Android Weekly Notes #462

2021-06-14 本文已影响0人圣骑士wind

Android Weekly Issue #462

How to parse JSON in Android using Kotlin

原来不用第三方库解析JSON也挺容易的, 就用JSONTokener就行.

Android Vitals - Tap Response Time

Py对点击响应时间的研究.

Handling back presses in Jetpack Compose

关于Compose如何处理back.

首先介绍了导航库的基本实现.

一个简单的单向数据流:

abstract class DetailViewModel : ViewModel() {
    abstract val state: StateFlow<DetailState>
    abstract fun onAction(action: Action)
}

如果我们想获取back的action来进行处理呢?

如果是覆写Activity.onBackPressed()可能会有点丑. 不是很推荐, 见官方文档.

Compose有这么一个BackHandler composable (added in Activity Compose in 1.3.0-alpha02):
源码是这样:

@Composable
public fun BackHandler(enabled: Boolean = true, onBack: () -> Unit) {
    // Safely update the current `onBack` lambda when a new one is provided
    val currentOnBack by rememberUpdatedState(onBack)
    // Remember in Composition a back callback that calls the `onBack` lambda
    val backCallback = remember {
        object : OnBackPressedCallback(enabled) {
            override fun handleOnBackPressed() {
                currentOnBack()
            }
        }
    }
    // On every successful composition, update the callback with the `enabled` value
    SideEffect {
        backCallback.isEnabled = enabled
    }
    val backDispatcher = checkNotNull(LocalOnBackPressedDispatcherOwner.current) {
        "No OnBackPressedDispatcherOwner was provided via LocalOnBackPressedDispatcherOwner"
    }.onBackPressedDispatcher
    val lifecycleOwner = LocalLifecycleOwner.current
    DisposableEffect(lifecycleOwner, backDispatcher) {
        // Add callback to the backDispatcher
        backDispatcher.addCallback(lifecycleOwner, backCallback)
        // When the effect leaves the Composition, remove the callback
        onDispose {
            backCallback.remove()
        }
    }
}

具体使用就很简单了:

@Composable
fun Detail(
    state: DetailState,
    onBack: () -> Unit,
) {
    BackHandler(onBack = onBack)
    Scaffold(
        topBar = { DetailTopAppBar(onBack) }
    ) {
        // detail content
    }
}