Switch组件使用。
Row 封装开关提示例子
KeyboardActions 的使用
FocusManager 的使用

import androidx.annotation.StringRes
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.text.KeyboardActions
import androidx.compose.foundation.text.KeyboardOptions
import androidx.compose.material.Switch
import androidx.compose.material.SwitchDefaults
import androidx.compose.material.Text
import androidx.compose.material.TextField
import androidx.compose.runtime.*
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.focus.FocusDirection
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.platform.LocalFocusManager
import androidx.compose.ui.res.stringResource
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.text.input.ImeAction
import androidx.compose.ui.text.input.KeyboardType
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.sp
import java.text.NumberFormat

@Composable
fun TipTimeScreen() {
    var amountInput by remember {
        mutableStateOf("")
    }
    var tipInput by remember { mutableStateOf("") }
    val tipPercent = tipInput.toDoubleOrNull() ?: 0.0
    val amount = amountInput.toDoubleOrNull() ?: 0.0
    val focusManager = LocalFocusManager.current
    var roundUp by remember { mutableStateOf(false) }
    val tip = calculateTIp(amount, tipPercent, roundUp = roundUp)

    Column(
        modifier = Modifier.padding(32.dp),
        verticalArrangement = Arrangement.spacedBy(8.dp)
    ) {
        Text(
            text = stringResource(id = R.string.calculate_tip),
            fontSize = 24.sp,
            modifier = Modifier.align(Alignment.CenterHorizontally)
        )
        Spacer(modifier = Modifier.height(16.dp))
        EditNumberField(
            R.string.bill_amount,
            keyboardOptions = KeyboardOptions.Default.copy(
                keyboardType = KeyboardType.Number,
                imeAction = ImeAction.Next
            ),
            KeyboardActions(onNext = {
                focusManager.moveFocus(FocusDirection.Down)
            }),
            value = amountInput,
            onValueChange = { amountInput = it })
        EditNumberField(
            R.string.how_was_the_service,
            keyboardOptions = KeyboardOptions.Default.copy(
                keyboardType = KeyboardType.Number,
                imeAction = ImeAction.Done
            ),
            KeyboardActions(onDone = {
                focusManager.clearFocus()
            }),
            value = tipInput,
            onValueChange = { tipInput = it })

        RoundTheTipRow(roundUp = roundUp, onRoundUpChanged = { roundUp = it })
        Spacer(Modifier.height(24.dp))
        Text(
            text = stringResource(R.string.tip_amount, tip),
            modifier = Modifier.align(Alignment.CenterHorizontally),
            fontSize = 20.sp,
            fontWeight = FontWeight.Bold
        )
    }
}

@Composable
fun EditNumberField(
    @StringRes label: Int,
    keyboardOptions: KeyboardOptions,
    keyboardActions: KeyboardActions,
    value: String,
    onValueChange: (String) -> Unit
) {
    TextField(
        value = value,

        onValueChange = onValueChange,
        modifier = Modifier.fillMaxWidth(),
        label = { Text(text = stringResource(label)) },
        singleLine = true,
        keyboardOptions = keyboardOptions,
        keyboardActions = keyboardActions
    )
}


@Composable
fun RoundTheTipRow(
    roundUp: Boolean, onRoundUpChanged: (Boolean) -> Unit,
    modifier: Modifier = Modifier
) {
    Row(
        modifier = modifier
            .fillMaxWidth()
            .size(48.dp),
        verticalAlignment = Alignment.CenterVertically
    ) {
        Text(stringResource(R.string.round_up_tip))
        Switch(
            modifier = Modifier
                .fillMaxWidth()
                .wrapContentWidth(Alignment.End),
            checked = roundUp,
            onCheckedChange = onRoundUpChanged,
            colors = SwitchDefaults.colors(
                uncheckedThumbColor = Color.DarkGray
            )
        )
    }
}


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)
}

使用

class MainActivity : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            GreetingCardTheme {
                // A surface container using the 'background' color from the theme
                Surface(
                    modifier = Modifier.fillMaxSize(),
                    color = MaterialTheme.colors.background
                ) {
                    TipTimeScreen()
                }
            }
        }
    }
}


@Preview(showBackground = true, showSystemUi = true)
@Composable
fun DefaultPreview() {
    GreetingCardTheme {
        Surface(
            modifier = Modifier.fillMaxSize(),
            color = MaterialTheme.colors.background
        ) {
            TipTimeScreen()
        }
    }
}