Jetpack撰写：管理共享的UI状态

Question

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",
    buttonName = "to Screen C",
    onNext = {
        currentScreen = Screen.C
        title = "Screen B"
        // This right here!!!! -------------------
        action = { 
            IconButton(onClick = {}) {
                Icon(asset = Icons.Sharp.Close)
            }
        }
        // This right here!!!! -------------------
    }
)

1. 我的第一个问题是这是否是正确的方法？

2. 对于第二个问题，我觉得我在上一个屏幕中设置的值应该由当前屏幕负责。所以我尝试这样做？

Screen.B -> {
    // This right here!!!! -------------------
    onActive {
         title = "Screen B"
         action = { 
             IconButton(onClick = {}) {
                 Icon(asset = Icons.Sharp.Home)
             }
         }
    }
    // This right here!!!! -------------------
    MyScreen(
         name = "B",
         buttonName = "to Screen C",
         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...

Answer 1

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...

https://afzaln.com/intro-to-jetpack-compose-navigation/