How to Build Awesome Android Libraries (360 AnDev 2021)

by Márton Braun

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zsmb.co zsmb13 How to Build Awesome Android Libraries Márton Braun

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Introduction

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Introduction RainbowCake rainbowcake/rainbowcake Krate AutSoft/Krate MaterialDrawerKt zsmb13/MaterialDrawerKt requireKTX zsmb13/requireKTX

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GetStream/stream-chat-android › Open source chat SDK

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GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events

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GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events

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GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events › Offline support › Pre-built UI components

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GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events › Offline support › Pre-built UI components

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GetStream/stream-chat-android › Open source chat SDK › Low-level client with real-time events › Offline support › Pre-built UI components › Kotlin-first APIs

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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!

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GetStream/stream-chat-android

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TL;DW Minimize ALL the things!

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TL;DW Minimize ALL the things! › Features of the library

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TL;DW Minimize ALL the things! › Features of the library › Public API

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TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies

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TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies › Performance impact

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TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies › Performance impact › Enabled features by default

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TL;DW Minimize ALL the things! › Features of the library › Public API › Dependencies › Performance impact › Enabled features by default › Requirements

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Public API

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Public API › Minimal API

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Public API › Minimal API Item 15: Minimize the accessibility of classes and members

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Public API › Minimal API › Deprecations

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Public API › Minimal API › Deprecations

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Public API › Minimal API › Deprecations › Easy to use

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Public API › Minimal API › Deprecations › Easy to use › Hard to misuse

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Public API zsmb.co/talks/mastering-api-visibility/ › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility

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Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating

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Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating

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Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating › Dependencies interface ChatClient { suspend fun sendMessage(message: Message): Message }

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Public API › Minimal API › Deprecations › Easy to use › Hard to misuse › Controlling visibility › Validating › Dependencies public interface Call { public fun execute(): Result public fun enqueue(callback: Callback) } public suspend fun Call.await(): Result

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Dependencies

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Dependencies › Minimal dependencies

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Dependencies › Minimal dependencies › Size

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Dependencies › Minimal dependencies › Size › Many libraries per app

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Dependencies › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps

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Dependencies › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps › Complexity

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Dependencies › Minimal dependencies › Size › Many libraries per app › Library present in multiple apps › Complexity › Version conflicts

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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

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Version updates

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Version updates

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implementation vs api Library 1 App

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implementation vs api Library 1 Library 2 App implementation

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implementation vs api Library 1 Library 2 App implementation

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implementation vs api Library 1 Library 2 App api Library 1 Library 2 App implementation

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library.aar

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library.aar resources layout.xml values.xml

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library.aar resources layout.xml values.xml AndroidManifest.xml

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library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar

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library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt

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library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt library- sources.jar library- javadoc.jar *.kt *.html

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The POM file library.pom io.getstream stream-chat-android-client 4.12.0 aar stream-chat-android-client org.jetbrains.kotlin kotlin-stdlib 1.5.10 runtime ... library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt library- sources.jar library- javadoc.jar *.kt *.html

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The POM file library.pom io.getstream stream-chat-android-client 4.12.0 aar stream-chat-android-client org.jetbrains.kotlin kotlin-stdlib 1.5.10 runtime ...

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The POM file library.pom io.getstream stream-chat-android-client 4.12.0 aar stream-chat-android-client org.jetbrains.kotlin kotlin-stdlib 1.5.10 runtime ...

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The POM file library.pom io.getstream stream-chat-android-client 4.12.0 aar stream-chat-android-client org.jetbrains.kotlin kotlin-stdlib 1.5.10 runtime ...

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Repositories MavenCentral Library 1

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Repositories MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1

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Repositories MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1

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Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1

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Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1

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Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1

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Repositories App MavenCentral Jitpack Jcenter Library 3 Library 2 Library 1

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Multi-module libraries my-awesome-lib

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Multi-module libraries my-awesome-lib

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Multi-module libraries my-awesome-lib my-awesome-lib-plus my-awesome-lib-core

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Multi-module libraries my-awesome-lib-plus my-awesome-lib-core my-awesome-lib

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rx Multi-module libraries my-awesome-lib-plus my-awesome-lib-core

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Multi-module libraries plus rxjava my-awesome-lib-rx my-awesome-lib-core

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Fat AARs ui-components core offline client

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Fat AARs ui-components core offline client App

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Fat AARs ui-components core offline client App

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Fat AARs ui-components core offline client App

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Fat AARs

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Fat AARs

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Fat AARs

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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

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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

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Startup impact

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Startup impact › Don’t hog startup › Competing with other libraries

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Startup impact › Don’t hog startup › Competing with other libraries › Initialize on-demand

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Startup impact › Don’t hog startup › Competing with other libraries › Initialize on-demand › App Startup

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Logging

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Logging › Don’t log by default

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Logging › Don’t log by default val client = ChatClient.Builder("apiKey", context) .logLevel(ChatLogLevel.ALL) .build()

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Logging › Don’t log by default › Don’t enable any feature by default val client = ChatClient.Builder("apiKey", context) .logLevel(ChatLogLevel.ALL) .build()

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Requirements › Minimal requirements › Make integrating your library easy › Don’t force things on your clients

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API level App Library 1 Library 2 Library 3 API 21 API 21 API 19 API 15

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API level App Library 1 Library 2 Library 3 API 21 API 21 API 19 API 15

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API level App Library 1 Library 2 Library 3 API 21 API 21 API 23 API 15

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API level App Library 1 Library 2 Library 3 API 23 API 21 API 23 API 15

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Permissions & features library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt

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Permissions & features library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt

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Permissions & features AndroidManifest.xml

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Permissions & features AndroidManifest.xml

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Permissions & features AndroidManifest.xml

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Permissions & features AndroidManifest.xml

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Resource prefixes android { resourcePrefix 'stream_ui_' }

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Resource prefixes #005FFF #FF3742 #20E070 accent_green android { resourcePrefix 'stream_ui_' }

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Resource prefixes android { resourcePrefix 'stream_ui_' } #005FFF #FF3742 #20E070 accent_green

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Resource prefixes android { resourcePrefix 'stream_ui_' } #005FFF #FF3742 #20E070 accent_green Resource named 'accent_green' does not start with the project's resource prefix 'stream_ui_'; rename to 'stream_ui_accent_green' ?

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Resource prefixes android { resourcePrefix 'stream_ui_' }

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Resource prefixes android { resourcePrefix 'stream_ui_' }

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Private resources

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Private resources

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Explicitly public resources

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Proguard library.aar resources layout.xml values.xml AndroidManifest.xml classes.jar R.txt

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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

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Proguard android { buildTypes { release { proguardFiles getDefaultProguardFile('proguard-android-optimize.txt’), 'proguard-rules.pro' consumerProguardFiles 'consumer-proguard-rules.pro' } debug { consumerProguardFiles 'consumer-proguard-rules.pro' } } }

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Testing

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Testing › Lots of responsibility

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Testing › Lots of responsibility › Diverse environments

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Testing › Lots of responsibility › Diverse environments › Can’t assume anything

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Testing › Lots of responsibility › Diverse environments › Can’t assume anything › Devices, architectures, OS versions, stores

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Testing › Lots of responsibility › Diverse environments › Can’t assume anything › Devices, architectures, OS versions, stores › Other frameworks and libraries

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Testing › Lots of responsibility › Diverse environments › Can’t assume anything › Devices, architectures, OS versions, stores › Other frameworks and libraries › Your code is not final

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Documentation

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Documentation › Have documentation

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Documentation › Have documentation › README

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Documentation › Have documentation › README › What it does

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Documentation › Have documentation › README › What it does › Setup instructions

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Documentation › Have documentation › README › What it does › Setup instructions › Screenshots

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Documentation › Have documentation › README › Code comments

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Documentation › Have documentation › README › Code comments

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Documentation › Have documentation › README › Code comments

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Documentation › Have documentation › README › Code comments › Sample app

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Documentation › Have documentation › README › Code comments › Sample app › Update strategy

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Publishing

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Publishing › Maven repositories

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Publishing › Maven repositories › Main options

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Publishing › Maven repositories › Main options › Jcenter

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Publishing › Maven repositories › Main options › Jcenter

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Publishing › Maven repositories › Main options › Jcenter

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Publishing › Maven repositories › Main options › Jcenter

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Publishing › Maven repositories › Main options › Jcenter › Jitpack

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Publishing › Maven repositories › Main options › Jcenter › Jitpack

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Publishing › Maven repositories › Main options › Jcenter › Jitpack › Maven Central

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Publishing › Maven repositories › Main options › Jcenter › Jitpack › Maven Central

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Publishing › Coordinates

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Publishing › Coordinates io.getstream:stream-chat-android-client:4.12.0

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Publishing › Coordinates io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID

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Publishing Group ID io.getstream : stream-chat-android-client : 4.12.0 Version Artifact ID › Coordinates

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Publishing › Coordinates io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID

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Publishing › Coordinates › Versioning io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID

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Publishing › Coordinates › Versioning semver.org io.getstream : stream-chat-android-client : 4.12.0 Group ID Version Artifact ID

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Publishing › Coordinates › Versioning › License

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Publishing › Coordinates › Versioning › License tldrlegal.com

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Release checklist

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Community

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Community › Open source vs source available

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Community › Open source vs source available › Address issues and discussions

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Community › Open source vs source available › Address issues and discussions › Take PR contributions

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Community › Open source vs source available › Address issues and discussions › Take PR contributions › Be open for feedback*

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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

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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

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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

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zsmb13 zsmb.co/talks

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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!