Android Weekly Issue #476

Tricky refactoring of Jetpack Compose code — be careful with side effects

输入框和snackbar的一个例子.

抽了一个方法之后, 结果就不对了.

最后最好的解决方案是这样:

@Composable
fun LaunchedEffectWrapper(state: SnackbarHostState, text: String) {
    val mostRecentText = rememberUpdatedState(text) // Wrap text
    LaunchedEffect(Unit) {
        ...
        // Use mostRecentText instead of the text
    }
}

其中rememberUpdatedState的实现是:

val state = remember { mutableStateOf(newValue) }
state.value = newState

Guidelines for writing better tests

可读性: 可以适当重复.
Arrange-Act-Assert.
Test a single behavior.
外部依赖.

Optimizing Your Kotlin Build

优化Kotlin build.

Beyond preferences

老的preferences api已经过时了, 现在我们要切换到Jetpack Datastore.

Using Exoplayer in LazyColumn

在一个List里播放Video.

技术方案: ExoPlayer + Compose.

其中针对生命周期的清理部分是这样做的:

val lifecycleOwner by rememberUpdatedState(LocalLifecycleOwner.current)
    DisposableEffect(lifecycleOwner) {
        val lifecycle = lifecycleOwner.lifecycle
        val observer = LifecycleEventObserver { _, event ->
            when (event) {
                Lifecycle.Event.ON_PAUSE -> {
                    exoPlayer.playWhenReady = false
                }
                Lifecycle.Event.ON_RESUME -> {
                    exoPlayer.playWhenReady = true
                }
                Lifecycle.Event.ON_DESTROY -> {
                    exoPlayer.run {
                        stop()
                        release()
                    }
                }
            }
        }
        lifecycle.addObserver(observer)
        onDispose {
            lifecycle.removeObserver(observer)
        }
    }

How much QA is too much QA?

这里头有个插图网站好搞笑: https://www.monkeyuser.com/2018/the-struggle/

Lifecycle-Aware Components Using Android Jetpack

用的是这个api: https://spoonacular.com/food-api/console#Dashboard
得注册, 有apiKey.

Lifecycle Observer

要观察Lifecycle, 实现接口LifecycleObserver:

class NetworkMonitor @Inject constructor(private val context: Context) : LifecycleObserver {
 // Code to observe changes in the network connection.
}

Lifecycle类有两个枚举:

Event: 对应生命周期事件.
State: Lifecycle owner现在的状态.

Lifecycle Owner

谁是LifecycleOwner? -> 实现了LifecycleOwner的类.

Android提供了: ComponentActivity, Fragment.
如果要响应应用的生命周期变化, 用ProcessLifecycleOwner.

创建自定义的Lifecycle Owner

@Singleton
class UnavailableConnectionLifecycleOwner @Inject constructor() : LifecycleOwner {

    private val lifecycleRegistry: LifecycleRegistry = LifecycleRegistry(this)
    
    override fun getLifecycle() = lifecycleRegistry
    
    fun onConnectionLost() {
      lifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_START)
    }
    
    fun onConnectionAvailable() {
      lifecycleRegistry.handleLifecycleEvent(Lifecycle.Event.ON_STOP)
    }
    
    fun addObserver(lifecycleObserver: LifecycleObserver) {
      lifecycleRegistry.addObserver(lifecycleObserver)
    }

}

后面还有关于lifecycle的测试以及LiveData的例子.