Brick by Brick: Building Open Source libraries

So you have an idea, and you want to publish a library for it? But where do you start? Doing Open Source is a fine art which requires skill you don’t easily learn on schoolbooks. Creating a new library is like building a new house that people want to live in: you need to start with a great foundation, build your inner walls and then add all the niceties that make your house the best place to live in.

Join us as we share our journey building Open Source Android libraries: we’ll start from tools to help you organize your code, we’ll learn how to publish your libraries publicly and how to effectively maintain them. Throughout this journey, we’ll share our experience maintaining popular Android libraries such as Detekt, Chucker and AppIntro.

A house won’t be a home without someone living inside it, though. As your library won’t be a popular library without a strong community around it. So we’ll have the opportunity to share our insights on building strong communities around Open Source, getting developers together, finding new contributors and dealing with maintainer burnout.

Curious to know how to build a shiny new library brick by brick? Then make sure to don’t miss out this talk, and we can’t wait to see what you all will be building!

Transcript

1. PAOLO ROTOLO @paolorotolo NICOLA CORTI @cortinico
2. • Android Dev @ Nextome • AppIntro Author, Piano Player • twitter.com/paolorotolo • github.com/paolorotolo NICOLA CORTI PAOLO ROTOLO • Kotlin GDE • twitter.com/cortinico • github.com/cortinico
3. detekt/detekt ChuckerTeam/Chucker AppIntro/AppIntro
11. Learn to say no
12. Learn to say no • Build elegant APIs • Do not break APIs • Future proof your APIs
13. Learn to say no • Build elegant APIs • Do not break APIs • Future proof your APIs
14. Build elegant APIs list.first() list.firstOrNull() list.single() list.singleOrNull()
15. class DefaultIntro : AppIntro() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) addSlide(AppIntroFragment.createInstance( title = "Title 1", description = "Desc 1", imageDrawable = R.drawable.ic_slide1 )) addSlide(AppIntroFragment.createInstance( title = “Title 2", description = "Desc 2", imageDrawable = R.drawable.ic_slide2 )) setTransformer(AppIntroPageTransformerType.Fade) isWizardMode = true isColorTransitionsEnabled = true Build elegant APIs
16. AppIntroScreen { slides { slide { title = "Title 1" description = "Desc 1" imageDrawable = R.drawable.image1 backgroundColor = R.color.orange } slide { title = "Title 2" description = "Desc 2" imageDrawable = R.drawable.image2 backgroundColor = R.color.blue } } settings { transformer = transformer { AppIntroPageTransformerType. } isWizardMode = true Fade Build elegant APIs
17. /** * Sealed class to represent all the possible Page Transformers * offered by AppIntro. */ sealed class AppIntroPageTransformerType { object Flow : AppIntroPageTransformerType() object Depth : AppIntroPageTransformerType() object Zoom : AppIntroPageTransformerType() object SlideOver : AppIntroPageTransformerType() object : AppIntroPageTransformerType() class Parallax( val titleParallaxFactor: Double = 1.0, val imageParallaxFactor: Double = -1.0, val descriptionParallaxFactor: Double = 2.0, @IdRes val titleViewId: Int = R.id.title, @IdRes val imageViewId: Int = R.id.image, @IdRes val descriptionViewId: Int = R.id.description ) : AppIntroPageTransformerType() } Fade Build elegant APIs
18. when (transformType) { AppIntroPageTransformerType.Flow -> { page.rotationY = position * FLOW_ROTATION_ANGLE } AppIntroPageTransformerType.SlideOver -> transformSlideOver(position, page) AppIntroPageTransformerType.Depth - > transformDepth(position, page) AppIntroPageTransformerType.Zoom -> transformZoom(position, page) AppIntroPageTransformerType.Fade -> transformFade(position, page) is AppIntroPageTransformerType.Parallax -> { titlePF = transformType.titleParallaxFactor imagePF = transformType.imageParallaxFactor descriptionPF = transformType.descriptionParallaxFactor transformParallax( position, page, transformType.titleViewId, transformType.imageViewId, transformType.descriptionViewId ) } } Build elegant APIs
19. class DefaultIntro : AppIntro() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) addSlide( AppIntroFragment.createInstance( title = "Welcome!", description = "This is a demo of the AppIntro library", imageDrawable = R.drawable.ic_slide1 ) ) Build elegant APIs
20. class DefaultIntro : AppIntro() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) addSlide( AppIntroFragment.createInstance( title = "Welcome!", description = "This is a demo of the AppIntro library", imageDrawable = R.drawable.ic_slide1 ) ) Build elegant APIs
21. addSlide( AppIntroFragment.createInstance( title = "Welcome!", description = "This is a demo of the AppIntro library", imageDrawable = R.drawable.ic_slide1 ) ) Build elegant APIs
22. addSlide( AppIntroCustomLayoutFragment.newInstance( R.layout.intro_custom_layout1 ) ) Build elegant APIs
23. Learn to say no • Build elegant APIs • Do not break APIs • Future proof your APIs
24. abstract class AppIntro : AppIntroBase() { override val layoutId = R.layout.appintro_intro_layout /** * Override viewpager bar color * @param color your color resource */ fun setBarColor(@ColorInt color: Int) { val bottomBar = findViewById<View>(R.id.bottom) bottomBar.setBackgroundColor(color) } Do not break APIs
25. public abstract class AppIntro : AppIntroBase() { override val layoutId = R.layout.appintro_intro_layout /** * Override viewpager bar color * @param color your color resource */ public fun setBarColor(@ColorInt color: Int) { val bottomBar = findViewById<View>(R.id.bottom) bottomBar.setBackgroundColor(color) } Do not break APIs Kotlin Explicit API mode
26. public abstract class AppIntro : AppIntroBase() { override val layoutId: Int = R.layout.appintro_intro_layout /** * Override viewpager bar color * @param color your color resource */ public fun setBarColor(@ColorInt color: Int) { val bottomBar = findViewById<View>(R.id.bottom) bottomBar.setBackgroundColor(color) } Do not break APIs Kotlin Explicit API mode
27. fun goToSlide( number: Int ) { TODO() } Do not break APIs
28. fun goToSlide( number: Int, animate: Boolean, ) { TODO() } Do not break APIs
29. fun goToSlide( number: Int, animate: Boolean = false, ) { TODO() } Do not break APIs
30. fun goToSlide( number: Int, animate: Boolean = false, ) { TODO() } void goToSlide(Integer number, boolean animate); Do not break APIs
31. fun goToSlide( number: Int, animate: Boolean = false, ) { TODO() } void goToSlide(Integer number, boolean animate); @JvmOverloads void goToSlide(Integer number); Do not break APIs
32. Don’t use Data Classes in public APIs Do not break APIs
33. bit.ly/brokenapi Do not break APIs
34. @Deprecated( level = DeprecationLevel.WARNING ) fun newInstance(sliderPage: SliderPage) = createInstance(sliderPage) replaceWith = ReplaceWith("createInstance(sliderPage)"), message = "`newInstance` is deprecated to support color resources instead of color int " + "for configuration changes and dark theme support", Do not break APIs
35. @Deprecated( level = DeprecationLevel.WARNING ) fun newInstance(sliderPage: SliderPage) = createInstance(sliderPage) replaceWith = ReplaceWith("createInstance(sliderPage)"), message = "`newInstance` is deprecated to support color resources instead of color int " + "for configuration changes and dark theme support", Do not break APIs
36. @Deprecated( level = DeprecationLevel.WARNING ) fun newInstance(sliderPage: SliderPage) = createInstance(sliderPage) replaceWith = ReplaceWith("createInstance(sliderPage)"), message = "`newInstance` is deprecated to support color resources instead of color int " + "for configuration changes and dark theme support", Do not break APIs
38. @Deprecated( level = DeprecationLevel.WARNING ) fun newInstance(sliderPage: SliderPage) = createInstance(sliderPage) replaceWith = ReplaceWith("createInstance(sliderPage)"), message = "`newInstance` is deprecated to support color resources instead of color int " + "for configuration changes and dark theme support", Do not break APIs
39. DeprecationLevel.WARNING DeprecationLevel.ERROR DeprecationLevel.HIDDEN Do not break APIs
40. <?xml version="1.0" encoding="utf-8"?> <resources xmlns:tools="http: // schemas.android.com/tools"> <string name="skip_button">SKIP </ string> <string name="next_button">NEXT </ string> <string name="back_button">BACK </ string> <string name="done_button">DONE </ string> </ resources> Don’t forget about Resources Do not break APIs
41. <?xml version="1.0" encoding="utf-8"?> <resources xmlns:tools="http: // schemas.android.com/tools"> <string name="app_intro_skip_button">SKIP </ string> <string name="app_intro_next_button">NEXT </ string> <string name="app_intro_back_button">BACK </ string> <string name="app_intro_done_button">DONE </ string> </ resources> Do not break APIs Don’t forget about Resources
42. Learn to say no • Build elegant APIs • Do not break APIs • Future proof your APIs
43. Retrofit Room Joda Time Timber Moshi Paging - > - > - > - > - > - > Ktor SQLDelight DataTime Kermit kotlinx-serialization Cash App’s Paging Future proof your APIs
44. Avoid asking for Context in public APIs Future proof your APIs
45. let myLib = MyLibrary.getInstance() myLib.doSomething() val myLib = MyLibrary.getInstance( applicationContext) myLib.doSomething() Future proof your APIs
46. let myLib = MyLibrary.getInstance() myLib.doSomething() val myLib = MyLibrary.getInstance() myLib.doSomething() Future proof your APIs
47. let myLib = MyLibrary.getInstance() myLib.doSomething() val myLib = MyLibrary.getInstance() myLib.doSomething() bit.ly/AvoidAskingForContext Future proof your APIs
49. JitPack GitHub Packages Maven Central
50. JitPack
51. JitPack • Easy to use • Free for OSS • Good for starting • No support for artifacts signing • No support for Kotlin Multiplatform (yet)
52. JitPack • Easy to use • Free for OSS • Good for starting • No support for artifacts signing • No support for Kotlin Multiplatform (yet) jitpack/jitpack.io #3853
53. GitHub Packages
54. GitHub Packages • Easy integration with Actions • Code and artifacts on the same repo • Supports Kotlin Multiplatform • Users are required to login with a token
55. dependencyResolutionManagement { repositories { google() mavenCentral() maven { name = "GitHubPackages" url = uri("https: // maven.pkg.github.com/Nextome/KmmBeacons") credentials { username = "gh_username" password = "gh_token" } } } } settings.gradle (user)
56. dependencyResolutionManagement { repositories { google() mavenCentral() maven { name = "GitHubPackages" url = uri("https: // maven.pkg.github.com/Nextome/KmmBeacons") credentials { username = "gh_username" password = "gh_token" } } } } settings.gradle (user)
57. Maven Central
58. Maven Central • Popular, included by default in Android projects • Open Source Software Repository Hosting (OSSRH) for free • More secure • Requires more effort and time to set up
59. Don’t reinvent the wheel
60. github.com/cortinico/kotlin-android-template Don’t reinvent the wheel
61. Gradle Source Dependencies Bonus
62. sourceControl { gitRepository(URI("https: // github.com/AppIntro/AppIntro.git")) { producesModule("com.github.AppIntro:AppIntro") rootDir = "appintro" } } settings.gradle Gradle Source Dependencies
63. sourceControl { gitRepository(URI("https: // github.com/AppIntro/AppIntro.git")) { producesModule("com.github.AppIntro:AppIntro") rootDir = "appintro" } } settings.gradle implementation("com.github.AppIntro:AppIntro:SNAPSHOT") { version { branch = "main" } } build.gradle Gradle Source Dependencies
64. sourceControl { gitRepository(URI("https: / producesModule("com.github.AppIntro:AppIntro") rootDir = "appintro" } } settings.gradle implementation("com.github.AppIntro:AppIntro:SNAPSHOT") { version { branch = "main" } } build.gradle Gradle Source Dependencies
65. We are getting there. help voting bit.ly/gradlesourcedeps Gradle Source Dependencies
66. Tell the world
70. Setting the right expectations
71. • Follow a schema • Feature-based • Release-train • ROADMAP.md fi le Predictable Releases
72. Conventional Commits
73. Conventional Commits
74. Keepachangelog
75. SemVer MAJOR.MINOR.PATCH Breaking! New Feature! Bug fi x!
76. • Have a stable CI • 3rd-party dependency bumps Maintain the Codebase
77. • Have a stable CI • 3rd-party dependency bumps Maintain the Codebase
78. • Have a stable CI • 3rd-party dependency bumps Maintain the Codebase
81. • Stalebot • Code of Conduct • Interaction Limits • Danger Maintain the Repository
82. Danger & PR Automations
83. Danger & PR Automations
84. Danger & PR Automations
85. Danger & PR Automations
86. Danger & PR Automations
88. Understand your growth model
89. Growth High User Growth Low User Growth High Contributor Growth Low Contributor Growth
90. High User Growth Low User Growth High Contributor Growth Federations (Flutter) Low Contributor Growth Growth
91. High User Growth Low User Growth High Contributor Growth Federations (Flutter) Low Contributor Growth Stadium (OkHTTP) Growth
92. High User Growth Low User Growth High Contributor Growth Federations (Flutter) Clubs (Arrow) Low Contributor Growth Stadium (OkHTTP) Growth
93. High User Growth Low User Growth High Contributor Growth Federations (Flutter) Clubs (Arrow) Low Contributor Growth Stadium (OkHTTP) Toys Growth
94. • First, what’s your model? • Start a chat channel • KotlinLang Slack • Discord • Twitter pro fi le Grow your community
95. • Run contests • Join Hacktoberfest • Organize Meet-ups • Swag-as-a-service Gamify your contributions
96. • Github Sponsors • OpenCollective • thanks.dev Grow your sponsors
98. PAOLO ROTOLO @paolorotolo NICOLA CORTI @cortinico Thank you!