更改创建它的参数后，如何替换Android Jetpack Compose AndroidView？

问题描述

我有一个应用程序，它显示封装在AndroidView中的几种不同视图。在下面要重现的简单示例中，这些只是TextView实例。问题在于更改文本（在这种情况下，通过三个不同的值循环）似乎并没有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函数显示并起作用，第二个文本带有TextView包装的AndroidView Compose函数并且不起作用，第三个也使用相同的AndroidView包装器，但通过使用另一个状态变量以某种方式触发了更改。

为什么中间文本不更新？

具有hack修复程序https://gist.github.com/okhobb/ba7791af4562ea672d0c52769a7cd8ba

的可复制kt文件的完整摘要

解决方法

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

作为一般性提示，如果您的撰写代码包含var，则可能是错误的，应该是一种状态。

说明：如果您运行此代码段，请按下按钮，但是composable不会更新，但是在控制台中您会看到该值已更改。

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")
        }
    }
}

控制台中的输出：

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，但是它应该已经在2处，这是因为视图在第3行中重新组成并重置了索引。由于当前视图的值与状态中的新值相同，因此视图不需要更新，因此此处不会重新组合。在第5行中，索引为2，它将状态值更改为另一个字符串，从而触发了重新组合。

具有索引的记忆状态和可变状态，该组件将重新组合每次更改：

Surface(modifier = Modifier.padding(all = 16.dp).fillMaxSize()) {
    val textRing = arrayOf("one","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

作为日志状态，组件将按应有的方式每次进行重组，并且由于记忆而不会重置状态。

android android android-jetpack-compose android-view kotlin kotlin kotlin