如何在创建它的参数发生变化时替换 Android Jetpack Compose AndroidView？

Question

我有一个应用程序可以显示封装在 AndroidView 中的几个不同视图。在下面要重现的简单示例中，这些只是 TextView 个实例。问题是更改文本（在本例中循环显示三个不同的值）似乎不会更新应用程序显示的内容。

sealed class AppView
data class ShowSomeText(val text: String) : AppView()
data class SomeOtherState(val data: Any?) : AppView()
data class ShowSomeText2(val text: String) : AppView()

class AppViewModel : ViewModel() {

    var currentView = MutableLiveData<AppView>(ShowSomeText("original text"))
    var currentViewWorkaround = MutableLiveData<AppView>(ShowSomeText("original text"))


    private val textRing = arrayOf("one", "two", "three")
    private var textRingPosition = 0

    fun incrementTextState() {
        val nextState = ShowSomeText(textRing[textRingPosition])
        currentView.postValue(nextState)

        val nextStateWorkaround = when(currentViewWorkaround.value) {
            is ShowSomeText -> ShowSomeText2(textRing[textRingPosition])
            else -> ShowSomeText(textRing[textRingPosition])
        }
        currentViewWorkaround.postValue(nextStateWorkaround)
        textRingPosition = (textRingPosition + 1) % textRing.size
    }
}

class MainActivity : AppCompatActivity() {

    private val viewModel = AppViewModel()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            ViewContainer(viewModel)
        }
    }
}

@Composable
fun ViewContainer(viewModel: AppViewModel) {

    // Add this to gradle.build for the observeAsState function:
    //     implementation "androidx.compose.runtime:runtime-livedata:$compose_version"
    val currentView: AppView by viewModel.currentView.observeAsState(ShowSomeText("starting text"))
    val currentViewWorkaround: AppView by viewModel.currentViewWorkaround.observeAsState(ShowSomeText("starting text"))

    Column {
        Button(onClick = viewModel::incrementTextState) {
            Text(
                text = "tap to change",
                style = TextStyle(fontSize = 12.em)
            )
        }
        Text("Compose Text")
        when (currentView) {
            is ShowSomeText -> createComposeTextView((currentView as ShowSomeText).text)
            is SomeOtherState -> Text("the other state")
        }
        Text("AndroidView wrapping TextView")
        when (currentView) {
            is ShowSomeText -> createAndroidViewForTextView((currentView as ShowSomeText).text)
            is SomeOtherState -> Text("the other state")
        }
        Text("AndroidView wrapping TextView with 2-state workaround")
        when (currentViewWorkaround) {
            is ShowSomeText -> createAndroidViewForTextView((currentViewWorkaround as ShowSomeText).text)
            is ShowSomeText2 -> createAndroidViewForTextView((currentViewWorkaround as ShowSomeText2).text)
            is SomeOtherState -> Text("the other state")
        }
    }

}

@Composable
fun createAndroidViewForTextView(text: String) {
    val context = ContextAmbient.current
    val tv = remember(text, context) {
        val x = TextView(context)
        x.text = text
        x.textSize = 48.0f
        x
    }
    AndroidView({ tv })
}

@Composable
fun createComposeTextView(text: String) {
    Text(text, style = TextStyle(fontSize = 12.em))
}

第一个文本通过 Compose Text 函数显示并且有效，第二个文本使用 TextView 包装了 AndroidView Compose 函数但不起作用，第三个文本也使用相同的 AndroidView 包装器但通过使用另一种状态以某种方式触发更改变量。

为什么中间的文字没有更新？

使用黑客修复复制 kt 文件的完整要点：https://gist.github.com/okhobb/ba7791af4562ea672d0c52769a7cd8ba

============

更新：基于已接受答案的工作代码：

@Composable
fun TraditionalViewAsComposable(text: String){

    var updatableString by remember{mutableStateOf("")}
    updatableString = text

    AndroidView(
        factory={ TextView(it).apply {
            this.text = text
            this.textSize = 48.0f
        } },
        update={ it.text = updatableString }
    )
}

Answer 1

索引必须是可变状态，例如：textRingPosition = remember{ mutableStateOf<Int>(0) }.

作为一般提示，如果您的 Compose 代码包含 var 可能有问题，应该是一个状态。

说明：如果您运行此代码片段按下按钮，但可组合项未更新，但在控制台中您会看到值已更改。

Surface(modifier = Modifier.padding(all = 16.dp).fillMaxSize()) {
    val textRing = arrayOf("one", "two", "three")
    var textRingPosition = 0
    val liveData = MutableLiveData<String>()
    val observeAsState: String by liveData.observeAsState(initial = textRing[textRingPosition])

    Column() {
        println("Composed with " + observeAsState + " and pos: " + textRingPosition)
        Text("Text: " + observeAsState)
        Button(onClick = {
            textRingPosition = textRingPosition.inc().rem(textRing.size)
            println("OnClick: " + textRingPosition)
            liveData.postValue(textRing[textRingPosition])
        }) {
            Text("change")
        }
    }
}

控制台输出：

1 | I/System.out: Composed with one and pos: 0
2 | I/System.out: OnClick: 1
3 | I/System.out: Composed with two and pos: 0
4 | I/System.out: OnClick: 1
5 | I/System.out: OnClick: 2
6 | I/System.out: Composed with three and pos: 0
7 | I/System.out: OnClick: 1
8 | I/System.out: Composed with two and pos: 0
9 | I/System.out: OnClick: 1

在第 4 行中，您可以看到索引已更改为 1，但它应该已经在 2，这是因为视图在第 3 行中重新组合并重置了索引。 Compose 不会在这里重新组合，因为视图不需要更新，因为当前值与状态中的新值相同。在第 5 行中，索引是 2，它将状态的值更改为另一个字符串，从而触发重组。

有了索引的记忆和可变状态，组件将重新组合每个更改：

Surface(modifier = Modifier.padding(all = 16.dp).fillMaxSize()) {
    val textRing = arrayOf("one", "two", "three")
    var textRingPosition = 0
    val liveData = MutableLiveData<String>()
    val observeAsState: String by liveData.observeAsState(initial = textRing[textRingPosition])

    val rememberTextRingPosition = remember { mutableStateOf(0) }

    Column() {
        println("Composed with $observeAsState and pos: ${textRingPosition}expected value: ${rememberTextRingPosition.value}")
        Text("Text: $observeAsState")
        Button(onClick = {
            textRingPosition = textRingPosition.inc().rem(textRing.size)
            rememberTextRingPosition.value = rememberTextRingPosition.value.inc().rem(textRing.size)
            println("OnClick: var:$textRingPosition remember: ${rememberTextRingPosition.value}")
            liveData.postValue(textRing[textRingPosition])
        }) {
            Text("change")
        }
    }
}

输出：

1 | I/System.out: Composed with one and pos: 0expected value: 0
2 | I/System.out: OnClick: var:1 remember: 1
3 | I/System.out: Composed with two and pos: 0expected value: 1
4 | I/System.out: OnClick: var:1 remember: 2
5 | I/System.out: Composed with two and pos: 0expected value: 2
6 | I/System.out: OnClick: var:1 remember: 0
7 | I/System.out: Composed with two and pos: 0expected value: 0
8 | I/System.out: OnClick: var:1 remember: 1

如日志所述，组件每次都会按应有的方式重新组合，并且不会因为记忆而重置状态。

Answer 2

AndroidView() 可组合项默认情况下不会在状态更改时重新组合。您必须通过显式定义更新参数来“选择加入”以收听状态。

所以语法应该是这样的：

@Composable
fun TraditionalViewAsComposable(initialString:String){
    var updatableString by remember{mutableStateOf("")}
    AndroidView(factory={it:Context->
        TraditionalView(it).apply{this:TraditionalView->
            this.property=initialString
        },
        update={it:TraditionalView->
            it.property=updatableString
            },
        modifier=Modifier
        )
}

如何在创建它的参数发生变化时替换 Android Jetpack Compose AndroidView？

How can I make Android Jetpack Compose AndroidView be replaced when the parameters that created it change?

android

android-view

kotlin

android-jetpack-compose