Kolin状态提升以及输入框

@Composable
fun TipTimeLayout() {
    var amountInput by remember { mutableStateOf("") }
    var tipInput by remember { mutableStateOf("") }
    // Switch 可组合项状态
    var roundUp by remember { mutableStateOf(false) }

    // 转换为double输入为空时值为0.0
    val amount = amountInput.toDoubleOrNull() ?: 0.0
    val tipPercent = tipInput.toDoubleOrNull() ?: 0.0
    
    val tip = calculateTip(amount, tipPercent, roundUp)

    Column(
        modifier = Modifier
            .statusBarsPadding()
            .padding(horizontal = 40.dp)
            // 允许上下滚动
            .verticalScroll(rememberScrollState())
            .safeDrawingPadding(),
        horizontalAlignment = Alignment.CenterHorizontally,
        verticalArrangement = Arrangement.Center
    ) {
        Text(
            text = stringResource(R.string.calculate_tip),
            modifier = Modifier
                .padding(bottom = 16.dp, top = 40.dp)
                .align(alignment = Alignment.Start)
        )
        EditNumberField(
            label = R.string.bill_amount,
            leadingIcon = R.drawable.money,
            keyboardOptions = KeyboardOptions.Default.copy(
                keyboardType = KeyboardType.Number,
                imeAction = ImeAction.Next
            ),
            value = amountInput,
            onValueChange = { amountInput = it },
            modifier = Modifier
                .padding(bottom = 32.dp)
                .fillMaxWidth()

        )
        EditNumberField(
            label = R.string.how_was_the_service,
            leadingIcon = R.drawable.percent,
            keyboardOptions = KeyboardOptions.Default.copy(
                keyboardType = KeyboardType.Number,
                imeAction = ImeAction.Done
            ),
            value = tipInput,
            onValueChange = { tipInput = it },
            modifier = Modifier
                .padding(bottom = 32.dp)
                .fillMaxWidth(),

            )
        RoundTheTipRow(
            roundUp = roundUp,
            onRoundUpChanged = { roundUp = it },
            modifier = Modifier.padding(bottom = 32.dp)
        )
        Text(
            text = stringResource(R.string.tip_amount, tip),
            style = MaterialTheme.typography.displaySmall
        )
        Spacer(modifier = Modifier.height(150.dp))
    }
}

@Composable
fun RoundTheTipRow(
    roundUp: Boolean,
    onRoundUpChanged: (Boolean) -> Unit,
    modifier: Modifier = Modifier
) {
    Row(
        modifier = modifier.fillMaxWidth(),
        verticalAlignment = Alignment.CenterVertically
    ) {
        Text(text = stringResource(R.string.round_up_tip))

        Switch(
            checked = roundUp,
            onCheckedChange = onRoundUpChanged,
            modifier = Modifier
                .fillMaxWidth()
                .wrapContentWidth(Alignment.End)
        )
    }
}

/**
 * 用到了状态提升，提高了可复用性
 * @param label 标签
 * @param leadingIcon 前置图标
 * @param keyboardOptions 键盘类型
 */
@Composable
fun EditNumberField(
    @StringRes label: Int,
    @DrawableRes leadingIcon: Int,
    keyboardOptions: KeyboardOptions,
    value: String,
    onValueChange: (String) -> Unit,
    modifier: Modifier = Modifier
) {
    TextField(
        value = value,
        leadingIcon = { Icon(painter = painterResource(id = leadingIcon), null) },
        onValueChange = onValueChange,
        singleLine = true,
        label = { Text(stringResource(label)) },
        keyboardOptions = keyboardOptions,
        modifier = modifier
    )
}

private fun calculateTip(
    amount: Double,
    tipPercent: Double = 15.0,
    roundUp: Boolean
): String {
    var tip = tipPercent / 100 * amount
    if (roundUp) {
        tip = kotlin.math.ceil(tip)
    }
    return NumberFormat.getCurrencyInstance().format(tip)
}