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Merge branch 'CORE/feat/FCAN-1841_enable-compose-communication' into …
…'main' FCAN-1841 | Feat (CORE) : Enable composables communication See merge request veepee/offerdiscovery/products/front-mobile/android/link-router!24
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changelog/next/CORE_FCAN-1841_enable-compose-communication.md
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| --- | ||
| title: Enable composables communication | ||
| url: https://jira.vptech.eu/browse/FCAN-1841 | ||
| author: Julio Cesar Bueno Cotta | ||
| --- | ||
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| Android components have ways of implicit communication, for instance | ||
| - Activities -> Activities -> OnActivityResult/Contracts | ||
| - Fragments -> Fragments -> Fragment Result API | ||
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| The started activity don't need to know which Activity called it, the Fragments sending results are not required to know who is listening for it's results. | ||
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| But how about Composables -> ??? | ||
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| Compose does not provide an out of the box solution to send implicit events to the callers. | ||
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| ### What did I do? | ||
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| This MR tries to enable that communication in a **somewhat** type safe way. | ||
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| Our approach avoids "lambda forwarding" by using a `LinkRouterEventHandler` that is instantiated when accessing a `LinkRouterEventHandlerContainer`. | ||
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| Example : | ||
| ``` kotlin | ||
| sealed interface MyData : ComposableEvent { | ||
| data class MyData1(val foo: String) : MyData | ||
| data class MyData2(val foo: String) : MyData | ||
| } | ||
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| @Composable | ||
| fun MyScreen() { | ||
| LinkRouterEventHandlerContainer<MyData>(onEvent = { | ||
| println(it) | ||
| }, | ||
| content = { | ||
| MyDataComposable() | ||
| } | ||
| ) | ||
| } | ||
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| @Composable | ||
| private fun MyDataComposable() { | ||
| MySecondLayerDataComposable() | ||
| } | ||
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| @Composable | ||
| private fun MySecondLayerDataComposable() { | ||
| val handler = LocalLinkRouterEventHandler.current | ||
| BasicText( | ||
| "hello world", | ||
| modifier = Modifier.clickable { handler.publish(MyData.MyData1("bar")) }) | ||
| } | ||
| ``` | ||
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| Event though `MySecondLayerDataComposable` is a leaf composable and does not contain a "onClick : () -> Unit" lambda, the onClick event arrives to `onEvent` lambda in `MyScreen` composable. | ||
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| We say that this API is **somewhat** type safe because there is no guarantees that a `LinkRouterEventHandlerContainer` will be listening for the published type. | ||
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| For instance: | ||
| ``` kotlin | ||
| @Composable | ||
| private fun MySecondLayerDataComposable() { | ||
| val handler = LocalLinkRouterEventHandler.current | ||
| BasicText( | ||
| "hello world", | ||
| modifier = Modifier.clickable { handler.publish("foobar") }) | ||
| } | ||
| ``` | ||
| Would cause an error at **runtime** as there is no registered `LinkRouterEventHandlerContainer` that can handle Strings. | ||
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| The new composable `ComposableFor` is meant to be called with `ComposableLinkWithEvent` implementations and offers a lambda with the expected event type that can be emitted | ||
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| ``` kotlin | ||
| ComposableFor( | ||
| link = FeatureBComposableLink("1 - AActivity sent this text to a Composable in B Module"), | ||
| modifier = modifier | ||
| .fillMaxWidth() | ||
| .background(Color.Yellow) | ||
| ) { event -> | ||
| text = event.messageSize.toString() | ||
| } | ||
| ``` | ||
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| The `FeatureBComposableLink` class is defined as | ||
| ``` | ||
| class TestComposableBLink( | ||
| override val parameter: TestComposableBParameter | ||
| ) : ComposableLinkWithEvent<TestComposableName, TestComposableBLinkEvent> { | ||
| override val composableName: TestComposableName = TestComposableName.TestComposableB | ||
| } | ||
| data class TestComposableBParameter(val message: String) : ComposableParameter | ||
| data class TestComposableBLinkEvent(val foo: String) : ComposableEvent | ||
| ``` | ||
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| Notice that it implements `ComposableLinkWithEvent`, not `ComposableLink` as we need the `ComposableEvent` type to ensure the correct match of types when routing this link. | ||
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| ### Notes: | ||
| - Is this fine? With this we open the gate to a new class of bugs in the project, runtime errors due to missing event handlers. | ||
| - Should `ComposableEvent` be renamed to `ComposableResult` ? I don't quite like the `Event` suffix. | ||
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| ### QA: | ||
| 1) what will happen if I call `handler.publish()` with a type that is not directly handled by the nearest EventHandler ? | ||
| The event will be forwarded to the next EventHandler until it reaches an EventHandler that can handle it or the topmost EventHandler where we are raising en exception and crashing. | ||
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| 2) Can I use this to avoid the lambdas inside my feature composables? | ||
| Yes, but be aware that Google does not recommend this! We are using this in LinkRouter because we couldn't find a better way of sharing events in a generic way without rewriting the library. | ||
| As I stated above, there is no compile time check if an EventHandler is deployed in the compose hierarchy that can handle the type you want to publish. | ||
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| 3) Can I use primitive types as Events? | ||
| Yes, but you **really** should think in using a sealed class or sealed interface for your public API as the caller can use a `when` to evaluate all possible states. |
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.../main/java/com/veepee/vpcore/route/link/compose/events/LinkRouterEventHandlerContainer.kt
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| package com.veepee.vpcore.route.link.compose.events | ||
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| import androidx.compose.runtime.Composable | ||
| import androidx.compose.runtime.CompositionLocalProvider | ||
| import androidx.compose.runtime.ProvidableCompositionLocal | ||
| import androidx.compose.runtime.compositionLocalOf | ||
| import com.veepee.vpcore.route.link.compose.ComposableEvent | ||
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| @Composable | ||
| inline fun <reified Event : ComposableEvent> LinkRouterEventHandlerContainer( | ||
| current: LinkRouterEventHandler<out ComposableEvent> = LocalLinkRouterEventHandler.current, | ||
| noinline onEvent: (Event) -> Unit, | ||
| crossinline content: @Composable () -> Unit | ||
| ) { | ||
| CompositionLocalProvider( | ||
| LocalLinkRouterEventHandler provides LinkRouterEventHandler( | ||
| parent = current, | ||
| isAssignableFrom = { event -> | ||
| Event::class.java.isAssignableFrom(event::class.java) | ||
| }, | ||
| onEvent = onEvent | ||
| ) | ||
| ) { | ||
| content() | ||
| } | ||
| } | ||
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| class LinkRouterEventHandler<Event : ComposableEvent> constructor( | ||
| private val parent: LinkRouterEventHandler<out ComposableEvent>? = null, | ||
| private val isAssignableFrom: (event: Any) -> Boolean, | ||
| private val onEvent: (Event) -> Unit | ||
| ) { | ||
| @Suppress("UNCHECKED_CAST") | ||
| fun publish(event: ComposableEvent) { | ||
| if (isAssignableFrom(event)) { | ||
| onEvent(event as Event) | ||
| } else if (parent == null) { | ||
| throw NoParentEventHandlerException() | ||
| } else { | ||
| parent.publish(event) | ||
| } | ||
| } | ||
| } | ||
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| class NoParentEventHandlerException : RuntimeException("No parent LocalEventHandler found!") | ||
| class NoEventHandlerException(event: ComposableEvent) : | ||
| RuntimeException("Your event \"$event\" reached the topmost EventHandler one in the compose hierarchy without a handler!") | ||
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| val LocalLinkRouterEventHandler: ProvidableCompositionLocal<LinkRouterEventHandler<out ComposableEvent>> = | ||
| compositionLocalOf { | ||
| LinkRouterEventHandler( | ||
| isAssignableFrom = { true }, | ||
| onEvent = { event -> | ||
| throw NoEventHandlerException(event) | ||
| } | ||
| ) | ||
| } |
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