Jetpack Compose - LazyColumn 用于在添加项目时不重新组合 [英] Jetpack Compose - LazyColumnFor not recomposing when item added

问题描述

我正在尝试在 Jetpack Compose 中创建一个项目列表，该列表会在基础数据发生更改时自动更新，但它不会更新，并且我无法在初始组合后将项目添加到 LazyColumnFor.

I am trying to create a list of items in Jetpack Compose that automatically updates whenever the underlying data changes, but it is not updating and I cannot add an item to the LazyColumnFor after it has initially composed.

private var latestMessages = mutableListOf<ChatMessage>()

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View {
    return ComposeView(context = requireContext()).apply {
        setContent {
            LatestMessages(latestMessages)
        }
    }
}

@Composable
fun LatestMessages(messages: MutableList<ChatMessage>) {
    Column {
        LazyColumnFor(items = messages) { chatMessage ->
            LatestMessageItem(chatMessage) {
                // onclick
            }
        }
    }
    Box(alignment = Alignment.Center) {
        Button(onClick = {
            latestMessages.add(
                    ChatMessage(
                            "testId",
                            "testText2",
                            "testFromId2",
                            "testToId",
                            "timestamp",
                            0
                    )
            )
        }) {

        }
    }
}

Box 中的 Button 只是为了测试添加一个项目.据我了解 LazyColumnFor 应该在底层数据发生更改时更新，类似于 SwiftUI 中的 ForEach.我做错了什么?

The Button in the Box is just to test adding an item. From what I understand LazyColumnFor should update whenever the underlying data is changed, similar to ForEach in SwiftUI. What am I doing wrong?

推荐答案

Jetpack compose 总是需要在重新组合发生之前修改一个状态对象.您需要使用 MutableStateList.您可以传递对它的引用并在任何接受 SnapShotStateList

Jetpack compose always needs a state object to be modified before recomposition can occur. You need to use a MutableStateList<T>. You can pass a reference to it around and update in any method which accepts a SnapShotStateList<T>

override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
): View {
    
    return ComposeView(context = requireContext()).apply {
        setContent {
            val latestMessages = mutableStateListOf<ChatMessage>()
            LatestMessages(latestMessages)
        }
    }
}

@Composable
fun LatestMessages(messages: SnapshotStateList<ChatMessage>) {
    Column {
        LazyColumnFor(items = messages) { chatMessage ->
            LatestMessageItem(chatMessage) {
                // onclick
            }
        }
    }
    Box(alignment = Alignment.Center) {
        Button(onClick = {
            latestMessages.add(
                ChatMessage(
                    "testId",
                    "testText2",
                    "testFromId2",
                    "testToId",
                    "timestamp",
                    0
                )
            )
        }) {

        }
    }
}

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