Android Weekly Issue #474

Navigation in multi module Android Compose UI project + Hilt

多module项目的compose导航.

在这个项目中有具体实践:
https://github.com/FunkyMuse/Aurora

Compose architecture: MVVM or MVI with Flow?

Compose声明式, MVVM结合MVI.

• State: 定义composable要绘制的screen.
• Event: 用户action.
• Effect: 只被UI消费一次的action.

sample在这里:
https://github.com/catalinghita8/android-compose-mvvm-foodies

NavigationRailView

NavigationRailView是一个material的导航组件.

Using StateFlow over LiveData for end-to-end operations

使用FLow的例子挺好的.

因为flow是hot的, 所以收集的时候要这样:

lifecycleScope.launch {
    viewModel.mainStateFlow
        .flowWithLifecycle(lifecycle, Lifecycle.State.STARTED)
        .collect { state ->
            if (state is PupImageState.Success) {
                showImage(state.imageUrl)
            } else if (state is PupImageState.Error){
                binding.textViewErrorText.text = state.exception.message
            }
            binding.imageViewPupPicture.isVisible = state is PupImageState.Success
            binding.progressBarLoading.isVisible = state is PupImageState.InProgress
            binding.textViewErrorText.isVisible = state is PupImageState.Error
        }
}

Multimedia Operations for Android using FFmpeg

• https://github.com/SimformSolutionsPvtLtd/SSffmpegVideoOperation

Instagram-like particles animation using Jetpack Compose

用Jetpack Compose做的粒子动画.

Reactive Streams on Kotlin: SharedFlow and StateFlow

SharedFlow:

• hot: 没有人collect也会发射.
• 可以有多个订阅者.
• 永远不会complete.

代码:

private val _sharedViewEffects = MutableSharedFlow<SharedViewEffects>() // 1

val sharedViewEffects = _sharedViewEffects.asSharedFlow() // 2

发射元素有两个方法:

• emit: suspend方法.
• tryEmit: 非suspend方法.

SharedFLow的buffer是干啥的?

如果subscriber suspend了, sharedflow会suspend这个steam, buffer这个要发射的元素, 等待subscriber resume.

Because onBufferOverflow is set with BufferOverflow.SUSPEND, the flow will suspend until it can deliver the event to all subscribers.

total buffer是: replay + extraBufferCapacity.

在UI里subscribe的时候:

viewLifecycleOwner.lifecycleScope.launchWhenStarted { // 1
  sharedViewModel.sharedViewEffects.collect { // 2
    when (it) {
      // 3
      is SharedViewEffects.PriceVariation -> notifyOfPriceVariation(it.variation)
    }
  }
}

SharedFlow是用来取代BroadcastChannel的.

StateFlow

StateFlow是特质版的SharedFlow.

可以这样创建一个有StateFlow行为的SharedFlow:

val shared = MutableSharedFlow(
    replay = 1,
    onBufferOverflow = BufferOverflow.DROP_OLDEST
)
shared.tryEmit(InitialState()) // emit the initial value
val state = shared.distinctUntilChanged() // get StateFlow-like behavior

如果是StateFlow, 就不要用emit和tryEmit了.

应该用:

mutableState.value = newState

注意它的conflated特性, 赋值的时候要用不可变的值.

订阅的时候也是:

private fun observeViewStateUpdates(adapter: CoinAdapter) {
  viewLifecycleOwner.lifecycleScope.launchWhenStarted {
    viewModel.viewState.collect { updateUi(it, adapter) }
  }
}

StateFlow可以取代ConflatedBroadcastChannel.

RxJava的等价替代:

• PublishSubject -> SharedFlow.
• BehaviorSubject -> StateFlow.

一次性事件:
https://proandroiddev.com/android-singleliveevent-redux-with-kotlin-flow-b755c70bb055
这里面的这个工具类还挺好的:

class FlowObserver<T> (
    lifecycleOwner: LifecycleOwner,
    private val flow: Flow<T>,
    private val collector: suspend (T) -> Unit
) {

    private var job: Job? = null

    init {
        lifecycleOwner.lifecycle.addObserver(LifecycleEventObserver {
                source: LifecycleOwner, event: Lifecycle.Event ->
            when (event) {
                Lifecycle.Event.ON_START -> {
                    job = source.lifecycleScope.launch {
                        flow.collect { collector(it) }
                    }
                }
                Lifecycle.Event.ON_STOP -> {
                    job?.cancel()
                    job = null
                }
                else -> { }
            }
        })
    }
}


inline fun <reified T> Flow<T>.observeOnLifecycle(
    lifecycleOwner: LifecycleOwner,
    noinline collector: suspend (T) -> Unit
) = FlowObserver(lifecycleOwner, this, collector)

inline fun <reified T> Flow<T>.observeInLifecycle(
    lifecycleOwner: LifecycleOwner
) = FlowObserver(lifecycleOwner, this, {})

How To Securely Build and Sign Your Android App With GitHub Actions

在GitHub Action的Workflow上如何配置签名.

Kotlin flow: Nesting vs Chaining

流的两种模式:

链式:

stream1
    .flatMap { stream2 }
    .flatMap { stream3 }
    .flatMap { stream4 }
    .collect()

嵌套式:

stream1
    .flatMap {
        stream2.flatMap {
            stream3.flatMap {
                stream4
            }
        }
    }
    .collect()

有一些情形适合嵌套:

• 在流之间传递数据. 比如用一个api返回的结果作为参数请求另一个api, 而且有共同需要的参数.

比如

observeUser()
    .flatMap { user ->
        api.load(user.id)
            .flatMap { data -> api.send(user.id, data) }
    }
    .collect()

如果不用嵌套式, 那么第二个请求没法获取user参数.

• 处理scope lifecycle.

observeUser()
    .flatMapLatest { user -> 
        api.load(user.id)
            .flatMapLatest { observeLocation() }
    }
    .collect()

Compose: UI Screenshot Testing

Compose的UI screenshot testing.

这里有个重要的ScreenshotComparator.kt

Code

• 一个变形动画的layout: https://github.com/skydoves/transformationlayout
• 一个创建compose app的工具: https://github.com/theapache64/create-compose-app android版本的template: https://github.com/theapache64/compose-android-template
• https://github.com/microsoft/surface-duo-window-manager-samples
• https://github.com/akshay2211/BubbleTabBar
• https://github.com/MackHartley/DashedView