." package="github.nisrulz.sample.awesomelib"> <application> <provider android:name=".AwesomeLibInitProvider" android:authorities="${applicationId}.awesomelibinitprovider" android:enabled="true" android:exported="false"></provider> </application> </manifest>
85. AutoInit Android Library @nisrulz <manifest xmlns:android=".." package="github.nisrulz.sample.awesomelib"> <application> <provider android:name=".AwesomeLibInitProvider" android:authorities="${applicationId}.awesomelibinitprovider" android:enabled="true" android:exported="false"></provider> </application> </manifest>
86. AutoInit Android Library @nisrulz ContentProvider “can be” used to simplify the process. Why it shouldn’t be + There can be only one Content Provider with a given “authority” string + Only run on main thread; does not support multi process
87. Links/References @nisrulz Android Libraries I have built: https://github.com/nisrulz/nisrulz.github.io#open-source-co ntributions Auto initialize android library example: https://github.com/nisrulz/android-examples/tree/develop/Au toInitLibrary Lifecycle Aware android library example: https://github.com/nisrulz/android-examples/tree/develop/Li feCycleCompForLib
88. twitter.com/nisrulz github.com/nisrulz www.nisrulz.com
89. twitter.com/nisrulz github.com/nisrulz www.nisrulz.com