Lessons learned decoupling Architecture Components from platform specific code

Follow along as the Android team walks you through the process of taking some of their architectural building blocks, such as SavedState and System Back, through the process of decoupling them from platform specific implementations and how they approached the task of writing good common APIs in preparation for future integrations with other platforms while maintaining the quality achieved in android.

Transcript

1. Lessons learned decoupling Architecture Components from platform specific code Jeremy Woods, Marcello Galhardo linkedIn@jeremybwoods 🦋 @marcellogalhardo.dev
2. Architecture Components Team
3. • 6 people across 3 countries. Architecture Components Team
4. • 6 people across 3 countries. • 12 different libraries ◦ Activity, DataStore, Fragment, Hilt, Lifecycle, Navigation, Paging, Room, SavedState, ViewModel, SQLite, XProcessing Architecture Components Team • 6 people across 3 countries.
5. • 6 people across 3 countries. • 14 different libraries ◦ Lifecycle, SavedState, ViewModel. Navigation, Activity, Fragment, Room, DataStore, Paging, Dagger Hilt, SQLite, XProcessing. ◦ Navigation3, NavigationEvent Architecture Components Team • 6 people across 3 countries. • 1 different libraries ◦ Activity, DataStore, Fragment, Hilt, Lifecycle, Navigation, Paging, Room, SavedState, ViewModel, SQLite, XProcessing
6. Today’s agenda 01 02 03 04
7. Today’s agenda Motivation: why KMP? 01 02 03 04
8. Today’s agenda Motivation: why KMP? 01 Migrating an existing library 02 03 04
9. Today’s agenda Motivation: why KMP? 01 Migrating an existing library 02 Creating a new library 03 04
10. Today’s agenda Motivation: why KMP? 01 Migrating an existing library 02 Creating a new library 03 04 Review
11. Proprietary + Confidential 01 Motivation: why KMP?
12. Why KMP?
13. • Android is Kotlin-first (since 2019). Why KMP?
14. • Android is Kotlin-first (since 2019). • Code sharing across native platforms. Why KMP? • Android is Kotlin-first (since 2019).
15. • Android is Kotlin-first (since 2019). • Code sharing across native platforms. • Help building the ecosystem. Why KMP? • Android is Kotlin-first (since 2019). • Code sharing across native platforms.
16. AndroidX Arch KMP Libraries
17. AndroidX Arch KMP Libraries
18. AndroidX Arch KMP Libraries
19. Proprietary + Confidential 02 Migrating an existing library
20. • Used to save and restore state in a process death. • First alpha released in December 2018, written in Java. • KMP-compatible release in May 2025 (1.3.0). AndroidX SavedState
21. Core Components
22. Core Components
23. How these APIs look?
24. public class SavedStateRegistryController { public val savedStateRegistry: SavedStateRegistry public fun performRestore(savedState: Bundle?) public fun performSave(outBundle: Bundle) // {...} }
25. public class SavedStateRegistryController { public val savedStateRegistry: SavedStateRegistry public fun performRestore(savedState: Bundle?) public fun performSave(outBundle: Bundle) // {...} }
26. public class SavedStateRegistryController { public val savedStateRegistry: SavedStateRegistry public fun performRestore(savedState: Bundle?) public fun performSave(outBundle: Bundle) // {...} }
27. public class SavedStateRegistry { public fun consumeRestoredStateForKey(key: String): Bundle? public fun registerSavedStateProvider(key: String, provider: SavedStateProvider) public fun interface SavedStateProvider { public fun saveState(): Bundle } // {...} }
28. public class SavedStateRegistry { public fun consumeRestoredStateForKey(key: String): Bundle? public fun registerSavedStateProvider(key: String, provider: SavedStateProvider) public fun interface SavedStateProvider { public fun saveState(): Bundle } // {...} }
29. public class SavedStateRegistry { public fun consumeRestoredStateForKey(key: String): Bundle? public fun registerSavedStateProvider(key: String, provider: SavedStateProvider) public fun interface SavedStateProvider { public fun saveState(): Bundle } // {...} }
30. class ComponentActivity : Activity() { val controller = SavedStateRegistryController.create(owner = this) override fun onCreate(savedInstanceState: Bundle?) { controller.performRestore(savedInstanceState) // {...} } override fun onSaveInstanceState(outState: Bundle) { // {...} controller.performSave(outState) } }
31. class ComponentActivity : Activity() { val controller = SavedStateRegistryController.create(owner = this) override fun onCreate(savedInstanceState: Bundle?) { controller.performRestore(savedInstanceState) // {...} } override fun onSaveInstanceState(outState: Bundle) { // {...} controller.performSave(outState) } }
32. class ComponentActivity : Activity() { val controller = SavedStateRegistryController.create(owner = this) override fun onCreate(savedInstanceState: Bundle?) { controller.performRestore(savedInstanceState) // {...} } override fun onSaveInstanceState(outState: Bundle) { // {...} controller.performSave(outState) } }
33. // Or a more high-level API. class MyViewModel( private val handle: SavedStateHandle, ) : ViewModel() { val name = handle.getMutableStateFlow(“key”) { “John Doe” } }
34. Why?
35. Top 50k apps using SavedState
36. class Bundle { constructor(capacity: Int) constructor(b: Bundle?) constructor(persistableBundle: PersistableBundle) fun putAll(bundle: Bundle) fun size(): Int fun isEmpty(): Boolean fun clear() public override fun clone(): Any fun putBoolean(key: String, value: Boolean) fun putByte(key: String, value: Byte) fun putChar(key: String, value: Char) fun putShort(key: String, value: Short) fun putInt(key: String, value: Int) fun putLong(key: String, value: Long) fun putFloat(key: String, value: Float) fun putDouble(key: String, value: Double) fun putString(key: String, value: String?) fun putCharSequence(key: String, value: CharSequence?) fun putParcelable(key: String, value: Parcelable?) fun putParcelableArray(key: String, value: Array<Parcelable?>?) fun putParcelableArrayList(key: String, value: ArrayList<out Parcelable>?) fun putSparseParcelableArray(key: String, value: android.util.SparseArray<out Parcelable>?) fun putSerializable(key: String, value: Serializable?) fun putIntegerArrayList(key: String, value: ArrayList<Int>?) fun putStringArrayList(key: String, value: ArrayList<String>?) fun putCharSequenceArrayList(key: String, value: ArrayList<CharSequence>?) fun putBundle(key: String, value: Bundle?) fun putBooleanArray(key: String, value: BooleanArray?) fun putByteArray(key: String, value: ByteArray?) fun putShortArray(key: String, value: ShortArray?) fun putCharArray(key: String, value: CharArray?) fun putIntArray(key: String, value: IntArray?) fun putLongArray(key: String, value: LongArray?) fun putFloatArray(key: String, value: FloatArray?) fun putDoubleArray(key: String, value: DoubleArray?) fun putStringArray(key: String, value: Array<String?>?) fun putCharSequenceArray(key: String, value: Array<CharSequence?>?) fun putParcelableArray(key: String, value: Array<Parcelable?>?) fun putSize(key: String, value: Size?) fun putSizeF(key: String, value: SizeF?) fun getBoolean(key: String): Boolean fun getBoolean(key: String, defaultValue: Boolean): Boolean fun getByte(key: String): Byte fun getByte(key: String, defaultValue: Byte): Byte fun getChar(key: String): Char fun getChar(key: String, defaultValue: Char): Char fun getShort(key: String): Short fun getShort(key: String, defaultValue: Short): Short fun getInt(key: String): Int fun getInt(key: String, defaultValue: Int): Int fun getLong(key: String): Long fun getLong(key: String, defaultValue: Long): Long fun getFloat(key: String): Float fun getFloat(key: String, defaultValue: Float): Float fun getDouble(key: String): Double fun getDouble(key: String, defaultValue: Double): Double fun getString(key: String): String? fun getCharSequence(key: String): CharSequence? fun <T : Parcelable?> getParcelable(key: String): T? fun <T : Parcelable?> getParcelableArray(key: String): Array<T?>? fun <T : Parcelable?> getParcelableArrayList(key: String): ArrayList<T>? fun <T : Parcelable?> getSparseParcelableArray(key: String): android.util.SparseArray<T>? fun getSerializable(key: String): Serializable? fun getIntegerArrayList(key: String): ArrayList<Int>? fun getStringArrayList(key: String): ArrayList<String>? fun getCharSequenceArrayList(key: String): ArrayList<CharSequence>? fun getBundle(key: String): Bundle? fun getBooleanArray(key: String): BooleanArray? fun getByteArray(key: String): ByteArray? fun getShortArray(key: String): ShortArray? fun getCharArray(key: String): CharArray? fun getIntArray(key: String): IntArray? fun getLongArray(key: String): LongArray? fun getFloatArray(key: String): FloatArray? fun getDoubleArray(key: String): DoubleArray? fun getStringArray(key: String): Array<String?>? fun getCharSequenceArray(key: String): Array<CharSequence?>? fun getSize(key: String): Size? fun getSizeF(key: String): SizeF? fun containsKey(key: String): Boolean fun remove(key: String) fun keySet(): Set<String> }
37. public class SavedStateRegistryController { // {...} public fun performRestore(savedState: Bundle?) public fun performSave(outBundle: Bundle) // {...} }
38. public class SavedStateRegistryController { // {...} public fun performRestore(savedState: Bundle?) public fun performSave(outBundle: Bundle) // {...} }
40. Android Framework Team !== AndroidX Team
41. “Extension is shadowed by a member”
42. Zero-cost abstraction
43. public class SavedStateRegistryController { // {...} public fun performRestore(savedState: Bundle?) public fun performSave(outBundle: Bundle) // {...} }
44. public class SavedStateRegistryController { // {...} public fun performRestore(savedState: SavedState?) public fun performSave(outBundle: SavedState) // {...} }
45. Expect Actual
46. // commonMain public expect class SavedState // androidMain public actual typealias SavedState = android.os.Bundle // nonAndroidMain public actual class SavedState(map: MutableMap<String, Any?>)
47. // commonMain public expect class SavedState // androidMain public actual typealias SavedState = android.os.Bundle // nonAndroidMain public actual class SavedState(map: MutableMap<String, Any?>)
48. // commonMain public expect class SavedState // androidMain public actual typealias SavedState = android.os.Bundle // nonAndroidMain public actual class SavedState(map: MutableMap<String, Any?>)
49. public expect inline fun savedState(block: SavedStateWriter.() -> Unit): SavedState @JvmInline public expect value class SavedStateReader(source: SavedState) // {...} public inline fun <T> SavedState.read(block: SavedStateReader.() -> T): T // {...} @JvmInline public expect value class SavedStateWriter(source: SavedState) // {...} public inline fun <T> SavedState.write(block: SavedStateWriter.() -> T): T // {...}
50. public expect inline fun savedState(block: SavedStateWriter.() -> Unit): SavedState @JvmInline public expect value class SavedStateReader(source: SavedState) // {...} public inline fun <T> SavedState.read(block: SavedStateReader.() -> T): T // {...} @JvmInline public expect value class SavedStateWriter(source: SavedState) // {...} public inline fun <T> SavedState.write(block: SavedStateWriter.() -> T): T // {...}
51. public expect inline fun savedState(block: SavedStateWriter.() -> Unit): SavedState @JvmInline public expect value class SavedStateReader(source: SavedState) // {...} public inline fun <T> SavedState.read(block: SavedStateReader.() -> T): T // {...} @JvmInline public expect value class SavedStateWriter(source: SavedState) // {...} public inline fun <T> SavedState.write(block: SavedStateWriter.() -> T): T // {...}
52. public expect inline fun savedState(block: SavedStateWriter.() -> Unit): SavedState @JvmInline public expect value class SavedStateReader(source: SavedState) // {...} public inline fun <T> SavedState.read(block: SavedStateReader.() -> T): T // {...} @JvmInline public expect value class SavedStateWriter(source: SavedState) // {...} public inline fun <T> SavedState.write(block: SavedStateWriter.() -> T): T // {...}
53. public expect inline fun savedState(block: SavedStateWriter.() -> Unit): SavedState @JvmInline public expect value class SavedStateReader(source: SavedState) // {...} public inline fun <T> SavedState.read(block: SavedStateReader.() -> T): T // {...} @JvmInline public expect value class SavedStateWriter(source: SavedState) // {...} public inline fun <T> SavedState.write(block: SavedStateWriter.() -> T): T // {...}
54. SavedState, Readers and Writers
55. data class Person(val name: String, val age: Int) val person = Person(“John Doe”, 21) val state = savedState { this: SavedStateWriter -> putString("name", person.name) putInt("age", person.age) } val name = state.read { this: SavedStateReader -> getString("name") }
56. data class Person(val name: String, val age: Int) val person = Person(“John Doe”, 21) val state = savedState { this: SavedStateWriter -> putString("name", person.name) putInt("age", person.age) } val name = state.read { this: SavedStateReader -> getString("name") }
57. data class Person(val name: String, val age: Int) val person = Person(“John Doe”, 21) val state = savedState { this: SavedStateWriter -> putString("name", person.name) putInt("age", person.age) } val name = state.read { this: SavedStateReader -> getString("name") }
58. KotlinX Serialization + Compose
61. data class Person(val name: String, val age: Int)
62. @Serializable data class Person(val name: String, val age: Int)
63. @Serializable data class Person(val name: String, val age: Int) fun main() { val person = Person("John Doe", 21) val encoded: SavedState = encodeToSavedState(person) val decoded: Person = decodeFromSavedState(encoded) }
64. @Serializable data class Person(val name: String, val age: Int) fun main() { val person = Person("John Doe", 21) val encoded: SavedState = encodeToSavedState(person) val decoded: Person = decodeFromSavedState(encoded) }
65. @Serializable data class Person(val name: String, val age: Int) fun main() { val person = Person("John Doe", 21) val encoded: SavedState = encodeToSavedState(person) val decoded: Person = decodeFromSavedState(encoded) }
66. @Serializable data class Person(val name: String, val age: Int) fun main() { val person = Person("John Doe", 21) val encoded: SavedState = encodeToSavedState(person) val decoded: Person = decodeFromSavedState(encoded) }
67. Bundle = [ "name": String = "John Doe", "age" : Int = 21, ]
68. @Serializable data class Person(val name: String, val age: Int) fun main() { val configuration = SavedStateConfiguration { serializersModule = SerializersModule {…} encodeDefaults = true classDiscriminatorMode = ClassDiscriminatorMode.POLYMORPHIC } val person = Person("John Doe", 21) val encoded: SavedState = encodeToSavedState(configuration, person) val decoded: Person = decodeFromSavedState(configuration encoded) }
69. @Serializable data class Person(val name: String, val age: Int) class MyViewModel(handle: SavedStateHandle) : ViewModel() { val person by handle.saved { Person("John Doe", 21) } }
70. @Serializable data class Person(val name: String, val age: Int) class MyComponent : SavedStateRegistryOwner { val person by saved { Person("John Doe", 21) } }
71. @Serializable data class Person(val name: String, val age: Int) class MyActivity : ComponentActivity() { val person by saved { Person("John Doe", 21) } }
72. @Serializable data class Person(val name: String, val age: Int) class MyFragment : Fragment() { val person by saved { Person("John Doe", 21) } }
73. @Serializable data class Person(val name: String, val age: Int) val navController = rememberNavController() NavHost(navController, startDestination = Profile) { composable<Profile> { entry: NavBackStackEntry -> val selectedUser by remember { entry.saved { Person("John Doe", 21) } } Profile(navController) } }
74. @Serializable data class Person(val name: String, val age: Int) val backStack = rememberNavBackStack() NavDisplay(backStack, entryProvider = entryProvider { entry<Profile> { val owner = LocalSavedStateRegistryOwner.current.savedStateRegistry val selectedUser by remember { owner.saved { Person("John Doe", 21) } } Profile(navController) } )
75. KotlinX Serialization + Compose
76. @Serializable data class Person(val name: String, val age: Int) @Composable fun MyComposable() { val saveable = rememberSaveable(serializer = serializer<Person>()) { Person("John Doe", 21) } }
77. @Serializable data class Person(val name: String, val age: Int) @Composable fun MyComposable() { val saveable = rememberSaveable(serializer = serializer<Person>()) { Person("John Doe", 21) } }
78. @Serializable data class Person(val name: String, val age: Int) val backStack = rememberNavBackStack() NavDisplay(backStack, entryProvider = entryProvider { entry<Profile> { val owner = LocalSavedStateRegistryOwner.current val registry = owner.savedStateRegistry val person by remember { registry.saved { Person("John Doe", 21) } } Profile(person) } )
79. @Serializable data class Person(val name: String, val age: Int) val backStack = rememberNavBackStack() NavDisplay(backStack, entryProvider = entryProvider { entry<Profile> { val person by rememberSaveable(serializer = serializer<Person>()) { Person("John Doe", 21) } Profile(person) } )
80. Proprietary + Confidential 03 Creating a new library for KMP
81. What is Navigation Event?
82. • System Back ◦ Predictive Back What is Navigation Event?
83. • System Back ◦ Predictive Back • Keyboard Events What is Navigation Event? • System Back ◦ Predictive Back
84. • System Back ◦ Predictive Back • Keyboard Events • Forward Navigation What is Navigation Event? • System Back ◦ Predictive Back • Keyboard Events
85. OnBackPressedDispatcher
86. OnBackPressedDispatcher • Added in the AndroidX Activity 1.0.0 release
87. OnBackPressedDispatcher • Added in the AndroidX Activity 1.0.0 release • Available from ComponentActivity • Added in the AndroidX Activity 1.0.0 release
88. OnBackPressedDispatcher • Added in the AndroidX Activity 1.0.0 release • Available from ComponentActivity • Register OnBackPressedCallback to listen for events • Added in the AndroidX Activity 1.0.0 release • Available from ComponentActivity
89. OnBackPressedDispatcher • Added in the AndroidX Activity 1.0.0 release • Available from ComponentActivity • Register OnBackPressedCallback to listen for events • Predictive/BackHandler in Compose • Added in the AndroidX Activity 1.0.0 release • Available from ComponentActivity • Register OnBackPressedCallback to listen for events
90. class MyComponent(activity: ComponentActivity) { val dispatcher = activity.onBackPressedDispatcher init { dispatcher.addCallback(object : OnBackPressedCallback(true) { override fun handleOnBackStarted(backEvent: BackEventCompat) {...} override fun handleOnBackProgressed(backEvent: BackEventCompat) {...} override fun handleOnBackPressed() {...} override fun handleOnBackCancelled() {...} }) } } OnBackPressedDispatcher
91. class MyComponent(activity: ComponentActivity) { val dispatcher = activity.onBackPressedDispatcher init { dispatcher.addCallback(object : OnBackPressedCallback(true) { override fun handleOnBackStarted(backEvent: BackEventCompat) {...} override fun handleOnBackProgressed(backEvent: BackEventCompat) {...} override fun handleOnBackPressed() {...} override fun handleOnBackCancelled() {...} }) } } OnBackPressedDispatcher
92. class MyComponent(activity: ComponentActivity) { val dispatcher = activity.onBackPressedDispatcher init { dispatcher.addCallback(object : OnBackPressedCallback(true) { override fun handleOnBackStarted(backEvent: BackEventCompat) {...} override fun handleOnBackProgressed(backEvent: BackEventCompat) {...} override fun handleOnBackPressed() {...} override fun handleOnBackCancelled() {...} }) } } OnBackPressedDispatcher
93. class MyComponent(activity: ComponentActivity) { val dispatcher = activity.onBackPressedDispatcher init { dispatcher.addCallback(object : OnBackPressedCallback(true) { override fun handleOnBackStarted(backEvent: BackEventCompat) {...} override fun handleOnBackProgressed(backEvent: BackEventCompat) {...} override fun handleOnBackPressed() {...} override fun handleOnBackCancelled() {...} }) } } OnBackPressedDispatcher
94. class MyComponent(activity: ComponentActivity) { val dispatcher = activity.onBackPressedDispatcher init { dispatcher.addCallback(object : OnBackPressedCallback(true) { override fun handleOnBackStarted(backEvent: BackEventCompat) {...} override fun handleOnBackProgressed(backEvent: BackEventCompat) {...} override fun handleOnBackPressed() {...} override fun handleOnBackCancelled() {...} }) } } OnBackPressedDispatcher
95. class MyComponent(activity: ComponentActivity) { val dispatcher = activity.onBackPressedDispatcher init { dispatcher.addCallback(object : OnBackPressedCallback(true) { override fun handleOnBackStarted(backEvent: BackEventCompat) {...} override fun handleOnBackProgressed(backEvent: BackEventCompat) {...} override fun handleOnBackPressed() {...} override fun handleOnBackCancelled() {...} }) } } OnBackPressedDispatcher
96. class MyComponent(activity: ComponentActivity) { val dispatcher = activity.onBackPressedDispatcher init { dispatcher.addCallback(object : OnBackPressedCallback(true) { override fun handleOnBackStarted(backEvent: BackEventCompat) {...} override fun handleOnBackProgressed(backEvent: BackEventCompat) {...} override fun handleOnBackPressed() {...} override fun handleOnBackCancelled() {...} }) } } OnBackPressedDispatcher
97. class MyComponent(activity: ComponentActivity) { val dispatcher = activity.onBackPressedDispatcher init { dispatcher.addCallback { /* handle system back here */ } } } OnBackPressedDispatcher
98. class MyComponent(activity: ComponentActivity) { val dispatcher = activity.onBackPressedDispatcher init { dispatcher.addCallback { /* handle system back here */ } } } OnBackPressedDispatcher
99. @Composable fun myComposable() { PredictiveBackHandler(true /* enabled condition */) { backEvent -> /* handleOnBackStarted */ try { backEvent.collect { /* handleOnBackProgressed */} /* handleOnBackPressed */ } finally { /* handleOnBackCancelled */ } } } PredictiveBackHandler
100. @Composable fun myComposable() { PredictiveBackHandler(true /* enabled condition */) { backEvent -> /* handleOnBackStarted */ try { backEvent.collect { /* handleOnBackProgressed */} /* handleOnBackPressed */ } finally { /* handleOnBackCancelled */ } } } PredictiveBackHandler
101. @Composable fun myComposable() { PredictiveBackHandler(true /* enabled condition */) { backEvent -> /* handleOnBackStarted */ try { backEvent.collect { /* handleOnBackProgressed */} /* handleOnBackPressed */ } finally { /* handleOnBackCancelled */ } } } PredictiveBackHandler
102. @Composable fun myComposable() { PredictiveBackHandler(true /* enabled condition */) { backEvent -> /* handleOnBackStarted */ try { backEvent.collect { /* handleOnBackProgressed */} /* handleOnBackPressed */ } finally { /* handleOnBackCancelled */ } } } PredictiveBackHandler
103. @Composable fun myComposable() { PredictiveBackHandler(true /* enabled condition */) { backEvent -> /* handleOnBackStarted */ try { backEvent.collect { /* handleOnBackProgressed */} /* handleOnBackPressed */ } finally { /* handleOnBackCancelled */ } } } PredictiveBackHandler
104. @Composable fun myComposable() { PredictiveBackHandler(true /* enabled condition */) { backEvent -> /* handleOnBackStarted */ try { backEvent.collect { /* handleOnBackProgressed */} /* handleOnBackPressed */ } finally { /* handleOnBackCancelled */ } } } PredictiveBackHandler
105. @Composable fun myComposable() { PredictiveBackHandler(true /* enabled condition */) { backEvent -> /* handleOnBackStarted */ try { backEvent.collect { /* handleOnBackProgressed */} /* handleOnBackPressed */ } finally { /* handleOnBackCancelled */ } } } PredictiveBackHandler
106. @Composable fun myComposable() { PredictiveBackHandler(true /* enabled condition */) { backEvent -> /* handleOnBackStarted */ try { backEvent.collect { /* handleOnBackProgressed */} /* handleOnBackPressed */ } finally { /* handleOnBackCancelled */ } } } PredictiveBackHandler
107. @Composable fun myComposable() { PredictiveBackHandler(true /* enabled condition */) { backEvent -> /* handleOnBackStarted */ try { backEvent.collect { /* handleOnBackProgressed */} /* handleOnBackPressed */ } finally { /* handleOnBackCancelled */ } } } PredictiveBackHandler
108. Brief Vocabulary
109. System Back Trio onBackPressedCallback onBackInvokedCallback NavigationEventCallback OnBackPressedDispatcher OnBackInvokedDispatcher NavigationEventDispatcher Platform AndroidX AndroidX
110. OnBackPressedDispatcher
111. OnBackPressedDispatcher
112. OnBackPressedDispatcher
113. OnBackPressedDispatcher
114. OnBackPressedDispatcher
115. OnBackPressedDispatcher
116. OnBackPressedDispatcher
117. Back Up Forward Home Android Phone ✅ ✅ ❓ ✅ Android Tablet ✅ ✅ ❓ ✅ Android XR ✅ ✅ ❓ ✅ Web (Browser) ✅ ✅ ✅ ❓ iOS ✅ ❓ ❓ ✅ Desktop (Multiplatform) ✅ ❓ ❓ ❓ System Events on other Platforms
118. Navigation Event
119. Navigation Event
120. Navigation Event
121. Expect Actual
122. public expect class NavigationInputHandler { private val dispatcher: NavigationEventDispatcher internal fun updateActiveState() } public expect class NavigationEvent { public constructor( touchX: Float, touchY: Float, progress: Float, swipeEdge: @SwipeEdge Int, frameTimeMillis: Long = 0 ) } Expect Classes
123. public expect class NavigationInputHandler { private val dispatcher: NavigationEventDispatcher internal fun updateActiveState() } public expect class NavigationEvent { public constructor( touchX: Float, touchY: Float, progress: Float, swipeEdge: @SwipeEdge Int, frameTimeMillis: Long = 0 ) } Expect Classes
124. public expect class NavigationInputHandler { private val dispatcher: NavigationEventDispatcher internal fun updateActiveState() } public expect class NavigationEvent { public constructor( touchX: Float, touchY: Float, progress: Float, swipeEdge: @SwipeEdge Int, frameTimeMillis: Long = 0 ) } Expect Classes
125. public expect class NavigationInputHandler { private val dispatcher: NavigationEventDispatcher internal fun updateActiveState() } public expect class NavigationEvent { public constructor( touchX: Float, touchY: Float, progress: Float, swipeEdge: @SwipeEdge Int, frameTimeMillis: Long = 0 ) } Expect Classes
126. public expect class NavigationInputHandler { private val dispatcher: NavigationEventDispatcher internal fun updateActiveState() } public expect class NavigationEvent { public constructor( touchX: Float, touchY: Float, progress: Float, swipeEdge: @SwipeEdge Int, frameTimeMillis: Long = 0 ) } Expect Classes
127. public expect class NavigationInputHandler { private val dispatcher: NavigationEventDispatcher internal fun updateActiveState() } public expect class NavigationEvent { public constructor( touchX: Float, touchY: Float, progress: Float, swipeEdge: @SwipeEdge Int, frameTimeMillis: Long = 0 ) } Expect Classes
128. public expect class NavigationInputHandler { private val dispatcher: NavigationEventDispatcher internal fun updateActiveState() } public expect class NavigationEvent { public constructor( touchX: Float, touchY: Float, progress: Float, swipeEdge: @SwipeEdge Int, frameTimeMillis: Long = 0 ) } Expect Classes
129. public expect class NavigationInputHandler { private val dispatcher: NavigationEventDispatcher internal fun updateActiveState() } public expect class NavigationEvent { public constructor( touchX: Float, touchY: Float, progress: Float, swipeEdge: @SwipeEdge Int, frameTimeMillis: Long = 0 ) } Expect Classes
130. public expect class NavigationInputHandler { private val dispatcher: NavigationEventDispatcher internal fun updateActiveState() } public expect class NavigationEvent { public constructor( touchX: Float, touchY: Float, progress: Float, swipeEdge: @SwipeEdge Int, frameTimeMillis: Long = 0 ) } Expect Classes
131. Navigation Event
132. Navigation Event
133. Verifying the new approach
134. • Re-write OnBackPressedDispatcher on top of NavigationEvent Verifying the new approach
135. • Re-write OnBackPressedDispatcher on top of NavigationEvent Verifying the new approach
136. • Re-write OnBackPressedDispatcher on top of NavigationEvent • Allow integration with the new Navigation3 library Verifying the new approach • Re-write OnBackPressedDispatcher on top of NavigationEvent
137. OnBackPressed Rewrite
138. OnBackPressed Rewrite
139. OnBackPressed Rewrite
140. OnBackPressed Rewrite
141. OnBackPressed Rewrite
142. OnBackPressed Rewrite
143. OnBackPressed Rewrite
144. OnBackPressed Rewrite
145. public expect class NavigationEvent { public constructor( touchX: Float, touchY: Float, progress: Float, swipeEdge: @SwipeEdge Int, frameTimeMillis: Long = 0 ) } Expect NavigationEvent
146. public actual class NavigationEvent actual constructor(...) { public constructor(backEvent: BackEvent) : this( touchX = backEvent.touchX, touchY = backEvent.touchY, progress = backEvent.progress, swipeEdge = backEvent.swipeEdge, frameTimeMillis = backEvent.frameTimeMillis, ) } Actual NavigationEvent
147. public actual class NavigationEvent actual constructor(...) { public constructor(backEvent: BackEvent) : this( touchX = backEvent.touchX, touchY = backEvent.touchY, progress = backEvent.progress, swipeEdge = backEvent.swipeEdge, frameTimeMillis = backEvent.frameTimeMillis, ) } Actual NavigationEvent
148. public expect class NavigationInputHandler { private val dispatcher: NavigationEventDispatcher internal fun updateActiveState() } Expect NavigationInputHandler
149. public actual class NavigationInputHandler(val dispatcher:...) { private var invoker: OnBackInvokedDispatcher? = null private var onBackInvokedCallback: OnBackInvokedCallback? = null private var registered = false public fun setOnBackInvokedDispatcher(invoker: OnBackInvokedDispatcher) { this.invoker = invoker updateActiveState() } init { ... } internal actual fun updateActiveState() { ... } } Actual NavigationInputHandler
150. public actual class NavigationInputHandler(val dispatcher:...) { private var invoker: OnBackInvokedDispatcher? = null private var onBackInvokedCallback: OnBackInvokedCallback? = null private var registered = false public fun setOnBackInvokedDispatcher(invoker: OnBackInvokedDispatcher) { this.invoker = invoker updateActiveState() } init { ... } internal actual fun updateActiveState() { ... } } Actual NavigationInputHandler
151. public actual class NavigationInputHandler(val dispatcher:...) { private var invoker: OnBackInvokedDispatcher? = null private var onBackInvokedCallback: OnBackInvokedCallback? = null private var registered = false public fun setOnBackInvokedDispatcher(invoker: OnBackInvokedDispatcher) { this.invoker = invoker updateActiveState() } init { ... } internal actual fun updateActiveState() { ... } } Actual NavigationInputHandler
152. public actual class NavigationInputHandler(val dispatcher:...) { private var invoker: OnBackInvokedDispatcher? = null private var onBackInvokedCallback: OnBackInvokedCallback? = null private var registered = false public fun setOnBackInvokedDispatcher(invoker: OnBackInvokedDispatcher) { this.invoker = invoker updateActiveState() } init { ... } internal actual fun updateActiveState() { ... } } Actual NavigationInputHandler
153. public actual class NavigationInputHandler(val dispatcher:...) { private var invoker: OnBackInvokedDispatcher? = null private var onBackInvokedCallback: OnBackInvokedCallback? = null private var registered = false public fun setOnBackInvokedDispatcher(invoker: OnBackInvokedDispatcher) { this.invoker = invoker updateActiveState() } init { ... } internal actual fun updateActiveState() { ... } } Actual NavigationInputHandler
154. public actual class NavigationInputHandler(val dispatcher:...) { private var invoker: OnBackInvokedDispatcher? = null private var onBackInvokedCallback: OnBackInvokedCallback? = null private var registered = false public fun setOnBackInvokedDispatcher(invoker: OnBackInvokedDispatcher) { this.invoker = invoker updateActiveState() } init { ... } internal actual fun updateActiveState() { ... } } Actual NavigationInputHandler
155. public actual class NavigationInputHandler(val dispatcher:...) { private var invoker: OnBackInvokedDispatcher? = null private var onBackInvokedCallback: OnBackInvokedCallback? = null private var registered = false public fun setOnBackInvokedDispatcher(invoker: OnBackInvokedDispatcher) { this.invoker = invoker updateActiveState() } init { ... } internal actual fun updateActiveState() { ... } } Actual NavigationInputHandler
156. public actual class NavigationInputHandler(val dispatcher:...) { private var invoker: OnBackInvokedDispatcher? = null private var onBackInvokedCallback: OnBackInvokedCallback? = null private var registered = false public fun setOnBackInvokedDispatcher(invoker: OnBackInvokedDispatcher) { this.invoker = invoker updateActiveState() } init { ... } internal actual fun updateActiveState() { ... } } Actual NavigationInputHandler
157. internal actual fun updateActiveState() { val shouldBeRegistered = dispatcher.hasEnabledCallbacks()\ if (shouldBeRegistered && !registered) { registerOnBackInvokedCallback(...) } else if (!shouldBeRegistered && registered) { unregisterOnBackInvokedCallback(...) } } Actual NavigationInputHandler
158. internal actual fun updateActiveState() { val shouldBeRegistered = dispatcher.hasEnabledCallbacks() if (shouldBeRegistered && !registered) { registerOnBackInvokedCallback(...) } else if (!shouldBeRegistered && registered) { unregisterOnBackInvokedCallback(...) } } Actual NavigationInputHandler
159. internal actual fun updateActiveState() { val shouldBeRegistered = dispatcher.hasEnabledCallbacks() if (shouldBeRegistered && !registered) { registerOnBackInvokedCallback(...) } else if (!shouldBeRegistered && registered) { unregisterOnBackInvokedCallback(...) } } Actual NavigationInputHandler
160. public actual class NavigationInputHandler(val dispatcher:...) { private var invoker: OnBackInvokedDispatcher? = null private var onBackInvokedCallback: OnBackInvokedCallback? = null private var registered = false public fun setOnBackInvokedDispatcher(invoker: OnBackInvokedDispatcher) { this.invoker = invoker updateActiveState() } init { ... } internal actual fun updateActiveState() { ... } } Actual NavigationInputHandler
161. public class NavigationInputHandler(val dispatcher:...) { private var onBackInvokedCallback: OnBackInvokedCallback? = null init { onBackInvokedCallback: OnBackInvokedCallback = OnBackAnimationCallback { override fun onBackStarted(backEvent: BackEvent) { dispatcher.dispatchOnStarted(NavigationEvent(backEvent)) } override fun onBackProgressed(backEvent: BackEvent) { dispatcher.dispatchOnProgressed(NavigationEvent(backEvent)) } override fun onBackInvoked() { dispatcher.dispatchOnCompleted() } override fun onBackCancelled() { dispatcher.dispatchOnCancelled() } } } } Actual NavigationInputHandler
162. public class NavigationInputHandler(val dispatcher:...) { private var onBackInvokedCallback: OnBackInvokedCallback? = null init { onBackInvokedCallback: OnBackInvokedCallback = OnBackAnimationCallback { override fun onBackStarted(backEvent: BackEvent) { dispatcher.dispatchOnStarted(NavigationEvent(backEvent)) } override fun onBackProgressed(backEvent: BackEvent) { dispatcher.dispatchOnProgressed(NavigationEvent(backEvent)) } override fun onBackInvoked() { dispatcher.dispatchOnCompleted() } override fun onBackCancelled() { dispatcher.dispatchOnCancelled() } } } } Actual NavigationInputHandler
163. public class NavigationInputHandler(val dispatcher:...) { private var onBackInvokedCallback: OnBackInvokedCallback? = null init { onBackInvokedCallback: OnBackInvokedCallback = OnBackAnimationCallback { override fun onBackStarted(backEvent: BackEvent) { dispatcher.dispatchOnStarted(NavigationEvent(backEvent)) } override fun onBackProgressed(backEvent: BackEvent) { dispatcher.dispatchOnProgressed(NavigationEvent(backEvent)) } override fun onBackInvoked() { dispatcher.dispatchOnCompleted() } override fun onBackCancelled() { dispatcher.dispatchOnCancelled() } } } } Actual NavigationInputHandler
164. abstract class OnBackPressedCallback(enabled: Boolean) { internal val eventCallback = object : NavigationEventCallback(isEnabled = enabled) { override fun onEventStarted(event: NavigationEvent) { handleOnBackStarted(BackEventCompat(event)) } override fun onEventProgressed(event: NavigationEvent) { handleOnBackProgressed(BackEventCompat(event)) } ... } } OnBackPressedCallback
165. abstract class OnBackPressedCallback(enabled: Boolean) { internal val eventCallback = object : NavigationEventCallback(isEnabled = enabled) { override fun onEventStarted(event: NavigationEvent) { handleOnBackStarted(BackEventCompat(event)) } override fun onEventProgressed(event: NavigationEvent) { handleOnBackProgressed(BackEventCompat(event)) } ... } } OnBackPressedCallback
166. class OnBackPressedDispatcher(...) { fun addCallback(onBackPressedCallback: OnBackPressedCallback) { eventDispatcher.addCallback(onBackPressedCallback.eventCallback) } private fun onBackStarted(backEvent: BackEventCompat) { eventDispatcher.dispatchOnStarted(backEvent.toNavigationEvent()) } private fun onBackProgressed(backEvent: BackEventCompat) { eventDispatcher.dispatchOnProgressed(backEvent.toNavigationEvent()) } ... } OnBackPressedDispatcher
167. class OnBackPressedDispatcher(...) { fun addCallback(onBackPressedCallback: OnBackPressedCallback) { eventDispatcher.addCallback(onBackPressedCallback.eventCallback) } private fun onBackStarted(backEvent: BackEventCompat) { eventDispatcher.dispatchOnStarted(backEvent.toNavigationEvent()) } private fun onBackProgressed(backEvent: BackEventCompat) { eventDispatcher.dispatchOnProgressed(backEvent.toNavigationEvent()) } ... } OnBackPressedDispatcher
168. class OnBackPressedDispatcher(...) { fun addCallback(onBackPressedCallback: OnBackPressedCallback) { eventDispatcher.addCallback(onBackPressedCallback.eventCallback) } private fun onBackStarted(backEvent: BackEventCompat) { eventDispatcher.dispatchOnStarted(backEvent.toNavigationEvent()) } private fun onBackProgressed(backEvent: BackEventCompat) { eventDispatcher.dispatchOnProgressed(backEvent.toNavigationEvent()) } ... } OnBackPressedDispatcher
169. class OnBackPressedDispatcher(...) { fun addCallback(onBackPressedCallback: OnBackPressedCallback) { eventDispatcher.addCallback(onBackPressedCallback.eventCallback) } private fun onBackStarted(backEvent: BackEventCompat) { eventDispatcher.dispatchOnStarted(backEvent.toNavigationEvent()) } private fun onBackProgressed(backEvent: BackEventCompat) { eventDispatcher.dispatchOnProgressed(backEvent.toNavigationEvent()) } ... } OnBackPressedDispatcher
170. class OnBackPressedDispatcher(...) { fun addCallback( owner: LifecycleOwner, onBackPressedCallback: OnBackPressedCallback ) { ... } ... } OnBackPressedDispatcher
171. Navigation 3 Integration
172. Navigation 3 Integration
173. Navigation 3 Integration
174. Navigation 3 Integration
175. What’s next for Navigation Event?
176. • System Back ◦ Predictive Back What’s next for Navigation Event?
177. • System Back ◦ Predictive Back • Keyboard Events What’s next for Navigation Event? • System Back ◦ Predictive Back
178. • System Back ◦ Predictive Back • Keyboard Events • Forward Navigation What’s next for Navigation Event? • System Back ◦ Predictive Back • Keyboard Events
179. Proprietary + Confidential 04 Review
181. ✅ Keeps existing behavior and code that’s already tested. ✅ Can move to KMP step-by-step, reducing risk. ✅ Customers don't need to change their code. ❌ Harder to clean up old or platform-specific design. ❌ May involve complex refactoring and workarounds. Migrate a Library
182. ✅ Keeps existing behavior and code that’s already tested. ✅ Can move to KMP step-by-step, reducing risk. ✅ Customers don't need to change their code. ❌ Harder to clean up old or platform-specific design. ❌ May involve complex refactoring and workarounds. Migrate a Library ✅ Clean design from the start, no legacy "platform-specific" code. ✅ Easier to apply modern best practices. ❌ Slower to build feature parity if the existing library is large. ❌ May miss edge cases already handled in the existing code. ❌ Customers will need to migrate. Rewrite a Library
183. ✅ Keeps existing behavior and code that’s already tested. ✅ Can move to KMP step-by-step, reducing risk. ✅ Customers don't need to change their code. ❌ Harder to clean up old or platform-specific design. ❌ May involve complex refactoring and workarounds. Migrate a Library ✅ Clean design from the start, no legacy "platform-specific" code. ✅ Easier to apply modern best practices. ❌ Slower to build feature parity if the existing library is large. ❌ May miss edge cases already handled in the existing code. ❌ Customers will need to migrate. Rewrite a Library
184. • SavedState 1.3 (KMP + Serialization) • NavigationEvent Alpha01 • Navigation3 Alpha01 New Releases! goo.gle/nav3
185. Thank You, and Donʼt Forget to Vote linkedIn@jeremybwoods 🦋 @marcellogalhardo.dev
186. if (action == Action.Back) { val event = NavigationEvent(currentX, currentY, calculateProgress(startX, currentX, windowSize.width.toFloat()), Edge.Left) backChannel.onProgressed(event) } override fun dispatchEvent(e: NavigationEventWrapper, callback: NavigationEventCallback) { when (e.action) { Action.Back -> { when (e.type) { EventType.Started -> { backNavigation?.let { it.callback.onBackCancelled() } backNavigation = Navigation(callback.deepCopy()).also { it.callback.onBackStarted(e.externalEvent!!) } } EventType.Progressed -> backNavigation?.callback?.onBackProgressed(e.externalEvent!!) EventType.Cancelled -> { backNavigation?.callback?.onBackCancelled() backNavigation = null } EventType.Completed -> { backNavigation?.callback?.onBackCompleted() backNavigation = null } } } } }