android - 在 JetPack Composable 中观察 LiveData

Question

我正在使用宠物应用程序练习 JetPack Compose，并尝试通过 LiveData 观察启动屏幕中的加载状态。但是，在我的可组合项中，我被要求提供 viewLifecycleOwner ，这在可组合项中似乎是不可能的。或者我需要将它从 MainActivity 传递下来吗？看起来很笨重，还有其他更 Jetpacky 的方式吗？

@Composable
fun SplashScreen(navController: NavHostController, isLoadingInit: LiveData<Boolean>) {
    val scale = remember {
        Animatable(0f)
    }
    
    LaunchedEffect(key1 = true) {
        scale.animateTo(
            targetValue = 0.5f,
            animationSpec = tween(
                durationMillis = 500,
                easing = {
                    OvershootInterpolator(2f).getInterpolation(it)
                }
            )
        )
    }

    Box(contentAlignment = Alignment.Center, modifier = Modifier.fillMaxSize()) {
        Image(
            painter = painterResource(id = R.drawable.pokeball),
            contentDescription = "Pokemon Splashscreen",
            modifier = Modifier.scale(scale.value)
        )
    }

    isLoadingInit.observe(**viewLifecycleOwner**) {
        navController.navigate("main-screen")
    }
}

Answer 1

您可以使用 LiveData.observeAsState() 扩展函数将 LiveData 转换为 State。另外，不要将 LiveData 作为参数传递来进行组合，而是先将其转换为 State，然后将其作为参数传递。

// This is probably what you are doing right now (inside a NavGraph)
val isLoadingInit = viewModel.isLoadingInit
SplashScreen(navController, isLoadingInit)

将其更改为:

val isLoadingInit by viewModel.isLoadingInit.observeAsState()
SplashScreen(navController, isLoadingInit)

然后，

@Composable
fun SplashScreen(navController: NavHostController, isLoadingInit: Boolean) {
    LaunchedEffect(isLoadingInit) {
        if(!isLoadingInit) // Or maybe its negation
            navController.navigate("main-screen")
    }
    ...
}