How to Build Awesome Android Libraries (Droidcon Webinar)

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/droidcon-webinar-june-2021/

Transcript

1. zsmb.co zsmb13 How to Build Awesome Android Libraries Márton Braun
2. Introduction
3. Introduction MaterialDrawerKt zsmb13/MaterialDrawerKt
4. Introduction RainbowCake rainbowcake/rainbowcake MaterialDrawerKt zsmb13/MaterialDrawerKt
5. Introduction RainbowCake rainbowcake/rainbowcake Krate AutSoft/Krate MaterialDrawerKt zsmb13/MaterialDrawerKt
6. Introduction RainbowCake rainbowcake/rainbowcake Krate AutSoft/Krate MaterialDrawerKt zsmb13/MaterialDrawerKt requireKTX zsmb13/requireKTX
7. GetStream/stream-chat-android › Open source chat SDK
8. GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events
9. GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events
10. GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events › Offline support › Pre-built UI components
11. GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events › Offline support › Pre-built UI components
12. GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events › Offline support › Pre-built UI components › Kotlin-first APIs
13. 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!
14. GetStream/stream-chat-android
15. TL;DW Minimize ALL the things!
16. TL;DW Minimize ALL the things! › Features of the library
17. TL;DW Minimize ALL the things! › Features of the library › Public API
18. TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies
19. TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies › Performance impact
20. TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies › Performance impact › Enabled features by default
21. TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies › Performance impact › Enabled features by default › Requirements
22. Public API
23. Public API › Minimal API
24. Public API › Minimal API Item 15: Minimize the accessibility of classes and members
25. Public API › Minimal API › Deprecations
26. Public API › Minimal API › Deprecations
27. Public API › Minimal API › Deprecations › Easy to use
28. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse
29. Public API zsmb.co/talks/mastering-api-visibility/ › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility
30. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating
31. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating
32. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating
33. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating
34. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating › Dependencies interface ChatClient { fun sendMessage(message: Message): Message }
35. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating › Dependencies interface ChatClient { suspend fun sendMessage(message: Message): Message }
36. Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating › Dependencies interface ChatClient { fun sendMessage(message: Message): Single<Message> }
37. 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>
38. Dependencies
39. Dependencies › Minimal dependencies
40. Dependencies › Minimal dependencies › Size
41. Dependencies Install conversion rate increase per 10MB decrease in APK size by select market (Google internal data, late 2017) › Minimal dependencies › Size
42. Dependencies › Minimal dependencies › Size › Many libraries per app Install conversion rate increase per 10MB decrease in APK size by select market (Google internal data, late 2017)
43. Dependencies › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps
44. Dependencies › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps › Complexity
45. Dependencies › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps › Complexity › Version conflicts
46. 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
47. Dependencies › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps › Complexity › Version conflicts Library 2 Library 1 Appcompat 1.4 alpha Appcompat 1.2 App
48. Dependencies › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps › Complexity › Version conflicts Library 1 Appcompat 1.4 alpha Appcompat 1.2 App Library 2
49. Version updates
50. Version updates
51. implementation vs api Library 1 App
52. implementation vs api Library 1 Library 2 App implementation
53. implementation vs api Library 1 Library 2 App api Library 1 Library 2 App implementation
54. library.aar
55. library.aar resources layout.xml values.xml
56. library.aar resources layout.xml values.xml AndroidManifest.xml
57. library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar
58. library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt
59. library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt library- sources.jar library- javadoc.jar *.kt *.html
60. 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
61. 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>
62. 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>
63. 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>
64. Repositories MavenCentral Library 1
65. Repositories MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
66. Repositories MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
67. Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
68. Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
69. Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
70. Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1
71. Multi-module libraries my-awesome-lib
72. Multi-module libraries my-awesome-lib
73. Multi-module libraries my-awesome-lib my-awesome-lib-plus my-awesome-lib-core
74. Multi-module libraries my-awesome-lib-plus my-awesome-lib-core my-awesome-lib
75. rx Multi-module libraries my-awesome-lib-plus my-awesome-lib-core
76. Multi-module libraries plus rxjava my-awesome-lib-rx my-awesome-lib-core
77. Fat AARs ui-components core offline client
78. Fat AARs ui-components core offline client App
79. Fat AARs ui-components core offline client App
80. Fat AARs ui-components core offline client App
81. Fat AARs
82. Fat AARs
83. Fat AARs
84. Fat AARs
85. 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
86. Fat AARs android-fat-aar adwiv/android-fat-aar
87. Fat AARs android-fat-aar adwiv/android-fat-aar
88. Fat AARs fat-aar-plugin vigidroid/fat-aar-plugin android-fat-aar adwiv/android-fat-aar
89. Fat AARs fat-aar-plugin vigidroid/fat-aar-plugin android-fat-aar adwiv/android-fat-aar
90. Fat AARs fat-aar-plugin vigidroid/fat-aar-plugin fataar-gradle-plugin Mobbeel/fataar-gradle-plugin android-fat-aar adwiv/android-fat-aar
91. Fat AARs fat-aar-plugin vigidroid/fat-aar-plugin fataar-gradle-plugin Mobbeel/fataar-gradle-plugin android-fat-aar adwiv/android-fat-aar
92. 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
93. Startup impact
94. Startup impact › Don’t hog startup › Competing with other libraries
95. Startup impact › Don’t hog startup › Competing with other libraries › Initialize on-demand
96. Startup impact › Don’t hog startup › Competing with other libraries › Initialize on-demand › App Startup
97. Logging
98. Logging › Don’t log by default
99. Logging › Don’t log by default val client = ChatClient.Builder("apiKey", context) .logLevel(ChatLogLevel.ALL) .build()
100. Logging › Don’t log by default › Don’t enable any feature by default val client = ChatClient.Builder("apiKey", context) .logLevel(ChatLogLevel.ALL) .build()
101. Performance › Minimize your impact › You’re in the inner loop › You’re in a lot of apps
102. Requirements › Minimal requirements › Make integrating your library easy › Don’t force things on your clients
103. API level App Library 1 Library 2 Library 3 API 21 API 21 API 19 API 15
104. API level App Library 1 Library 2 Library 3 API 21 API 21 API 19 API 15
105. API level App Library 1 Library 2 Library 3 API 21 API 21 API 23 API 15
106. API level App Library 1 Library 2 Library 3 API 23 API 21 API 23 API 15
107. Permissions & features library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt
108. 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
109. 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
110. <?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
111. <?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
112. <?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
113. Resource prefixes android { resourcePrefix 'stream_ui_' }
114. 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_' }
115. 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
116. 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' ?
117. 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>
118. Resource prefixes android { resourcePrefix 'stream_ui_' }
119. Private resources
120. 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>
121. 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>
122. Proguard library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt
123. 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
124. 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
125. 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
126. Proguard android { buildTypes { release { proguardFiles getDefaultProguardFile('proguard-android-optimize.txt’), 'proguard-rules.pro' consumerProguardFiles 'consumer-proguard-rules.pro' } debug { consumerProguardFiles 'consumer-proguard-rules.pro' } } }
127. Proguard android { buildTypes { release { proguardFiles getDefaultProguardFile('proguard-android-optimize.txt’), 'proguard-rules.pro' consumerProguardFiles 'consumer-proguard-rules.pro' } debug { consumerProguardFiles 'consumer-proguard-rules.pro' } } }
128. Proguard android { buildTypes { release { proguardFiles getDefaultProguardFile('proguard-android-optimize.txt’), 'proguard-rules.pro' consumerProguardFiles 'consumer-proguard-rules.pro' } debug { consumerProguardFiles 'consumer-proguard-rules.pro' } } }
129. Testing
130. Testing › Lots of responsibility
131. Testing › Lots of responsibility › Diverse environments
132. Testing › Lots of responsibility › Diverse environments › Can’t assume anything
133. Testing › Lots of responsibility › Diverse environments › Can’t assume anything › Devices, architectures, OS versions, stores
134. Testing › Lots of responsibility › Diverse environments › Can’t assume anything › Devices, architectures, OS versions, stores › Other frameworks and libraries
135. Testing › Lots of responsibility › Diverse environments › Can’t assume anything › Devices, architectures, OS versions, stores › Other frameworks and libraries › Your code is not final
136. Documentation
137. Documentation › Have documentation
138. Documentation › Have documentation › README
139. Documentation › Have documentation › README › What it does
140. Documentation › Have documentation › README › What it does › Setup instructions
141. Documentation › Have documentation › README › What it does › Setup instructions › Screenshots
142. Documentation › Have documentation › README › Code comments
143. Documentation › Have documentation › README › Code comments
144. Documentation › Have documentation › README › Code comments
145. Documentation › Have documentation › README › Code comments › Sample app
146. Documentation › Have documentation › README › Code comments › Sample app › Update strategy
147. Publishing
148. Publishing › Maven repositories
149. Publishing › Maven repositories › Main options
150. Publishing › Maven repositories › Main options › Jcenter
151. Publishing › Maven repositories › Main options › Jcenter
152. Publishing › Maven repositories › Main options › Jcenter
153. Publishing › Maven repositories › Main options › Jcenter
154. Publishing › Maven repositories › Main options › Jcenter › Jitpack
155. Publishing › Maven repositories › Main options › Jcenter › Jitpack
156. Publishing › Maven repositories › Main options › Jcenter › Jitpack › Maven Central
157. Publishing › Maven repositories › Main options › Jcenter › Jitpack › Maven Central
158. Publishing › Coordinates
159. Publishing › Coordinates io.getstream:stream-chat-android-client:4.12.0
160. Publishing › Coordinates io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID
161. Publishing Group ID io.getstream : stream-chat-android-client : 4.12.0 Version Artifact ID › Coordinates
162. Publishing › Coordinates io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID
163. Publishing › Coordinates › Versioning io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID
164. Publishing › Coordinates › Versioning semver.org io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID
165. Publishing › Coordinates › Versioning › License
166. Publishing › Coordinates › Versioning › License tldrlegal.com
167. Release checklist
168. Community
169. Community › Open source vs source available
170. Community › Open source vs source available › Address issues and discussions
171. Community › Open source vs source available › Address issues and discussions › Take PR contributions
172. Community › Open source vs source available › Address issues and discussions › Take PR contributions › Be open for feedback*
173. 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
174. 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
175. 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
176. zsmb13 zsmb.co/talks
177. 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!