如何解决Jetpack撰写：管理共享的UI状态
typealias Actions = @Composable () -> Unit
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContent {
SampleAppTheme {
var currentScreen by remember { mutableStateOf(Screen.A) }
var title by remember { mutableStateOf("Screen A") }
var action by remember { mutableStateOf<Actions>({}) }
Scaffold(
topBar = {
TopAppBar(
title = {
Text(title)
},actions = {
action()
}
)
}
) {
Crossfade(current = currentScreen) { screen ->
when (screen) {
Screen.A -> {
MyScreen(
name = "A",buttonName = "to Screen B",onNext = {
currentScreen = Screen.B
title = "Screen B"
action = {
IconButton(onClick = {}) {
Icon(asset = Icons.Sharp.Home)
}
}
}
)
}
Screen.B -> {
MyScreen(
name = "B",buttonName = "to Screen C",onNext = {
currentScreen = Screen.C
title = "Screen B"
action = {
IconButton(onClick = {}) {
Icon(asset = Icons.Sharp.Close)
}
}
}
)
}
Screen.C -> {
MyScreen(
name = "C",buttonName = "to Screen A",onNext = {
currentScreen = Screen.A
title = "Screen A"
action = {}
}
)
}
}
}
}
}
}
}
}
enum class Screen {
A,B,C
}
@Composable
fun MyScreen(
name: String,buttonName: String,onNext: () -> Unit,) {
Column(
Modifier.fillMaxSize().padding(24.dp),) {
Text(
modifier = Modifier.weight(1f),text = "I am in screen $name!",textAlign = TextAlign.Center,style = MaterialTheme.typography.h3
)
Button(
modifier = Modifier.fillMaxWidth(),onClick = onNext
) {
Text(text = buttonName)
}
}
}
因此，使用此代码，我将看到以下屏幕：
请注意，通过执行以下操作，可以根据当前屏幕更改Actions中的TopAppBar：
MyScreen(
name = "B",onNext = {
currentScreen = Screen.C
title = "Screen B"
// This right here!!!! -------------------
action = {
IconButton(onClick = {}) {
Icon(asset = Icons.Sharp.Close)
}
}
// This right here!!!! -------------------
}
)
Screen.B -> {
// This right here!!!! -------------------
onActive {
title = "Screen B"
action = {
IconButton(onClick = {}) {
Icon(asset = Icons.Sharp.Home)
}
}
}
// This right here!!!! -------------------
MyScreen(
name = "B",onNext = {
currentScreen = Screen.C
}
)
}所以现在，设置状态的责任在当前屏幕上，而不是以前的屏幕上。
这样好吗？
经过一些测试：显然是从屏幕A->屏幕B->屏幕C转移到onActive { }被称为错误的顺序。因此，在某些状态下，屏幕B以屏幕A为标题...屏幕C以屏幕B为标题，依此类推...
即使意识到第一种方法也有缺陷，因为您还必须在返回屏幕时设置状态。.让我们说一下...屏幕A->屏幕B->屏幕C->按下（屏幕B）...现在状态错了...
解决方法
我想这个问题可以使用 Jetpack Navigation for Compose 来解决。
https://developer.android.com/jetpack/compose/navigation
也许这篇文章能帮到你...
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