deriveStateOf 变化时触发回调

Question

我想在

derivedStateOf

发生变化时触发回调。我的代码目前如下所示：

var previouslySelectedIndex by rememberSaveable { mutableStateOf<Int?>(null) }

val nowSelectedIndex by remember {
    derivedStateOf {
        // some logic here
    }
}

nowSelectedIndex?.let { nowSelected ->
    if(previouslySelectedIndex == null || previouslySelectedIndex != nowSelected) {
        previouslySelectedIndex = nowSelected
        onSelectedItemChanged(nowSelected)
    }
}

这对我来说非常冗长，特别是考虑到我们知道

derivedStateOf

仅在更改时才会触发。真的没有像下面这样的吗？

nowSelectedIndex.onChange { onSelectedItemChanged(nowSelected) }

Answer 1

您可能想查看

LaunchedEffect

。当

key

的值发生变化时会触发该块。

LaunchedEffect(nowSelectedIndex) {
    onSelectedItemChanged(nowSelected)
}