How to Build Awesome Android Libraries (360 AnDev 2021)

This talk is a collection of advice about building Android libraries or SDKs, highlighting some of the less obvious things you can do to make your library great.

Many of the recommendations will also make your life easier in any multi-module project, even if you're not publishing libraries anywhere.

All of this is based on my own open-source library development work - which I do both in my free time and at my day job working on the Stream Chat Android SDK.

More info and resources: https://zsmb.co/appearances/360-andev-2021/

Transcript

1. zsmb.co zsmb13 How to Build Awesome Android Libraries Márton Braun
2. Introduction
3. Introduction RainbowCake rainbowcake/rainbowcake Krate AutSoft/Krate MaterialDrawerKt zsmb13/MaterialDrawerKt requireKTX zsmb13/requireKTX
4. GetStream/stream-chat-android › Open source chat SDK
5. GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events
6. GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events
7. GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events › Offline support › Pre-built UI components
8. GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events › Offline support › Pre-built UI components
9. GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events › Offline support › Pre-built UI components › Kotlin-first APIs
10. GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events › Offline support › Pre-built UI components › Kotlin-first APIs › Free for makers!
11. GetStream/stream-chat-android
12. TL;DW Minimize ALL the things!
13. TL;DW Minimize ALL the things! › Features of the library
14. TL;DW Minimize ALL the things! › Features of the library › Public API
15. TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies
16. TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies › Performance impact
17. TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies › Performance impact › Enabled features by default
18. TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies › Performance impact › Enabled features by default › Requirements
19. Public API
20. Public API › Minimal API
21. Public API › Minimal API Item 15: Minimize the accessibility of classes and members
22. Public API › Minimal API › Deprecations
23. Public API › Minimal API › Deprecations
24. Public API › Minimal API › Deprecations › Easy to use
25. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse
26. Public API zsmb.co/talks/mastering-api-visibility/ › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility
27. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating
28. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating
29. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating › Dependencies interface ChatClient { suspend fun sendMessage(message: Message): Message }
30. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating › Dependencies public interface Call<T> { public fun execute(): Result<T> public fun enqueue(callback: Callback<T>) } public suspend fun <T> Call<T>.await(): Result<T>
31. Dependencies
32. Dependencies › Minimal dependencies
33. Dependencies › Minimal dependencies › Size
34. Dependencies › Minimal dependencies › Size › Many libraries per app
35. Dependencies › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps
36. Dependencies › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps › Complexity
37. Dependencies › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps › Complexity › Version conflicts
38. Dependencies Library 2 Library 1 Appcompat 1.4 alpha Appcompat 1.2 App › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps › Complexity › Version conflicts
39. Version updates
40. Version updates
41. implementation vs api Library 1 App
42. implementation vs api Library 1 Library 2 App implementation
43. implementation vs api Library 1 Library 2 App implementation
44. implementation vs api Library 1 Library 2 App api Library 1 Library 2 App implementation
45. library.aar
46. library.aar resources layout.xml values.xml
47. library.aar resources layout.xml values.xml AndroidManifest.xml
48. library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar
49. library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt
50. library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt library- sources.jar library- javadoc.jar *.kt *.html
51. The POM file library.pom <?xml version="1.0" encoding="UTF-8"?> <project> <groupId>io.getstream</groupId> <artifactId>stream-chat-android-client</artifactId> <version>4.12.0</version> <packaging>aar</packaging> <name>stream-chat-android-client</name> <dependencies> <dependency> <groupId>org.jetbrains.kotlin</groupId> <artifactId>kotlin-stdlib</artifactId> <version>1.5.10</version> <scope>runtime</scope> </dependency> ... </dependencies> </project> library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt library- sources.jar library- javadoc.jar *.kt *.html
52. The POM file library.pom <?xml version="1.0" encoding="UTF-8"?> <project> <groupId>io.getstream</groupId> <artifactId>stream-chat-android-client</artifactId> <version>4.12.0</version> <packaging>aar</packaging> <name>stream-chat-android-client</name> <dependencies> <dependency> <groupId>org.jetbrains.kotlin</groupId> <artifactId>kotlin-stdlib</artifactId> <version>1.5.10</version> <scope>runtime</scope> </dependency> ... </dependencies> </project>
53. The POM file library.pom <?xml version="1.0" encoding="UTF-8"?> <project> <groupId>io.getstream</groupId> <artifactId>stream-chat-android-client</artifactId> <version>4.12.0</version> <packaging>aar</packaging> <name>stream-chat-android-client</name> <dependencies> <dependency> <groupId>org.jetbrains.kotlin</groupId> <artifactId>kotlin-stdlib</artifactId> <version>1.5.10</version> <scope>runtime</scope> </dependency> ... </dependencies> </project>
54. The POM file library.pom <?xml version="1.0" encoding="UTF-8"?> <project> <groupId>io.getstream</groupId> <artifactId>stream-chat-android-client</artifactId> <version>4.12.0</version> <packaging>aar</packaging> <name>stream-chat-android-client</name> <dependencies> <dependency> <groupId>org.jetbrains.kotlin</groupId> <artifactId>kotlin-stdlib</artifactId> <version>1.5.10</version> <scope>runtime</scope> </dependency> ... </dependencies> </project>
55. Repositories MavenCentral Library 1
56. Repositories MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
57. Repositories MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
58. Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
59. Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
60. Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
61. Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
62. Multi-module libraries my-awesome-lib
63. Multi-module libraries my-awesome-lib
64. Multi-module libraries my-awesome-lib my-awesome-lib-plus my-awesome-lib-core
65. Multi-module libraries my-awesome-lib-plus my-awesome-lib-core my-awesome-lib
66. rx Multi-module libraries my-awesome-lib-plus my-awesome-lib-core
67. Multi-module libraries plus rxjava my-awesome-lib-rx my-awesome-lib-core
68. Fat AARs ui-components core offline client
69. Fat AARs ui-components core offline client App
70. Fat AARs ui-components core offline client App
71. Fat AARs ui-components core offline client App
72. Fat AARs
73. Fat AARs
74. Fat AARs
75. Fat AARs "At the moment we are talking with Gradle about being able to merge dependencies from multiple projects (that are being bundled), as that part is a problem in the JVM ecosystem as well. Once that is in, we can focus on the Android-specific features (Android resources, manifest etc.)." 2020-12-02
76. Fat AARs fat-aar-plugin vigidroid/fat-aar-plugin fataar-gradle-plugin Mobbeel/fataar-gradle-plugin fat-aar-android kezong/fat-aar-android android-fat-aar adwiv/android-fat-aar
77. Startup impact
78. Startup impact › Don’t hog startup › Competing with other libraries
79. Startup impact › Don’t hog startup › Competing with other libraries › Initialize on-demand
80. Startup impact › Don’t hog startup › Competing with other libraries › Initialize on-demand › App Startup
81. Logging
82. Logging › Don’t log by default
83. Logging › Don’t log by default val client = ChatClient.Builder("apiKey", context) .logLevel(ChatLogLevel.ALL) .build()
84. Logging › Don’t log by default › Don’t enable any feature by default val client = ChatClient.Builder("apiKey", context) .logLevel(ChatLogLevel.ALL) .build()
85. Requirements › Minimal requirements › Make integrating your library easy › Don’t force things on your clients
86. API level App Library 1 Library 2 Library 3 API 21 API 21 API 19 API 15
87. API level App Library 1 Library 2 Library 3 API 21 API 21 API 19 API 15
88. API level App Library 1 Library 2 Library 3 API 21 API 21 API 23 API 15
89. API level App Library 1 Library 2 Library 3 API 23 API 21 API 23 API 15
90. Permissions & features library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt
91. Permissions & features <?xml version="1.0" encoding="utf-8"?> <manifest> <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="29" /> <uses-feature android:name="android.hardware.bluetooth" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <uses-permission android:name="android.permission.CAMERA" /> <application> <provider /> <activity /> <activity /> </application> </manifest> library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt
92. Permissions & features <?xml version="1.0" encoding="utf-8"?> <manifest> <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="29" /> <uses-feature android:name="android.hardware.bluetooth" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <uses-permission android:name="android.permission.CAMERA" /> <application> <provider /> <activity /> <activity /> </application> </manifest> AndroidManifest.xml
93. <?xml version="1.0" encoding="utf-8"?> <manifest> <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="29" /> <uses-feature android:name="android.hardware.bluetooth" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <uses-permission android:name="android.permission.CAMERA" /> <application> <provider /> <activity /> <activity /> </application> </manifest> Permissions & features AndroidManifest.xml
94. <?xml version="1.0" encoding="utf-8"?> <manifest> <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="29" /> <uses-feature android:name="android.hardware.bluetooth" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <uses-permission android:name="android.permission.CAMERA" /> <application> <provider /> <activity /> <activity /> </application> </manifest> Permissions & features AndroidManifest.xml
95. <?xml version="1.0" encoding="utf-8"?> <manifest> <uses-sdk android:minSdkVersion="21" android:targetSdkVersion="29" /> <uses-feature android:name="android.hardware.bluetooth" /> <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /> <uses-permission android:name="android.permission.CAMERA" /> <application> <provider /> <activity /> <activity /> </application> </manifest> Permissions & features AndroidManifest.xml
96. Resource prefixes android { resourcePrefix 'stream_ui_' }
97. Resource prefixes <?xml version="1.0" encoding="utf-8"?> <resources> <color name="stream_ui_accent_blue">#005FFF</color> <color name="stream_ui_accent_red">#FF3742</color> <color name="stream_ui_ ">#20E070</color> </resources> accent_green android { resourcePrefix 'stream_ui_' }
98. Resource prefixes android { resourcePrefix 'stream_ui_' } <?xml version="1.0" encoding="utf-8"?> <resources> <color name="stream_ui_accent_blue">#005FFF</color> <color name="stream_ui_accent_red">#FF3742</color> <color name=" ">#20E070</color> </resources> accent_green
99. Resource prefixes android { resourcePrefix 'stream_ui_' } <?xml version="1.0" encoding="utf-8"?> <resources> <color name="stream_ui_accent_blue">#005FFF</color> <color name="stream_ui_accent_red">#FF3742</color> <color name=" ">#20E070</color> </resources> accent_green Resource named 'accent_green' does not start with the project's resource prefix 'stream_ui_'; rename to 'stream_ui_accent_green' ?
100. Resource prefixes android { resourcePrefix 'stream_ui_' } <?xml version="1.0" encoding="utf-8"?> <resources> <declare-styleable name="MessageInputView"> <attr name="streamUiAttachButtonEnabled" format="boolean" /> <attr name="streamUiAttachButtonIcon" format="reference" /> <attr name="streamUiMentionsEnabled" format="boolean" /> <attr name="streamUiMentionsIcon" format="reference" /> <attr name="streamUiAttachmentMaxFileSizeMb" format="integer" /> </declare-styleable> </resources>
101. Resource prefixes android { resourcePrefix 'stream_ui_' }
102. Private resources
103. Private resources <?xml version="1.0" encoding="utf-8"?> <resources> <public name="mylib_app_name" type="string" /> <public name="mylib_public_string" type="string" /> </resources>
104. Explicitly public resources <?xml version="1.0" encoding="utf-8"?> <resources> <public name="mylib_app_name" type="string" /> <public name="mylib_public_string" type="string" /> </resources>
105. Proguard library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt
106. Proguard ## Stream Chat Android Client Proguard Rules -keep class io.getstream.chat.android.client.api.* { *; } -keep class io.getstream.chat.android.client.api.models.* { *; } -keep class io.getstream.chat.android.client.api2.model.** { *; } -keep class io.getstream.chat.android.client.errors.* { *; } -keep class io.getstream.chat.android.client.events.* { *; } -keep class io.getstream.chat.android.client.models.* { *; } -keep class io.getstream.chat.android.client.parser.* { *; } -keep class io.getstream.chat.android.client.socket.* { *; } -keep class io.getstream.chat.android.client.utils.Result { *; } -keep class io.getstream.chat.android.client.utils.SyncStatus { *; } library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt proguard.txt
107. Proguard ## Stream Chat Android Client Proguard Rules -keep class io.getstream.chat.android.client.api.* { *; } -keep class io.getstream.chat.android.client.api.models.* { *; } -keep class io.getstream.chat.android.client.api2.model.** { *; } -keep class io.getstream.chat.android.client.errors.* { *; } -keep class io.getstream.chat.android.client.events.* { *; } -keep class io.getstream.chat.android.client.models.* { *; } -keep class io.getstream.chat.android.client.parser.* { *; } -keep class io.getstream.chat.android.client.socket.* { *; } -keep class io.getstream.chat.android.client.utils.Result { *; } -keep class io.getstream.chat.android.client.utils.SyncStatus { *; } proguard.txt
108. Proguard ## Stream Chat Android Client Proguard Rules -keep class io.getstream.chat.android.client.api.* { *; } -keep class io.getstream.chat.android.client.api.models.* { *; } -keep class io.getstream.chat.android.client.api2.model.** { *; } -keep class io.getstream.chat.android.client.errors.* { *; } -keep class io.getstream.chat.android.client.events.* { *; } -keep class io.getstream.chat.android.client.models.* { *; } -keep class io.getstream.chat.android.client.parser.* { *; } -keep class io.getstream.chat.android.client.socket.* { *; } -keep class io.getstream.chat.android.client.utils.Result { *; } -keep class io.getstream.chat.android.client.utils.SyncStatus { *; } -dontoptimize -dontshrink proguard.txt
109. Proguard android { buildTypes { release { proguardFiles getDefaultProguardFile('proguard-android-optimize.txt’), 'proguard-rules.pro' consumerProguardFiles 'consumer-proguard-rules.pro' } debug { consumerProguardFiles 'consumer-proguard-rules.pro' } } }
110. Proguard android { buildTypes { release { proguardFiles getDefaultProguardFile('proguard-android-optimize.txt’), 'proguard-rules.pro' consumerProguardFiles 'consumer-proguard-rules.pro' } debug { consumerProguardFiles 'consumer-proguard-rules.pro' } } }
111. Proguard android { buildTypes { release { proguardFiles getDefaultProguardFile('proguard-android-optimize.txt’), 'proguard-rules.pro' consumerProguardFiles 'consumer-proguard-rules.pro' } debug { consumerProguardFiles 'consumer-proguard-rules.pro' } } }
112. Testing
113. Testing › Lots of responsibility
114. Testing › Lots of responsibility › Diverse environments
115. Testing › Lots of responsibility › Diverse environments › Can’t assume anything
116. Testing › Lots of responsibility › Diverse environments › Can’t assume anything › Devices, architectures, OS versions, stores
117. Testing › Lots of responsibility › Diverse environments › Can’t assume anything › Devices, architectures, OS versions, stores › Other frameworks and libraries
118. Testing › Lots of responsibility › Diverse environments › Can’t assume anything › Devices, architectures, OS versions, stores › Other frameworks and libraries › Your code is not final
119. Documentation
120. Documentation › Have documentation
121. Documentation › Have documentation › README
122. Documentation › Have documentation › README › What it does
123. Documentation › Have documentation › README › What it does › Setup instructions
124. Documentation › Have documentation › README › What it does › Setup instructions › Screenshots
125. Documentation › Have documentation › README › Code comments
126. Documentation › Have documentation › README › Code comments
127. Documentation › Have documentation › README › Code comments
128. Documentation › Have documentation › README › Code comments › Sample app
129. Documentation › Have documentation › README › Code comments › Sample app › Update strategy
130. Publishing
131. Publishing › Maven repositories
132. Publishing › Maven repositories › Main options
133. Publishing › Maven repositories › Main options › Jcenter
134. Publishing › Maven repositories › Main options › Jcenter
135. Publishing › Maven repositories › Main options › Jcenter
136. Publishing › Maven repositories › Main options › Jcenter
137. Publishing › Maven repositories › Main options › Jcenter › Jitpack
138. Publishing › Maven repositories › Main options › Jcenter › Jitpack
139. Publishing › Maven repositories › Main options › Jcenter › Jitpack › Maven Central
140. Publishing › Maven repositories › Main options › Jcenter › Jitpack › Maven Central
141. Publishing › Coordinates
142. Publishing › Coordinates io.getstream:stream-chat-android-client:4.12.0
143. Publishing › Coordinates io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID
144. Publishing Group ID io.getstream : stream-chat-android-client : 4.12.0 Version Artifact ID › Coordinates
145. Publishing › Coordinates io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID
146. Publishing › Coordinates › Versioning io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID
147. Publishing › Coordinates › Versioning semver.org io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID
148. Publishing › Coordinates › Versioning › License
149. Publishing › Coordinates › Versioning › License tldrlegal.com
150. Release checklist
151. Community
152. Community › Open source vs source available
153. Community › Open source vs source available › Address issues and discussions
154. Community › Open source vs source available › Address issues and discussions › Take PR contributions
155. Community › Open source vs source available › Address issues and discussions › Take PR contributions › Be open for feedback*
156. Community › Open source vs source available › Address issues and discussions › Take PR contributions › Be open for feedback* “You're supposed to side with the community, but you should also have a say in what you're building” – Filip Babić
157. Resources • Nishant Srivastava’s excellent talks  Things I wish I knew when I started building Android SDK/Libraries  https://www.youtube.com/watch?v=G-x9wRWwICo  Things I wish I knew when I started building Android Libraries Vol 2  https://www.youtube.com/watch?v=jQyt3HSmx2I • Mastering API Visibility in Kotlin  https://zsmb.co/talks/mastering-api-visibility/  Kotlin/binary-compatibility-validator  https://github.com/Kotlin/binary-compatibility-validator • Publishing Android libraries to MavenCentral in 2021  https://proandroiddev.com/publishing-android-libraries-to-mavencentral-in-2021-8ac9975c3e52
158. Resources • Jeroen Mols’ library development articles  https://jeroenmols.com/blog/2020/10/28/library-gettingstarted/  What is a library and how is it deployed  https://jeroenmols.com/blog/2020/11/04/library-modularization/  Publishing submodules, fat AARs, controlling access  https://jeroenmols.com/blog/2020/11/11/library-dependencies/  Dependency conflicts and version incompatibilities • More on fat AARs  Sam Edwards’ article  https://handstandsam.com/2018/07/13/why-we-need-fat-aars-for-android-libraries/  Open issue on Google’s issue tracker  https://issuetracker.google.com/issues/62121508
159. zsmb13 zsmb.co/talks
160. How to Build Awesome Android Libraries zsmb.co/talks zsmb13 Márton Braun › Minimize all the things! › Public API › Dependencies › Size and impact › Publishing and releases › Don’t forget the docs!