Migrating from Fragments to Jetpack Compose with Nibel

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About me ● Google Developer Expert - Android, Kotlin ● Sr. Staff Software Engineer at Turo 2

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Problem?

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Problem? ● You have a codebase that relies on Fragments 4

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Problem? ● You have a codebase that relies on Fragments ● Adopting Jetpack Compose 5

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Problem? ● You have a codebase that relies on Fragments ● Adopting Jetpack Compose ● Gradual transition 6

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Problem? class FooFragment : Fragment() { ... } @Composable fun BarScreen() { ... } 7

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Navigation scenarios ● fragment → compose 8

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Navigation scenarios ● fragment → compose ● compose → compose 9

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Navigation scenarios ● fragment → compose ● compose → compose ● compose → fragment 10

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Problem? ● Uniﬁed navigation mechanism ● Proper Jetpack Compose experience 11

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Jetpack Compose architecture

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Jetpack Compose architecture ● Developed internally at Turo ● Now, open-source: https://github.com/open-turo/nibel 13

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Basic navigation

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Declaring an entry @UiEntry(type = ImplementationType.Fragment) @Composable fun FooScreen() { ... } 15

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Navigating fragment to compose

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Navigating fragment to compose class BarFragment : Fragment() { requireActivity().supportFragmentManager.commit { val entry = FooScreenEntry.newInstance().fragment replace(android.R.id.content, entry.fragment) } } 17

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Navigating compose to compose

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Navigating compose to compose @UiEntry(type = ImplementationType.Fragment) @Composable fun FooScreen() { ... } 20

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Navigating compose to compose @UiEntry(type = ImplementationType.Fragment) @Composable fun FooScreen() { ... } @UiEntry( type = ImplementationType.Composable, args = BarScreenArgs::class ) @Composable fun BarScreen(args: BarScreenArgs) { ... } 21

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Navigating compose to compose @UiEntry(type = ImplementationType.Fragment) @Composable fun FooScreen(navigator: NavigationController) { val args = BarArgs(...) navigator.navigateTo(BarScreenEntry.newInstance(args)) } 22

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Navigating compose to fragment

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Navigating compose to fragment 26 class BazFragment : Fragment() { ... }

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Navigating compose to fragment 27 @UiEntry(type = ImplementationType.Fragment) @Composable fun FooScreen(navigator: NavigationController) { val fragment = BazFragment() navigator.navigateTo(FragmentEntry(fragment)) }

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Navigating compose to fragment 28 @UiEntry(type = ImplementationType.Fragment) @Composable fun FooScreen(navigator: NavigationController) { val fragment = BazFragment() navigator.navigateTo(FragmentEntry(fragment)) }

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Thought process

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Wrap composable with a fragment 30 class FooFragment: Fragment() { override fun onCreateView( ... ) = ComposeView(requireContext()).apply { setContent { AppTheme { FooScreen() // <-- our composable function } } } }

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Wrap composable with a fragment 31 class FooFragment: Fragment() { val someState: SomeState override fun onCreateView(...) { ... } fun someNonComposeFunction() { ... } fun anotherNonComposeFunction() { ... } }

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Base fragment class 32 class FooFragment : ComposableFragment() { @Composable override fun ComposableContent() { FooScreen() // <-- our composable function } }

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ImplementationType.Fragment 33 @UiEntry(type = ImplementationType.Fragment) @Composable fun FooScreen() { ... }

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Generated fragment 34 // generated code class FooScreenEntry : ComposableFragment() { @Composable override fun ComposableContent() { FooScreen() // <-- our composable function } }

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Navigation 35 @UiEntry(type = ImplementationType.Fragment) @Composable fun FooScreen() { ... } @UiEntry(type = ImplementationType.Fragment) @Composable fun BarScreen() { ... }

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Navigation - fragment transaction 36 @UiEntry(type = ImplementationType.Fragment) @Composable fun FooScreen(navigator: NavigationController) { navigator.navigateTo(BarScreenEntry.newInstance()) } @UiEntry(type = ImplementationType.Fragment) @Composable fun BarScreen() { ... }

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Navigation - fragment transaction 37 @UiEntry(type = ImplementationType.Fragment) @Composable fun FooScreen(navigator: NavigationController) { navigator.navigateTo(BarScreenEntry.newInstance()) } @UiEntry(type = ImplementationType.Fragment) @Composable fun BarScreen() { ... }

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Optimization

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Generated composable wrapper 39 // generated code class BarEntry( override val args: SecondArgs, override val name: String, ) : ComposableEntry(args, name) { @Composable override fun ComposableContent() { BarScreen() // <-- our composable function } }

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Generated composable wrapper 40 // generated code class BarEntry( override val args: SecondArgs, override val name: String, ) : ComposableEntry(args, name) { @Composable override fun ComposableContent() { BarScreen() // <-- our composable function } }

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Implementation type 41 @UiEntry(type = ImplementationType.Fragment) @Composable fun FooScreen() { ... } @UiEntry(type = ImplementationType.Composable) @Composable fun BarScreen() { ... }

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Implementation type 42 navigator.navigateTo(BarScreenEntry.newInstance())

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Implementation type 43 navigator.navigateTo(BarScreenEntry.newInstance()) ???

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Abstraction over navigation

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Navigation under-the-hood 45 Fragment entry @Composable type.fragment

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Navigation under-the-hood 46 compose navigation @Composable entry @Composable Fragment entry @Composable type.fragment type.composable

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Navigation under-the-hood 47 @Composable entry @Composable Fragment entry @Composable compose navigation @Composable entry @Composable type.composable type.composable

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Navigation under-the-hood 48 @Composable entry @Composable Fragment entry @Composable fragment transaction @Composable entry @Composable Fragment (legacy) type.composable

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Navigation under-the-hood 49 Fragment entry @Composable fragment transaction Fragment (legacy)

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Navigation under-the-hood 50 @Composable entry @Composable Fragment entry @Composable fragment transaction @Composable entry @Composable Fragment (legacy) type.composable

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Navigation under-the-hood 51 // base class for generated fragments abstract class ComposableFragment : Fragment() { @Composable abstract fun ComposableContent() override fun onCreateView(...) = ComposeView(...).apply { setContent { AppTheme { ... NavHost(..., startDestination = "@root") { composable("@root") { ComposableContent() } } } } } }

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Navigation under-the-hood 52 // base class for generated fragments abstract class ComposableFragment : Fragment() { @Composable abstract fun ComposableContent() override fun onCreateView(...) = ComposeView(...).apply { setContent { AppTheme { ... NavHost(..., startDestination = "@root") { composable("@root") { ComposableContent() } } } } } }

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Navigation under-the-hood 53 // base class for generated fragments abstract class ComposableFragment : Fragment() { @Composable abstract fun ComposableContent() override fun onCreateView(...) = ComposeView(...).apply { setContent { AppTheme { ... NavHost(..., startDestination = "@root") { composable("@root") { ComposableContent() } } } } } }

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Navigation under-the-hood 54 // base class for generated fragments abstract class ComposableFragment : Fragment() { @Composable abstract fun ComposableContent() override fun onCreateView(...) = ComposeView(...).apply { setContent { AppTheme { ... NavHost(..., startDestination = "@root") { composable("@root") { ComposableContent() } } } } } }

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Navigation under-the-hood 55 // base class for generated fragments abstract class ComposableFragment : Fragment() { @Composable abstract fun ComposableContent() override fun onCreateView(...) = ComposeView(...).apply { setContent { AppTheme { ... NavHost(..., startDestination = "@root") { composable("@root") { ComposableContent() } } } } } }

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Navigation under-the-hood 56 // base class for generated fragments abstract class ComposableFragment : Fragment() { @Composable abstract fun ComposableContent() override fun onCreateView(...) = ComposeView(...).apply { setContent { AppTheme { ... NavHost(..., startDestination = "@root") { composable("@root") { ComposableContent() } } } } } }

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Demo

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Multi-module navigation

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Navigation module 59 feature A module feature B module

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Navigation module 60 navigation module feature A module feature B module depends depends

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61 screen 2 destination screen 1 screen 2 navigate to Navigation module

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Declaring a destination // :navigation module object FooScreenDestination : DestinationWithNoArgs 62

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Declaring a destination // :navigation module object FooScreenDestination : DestinationWithNoArgs data class BarScreenDestination( override val args: BarScreenArgs // Parcelable args ) : DestinationWithArgs 63

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Associating a destination with a screen @UiExternalEntry( type = ImplementationType.Fragment, destination = FooScreenDestination::class ) @Composable fun FooScreen() { ... } 64

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Navigating compose to compose

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Navigation compose to compose navigator.navigateTo(BarScreenDestination) 66

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Navigation compose to compose val args = BarScreenArgs(...) navigator.navigateTo(BarScreenDestination(args)) 67

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Navigating fragment to compose

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Navigation fragment to compose class BazScreenFragment : Fragment() { ... requireActivity().supportFragmentManager.commit { val entry = Nibel.newFragmentEntry(BarScreenDestination)!! replace(android.R.id.content, entry.fragment) } } 69

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Navigating compose to fragment

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Navigation fragment to compose @LegacyExternalEntry(destination = QuxScreenDestination::class) class QuxScreenFragment : Fragment() { ... } 73

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Navigation fragment to compose @LegacyExternalEntry(destination = BasScreenDestination::class) class BazScreenFragment : Fragment() { ... } navigator.navigateTo(BasScreenDestination) 74

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Jetpack Compose adoption scenarios

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Scenario 1: Brand new feature module

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77 Scenario 1 fragment @UiEntry type.composable @UiEntry type.composable new feature module @UiExternalEntry type.fragment

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78 Scenario 1 fragment @UiEntry type.composable @UiEntry type.composable new feature module @UiExternalEntry type.fragment

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79 Scenario 1 fragment @UiEntry type.composable @UiEntry type.composable new feature module @UiExternalEntry type.fragment

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80 Scenario 1 fragment @UiEntry type.composable @UiEntry type.composable new feature module @UiExternalEntry type.fragment

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81 Scenario 1 @UiEntry type.composable @UiEntry type.composable @UiExternalEntry type.fragment @LegacyExternalEntry fragment new feature module

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82 Scenario 1 @UiEntry type.composable @UiEntry type.composable @UiExternalEntry type.fragment @LegacyExternalEntry fragment new feature module

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83 Scenario 1 @UiEntry type.composable @UiEntry type.composable @UiExternalEntry type.fragment @LegacyExternalEntry fragment new feature module

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Scenario 2 Expanding existing feature

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85 Scenario 3 fragment @UiEntry type.composable fragment old feature module @UiEntry type.fragment

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86 Scenario 3 fragment @UiEntry type.composable fragment old feature module @UiEntry type.fragment

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Scenario 3 Standalone screens

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88 Scenario 3 fragment fragment old feature module @UiEntry type.fragment @UiEntry type.fragment

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89 Scenario 3 fragment fragment old feature module @UiEntry type.fragment @UiEntry type.fragment

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To conclude…

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To conclude... ● Abstract navigation fragment → compose, compose → fragment ● Simple API, no boilerplate ● High conﬁgurability 91

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Materials

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93 Blog posts medium.com/turo-engineering/ b11ee5f19ba8

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94 Blog posts medium.com/turo-engineering/ b11ee5f19ba8 medium.com/turo-engineering/ 541c7b2f3f84