Jetpack compose 的公开下拉菜单

Question

我想知道是否有针对 jetpack compose 的 Exposed 下拉菜单的解决方案？ 我在 jetpack compose 中找不到这个组件的合适解决方案。有什么帮助吗？

Answer 1

1.1.0-alpha06版本在ExposedDropdownMenuBox的基础上引入了ExposedDropdownMenu的实现，里面有TextField和DropdownMenu。

类似：

    val options = listOf("Option 1", "Option 2", "Option 3", "Option 4", "Option 5")
    var expanded by remember { mutableStateOf(false) }
    var selectedOptionText by remember { mutableStateOf(options[0]) }
    
    ExposedDropdownMenuBox(
        expanded = expanded,
        onExpandedChange = {
            expanded = !expanded
        }
    ) {
        TextField(
            readOnly = true,
            value = selectedOptionText,
            onValueChange = { },
            label = { Text("Label") },
            trailingIcon = {
                ExposedDropdownMenuDefaults.TrailingIcon(
                    expanded = expanded
                )
            },
            colors = ExposedDropdownMenuDefaults.textFieldColors()
        )
        ExposedDropdownMenu(
            expanded = expanded,
            onDismissRequest = {
                expanded = false
            }
        ) {
            options.forEach { selectionOption ->
                DropdownMenuItem(
                    onClick = {
                        selectedOptionText = selectionOption
                        expanded = false
                    }
                ) {
                    Text(text = selectionOption)
                }
            }
        }
    }

1.0.x 版本没有内置组件。
您可以使用OutlinedTextField + DropdownMenu。

这只是一个基本的（非常基本的）实现：

var expanded by remember { mutableStateOf(false) }
val suggestions = listOf("Item1","Item2","Item3")
var selectedText by remember { mutableStateOf("") }

var textfieldSize by remember { mutableStateOf(Size.Zero)}

val icon = if (expanded)
    Icons.Filled.ArrowDropUp //it requires androidx.compose.material:material-icons-extended
else
    Icons.Filled.ArrowDropDown


Column() {
    OutlinedTextField(
        value = selectedText,
        onValueChange = { selectedText = it },
        modifier = Modifier
            .fillMaxWidth()
            .onGloballyPositioned { coordinates ->
                //This value is used to assign to the DropDown the same width
                textfieldSize = coordinates.size.toSize()
            },
        label = {Text("Label")},
        trailingIcon = {
            Icon(icon,"contentDescription",
                 Modifier.clickable { expanded = !expanded })
        }
    )
    DropdownMenu(
        expanded = expanded,
        onDismissRequest = { expanded = false },
        modifier = Modifier
            .width(with(LocalDensity.current){textfieldSize.width.toDp()})
    ) {
        suggestions.forEach { label ->
            DropdownMenuItem(onClick = {
                selectedText = label
            }) {
                Text(text = label)
            }
        }
    }
}

Answer 2

这是我为使宽度与文本字段相同所做的操作：复制和修改 Gabriele 的答案。

var expanded by remember { mutableStateOf(false) }
val suggestions = listOf("Item1","Item2","Item3")
var selectedText by remember { mutableStateOf("") }

var dropDownWidth by remember { mutableStateOf(0) }

val icon = if (expanded)
    Icons.Filled.....
else
    Icons.Filled.ArrowDropDown


Column() {
    OutlinedTextField(
        value = selectedText,
        onValueChange = { selectedText = it },
        modifier = Modifier.fillMaxWidth()
            .onSizeChanged {
                dropDownWidth = it.width
            },
        label = {Text("Label")},
        trailingIcon = {
            Icon(icon,"contentDescription", Modifier.clickable { expanded = !expanded })
        }
    )
    DropdownMenu(
        expanded = expanded,
        onDismissRequest = { expanded = false },
        modifier = Modifier
                .width(with(LocalDensity.current){dropDownWidth.toDp()})
    ) {
        suggestions.forEach { label ->
            DropdownMenuItem(onClick = {
                selectedText = label
            }) {
                Text(text = label)
            }
        }
    }
}

Answer 3

这是我的版本。 我在没有使用TextField 的情况下实现了这一点（所以没有键盘）。 有“常规”和“轮廓”两种版本。

import androidx.compose.animation.core.animateFloatAsState
import androidx.compose.foundation.background
import androidx.compose.foundation.border
import androidx.compose.foundation.clickable
import androidx.compose.foundation.layout.*
import androidx.compose.foundation.shape.ZeroCornerSize
import androidx.compose.material.*
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.ExpandMore
import androidx.compose.runtime.*
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.draw.drawBehind
import androidx.compose.ui.draw.rotate
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.geometry.Size
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.Shape
import androidx.compose.ui.layout.onGloballyPositioned
import androidx.compose.ui.platform.LocalDensity
import androidx.compose.ui.platform.LocalFocusManager
import androidx.compose.ui.unit.Dp
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.toSize
import kotlinx.coroutines.delay
import kotlinx.coroutines.launch


// ExposedDropDownMenu will be added in Jetpack Compose 1.1.0.
// This is a reimplementation while waiting.
// See https://stackoverflow.com/questions/67111020/exposed-drop-down-menu-for-jetpack-compose/6904285

@Composable
fun SimpleExposedDropDownMenu(
    values: List<String>,
    selectedIndex: Int,
    onChange: (Int) -> Unit,
    label: @Composable () -> Unit,
    modifier: Modifier,
    backgroundColor: Color = MaterialTheme.colors.onSurface.copy(alpha = TextFieldDefaults.BackgroundOpacity),
    shape: Shape = MaterialTheme.shapes.small.copy(bottomEnd = ZeroCornerSize, bottomStart = ZeroCornerSize)
) {
    SimpleExposedDropDownMenuImpl(
        values = values,
        selectedIndex = selectedIndex,
        onChange = onChange,
        label = label,
        modifier = modifier,
        backgroundColor = backgroundColor,
        shape = shape,
        decorator = { color, width, content ->
            Box(
                Modifier
                    .drawBehind {
                        val strokeWidth = width.value * density
                        val y = size.height - strokeWidth / 2
                        drawLine(
                            color,
                            Offset(0f, y),
                            Offset(size.width, y),
                            strokeWidth
                        )
                    }
            ) {
                content()
            }
        }
    )
}

@Composable
fun SimpleOutlinedExposedDropDownMenu(
    values: List<String>,
    selectedIndex: Int,
    onChange: (Int) -> Unit,
    label: @Composable () -> Unit,
    modifier: Modifier,
    backgroundColor: Color = MaterialTheme.colors.onSurface.copy(alpha = TextFieldDefaults.BackgroundOpacity),
    shape: Shape = MaterialTheme.shapes.small
) {
    SimpleExposedDropDownMenuImpl(
        values = values,
        selectedIndex = selectedIndex,
        onChange = onChange,
        label = label,
        modifier = modifier,
        backgroundColor = backgroundColor,
        shape = shape,
        decorator = { color, width, content ->
            Box(
                Modifier
                    .border(width, color, shape)
            ) {
                content()
            }
        }
    )
}

@Composable
private fun SimpleExposedDropDownMenuImpl(
    values: List<String>,
    selectedIndex: Int,
    onChange: (Int) -> Unit,
    label: @Composable () -> Unit,
    modifier: Modifier,
    backgroundColor: Color,
    shape: Shape,
    decorator: @Composable (Color, Dp, @Composable () -> Unit) -> Unit
) {
    var expanded by remember { mutableStateOf(false) }
    var textfieldSize by remember { mutableStateOf(Size.Zero) }

    val indicatorColor =
        if (expanded) MaterialTheme.colors.primary.copy(alpha = ContentAlpha.high)
        else MaterialTheme.colors.onSurface.copy(alpha = TextFieldDefaults.UnfocusedIndicatorLineOpacity)
    val indicatorWidth = (if (expanded) 2 else 1).dp
    val labelColor =
        if (expanded) MaterialTheme.colors.primary.copy(alpha = ContentAlpha.high)
        else MaterialTheme.colors.onSurface.copy(ContentAlpha.medium)
    val trailingIconColor = MaterialTheme.colors.onSurface.copy(alpha = TextFieldDefaults.IconOpacity)

    val rotation: Float by animateFloatAsState(if (expanded) 180f else 0f)

    val focusManager = LocalFocusManager.current

    Column(modifier = modifier.width(IntrinsicSize.Min)) {
        decorator(indicatorColor, indicatorWidth) {
            Box(
                Modifier
                    .fillMaxWidth()
                    .background(color = backgroundColor, shape = shape)
                    .onGloballyPositioned { textfieldSize = it.size.toSize() }
                    .clip(shape)
                    .clickable {
                        expanded = !expanded
                        focusManager.clearFocus()
                    }
                    .padding(start = 16.dp, end = 12.dp, top = 7.dp, bottom = 10.dp)
            ) {
                Column(Modifier.padding(end = 32.dp)) {
                    ProvideTextStyle(value = MaterialTheme.typography.caption.copy(color = labelColor)) {
                        label()
                    }
                    Text(
                        text = values[selectedIndex],
                        modifier = Modifier.padding(top = 1.dp)
                    )
                }
                Icon(
                    imageVector = Icons.Filled.ExpandMore,
                    contentDescription = "Change",
                    tint = trailingIconColor,
                    modifier = Modifier
                        .align(Alignment.CenterEnd)
                        .padding(top = 4.dp)
                        .rotate(rotation)
                )

            }
        }

        DropdownMenu(
            expanded = expanded,
            onDismissRequest = { expanded = false },
            modifier = Modifier
                .width(with(LocalDensity.current) { textfieldSize.width.toDp() })
        ) {
            values.forEachIndexed { i, v ->
                val scope = rememberCoroutineScope()
                DropdownMenuItem(
                    onClick = {
                        onChange(i)
                        scope.launch {
                            delay(150)
                            expanded = false
                        }
                    }
                ) {
                    Text(v)
                }
            }
        }
    }
}