android - Jetpack Compose - LazyColumnFor 在添加项目时不重新组合

Question

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更改时自动更新，但它不会更新，并且在最初组成之后我无法将项目添加到 LazyColumnFor。

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中的按钮只是为了测试添加一个项目。据我了解，LazyColumnFor 应该在基础数据发生更改时更新，类似于 SwiftUI 中的 ForEach。我究竟做错了什么？

标签： androidkotlinandroid-jetpack-compose

Answer 1

Jetpack compose 始终需要在进行重组之前修改状态对象。您需要使用MutableStateList<T>. 您可以传递对它的引用并以任何接受的方法进行更新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
                )
            )
        }) {

        }
    }
}