状态依赖于另一个状态，Android Compose

Question

我有一个可组合对象，它获取一个可变状态的整数！

整数是一个计时器值！像 0 一样每秒增加一次

我必须在可组合内做的是转换为可表示的字符串，比如 60 秒，我将显示 1 分钟

所以我这样做

    val timeString = remember {
       mutableStateOf("00:00")
    }

    val durationString  = if(duration!=0) {
    var secondTime = ((duration / 1000) % 60).toString()
    var minuteTime = ((((duration / 1000) / 60) % 60)).toString()
    if (secondTime.length == 1) {
        secondTime = "0$secondTime"
    }
    if (minuteTime.length == 1) {
        minuteTime = "0$minuteTime"
    }
    "$minuteTime:$secondTime"
}else{
    "00:00"
}


timeString.value = durationString

         Text(
            modifier = Modifier
                .weight(1f)
                .padding(horizontal = 16.dp),
            text = timeString.value,
            style = MaterialTheme.typography.h4
        )

但是文本没有更新，但是由于持续时间是一个可变状态，如果我直接使用它，文本会更新，所以我尝试了 LaunchedEffect 但它没有用我想知道我能做到这一点的最佳方法是什么撰写！

Answer 1

就像我在评论中提到的那样，您需要扭曲每次在记忆中应该重新计算的内容，并将状态作为键传递（需要让 compose 知道它必须更新字符串）。

查看示例代码：

@Composable
fun outer() {
    val durationState = remember { mutableStateOf(600000) }
    LaunchedEffect(durationState) {
        // This not how you do a timer but close enough
        val step = 1000
        repeat(600000.div(step)) {
            durationState.value = durationState.value - step
            delay(step.toLong())
        }
    }
    questionComposable(durationState)
}

@Composable
fun questionComposable(durationState: MutableState<Int>) {
    val durationString = remember(durationState.value) {
        val duration = durationState.value
        if (duration != 0) {
            var secondTime = ((duration / 1000) % 60).toString()
            var minuteTime = ((((duration / 1000) / 60) % 60)).toString()
            if (secondTime.length == 1) {
                secondTime = "0$secondTime"
            }
            if (minuteTime.length == 1) {
                minuteTime = "0$minuteTime"
            }
            "$minuteTime:$secondTime"
        } else {
            "00:00"
        }

    }
    Text(
        text = durationString,
        style = MaterialTheme.typography.h4
    )
}