前景背景面板的布局在2022年的今天应用市场上应该绝大部分 APP 都采用了，特别是比如地图，打车，购物，直播 APP（带货）下面的面板交互实现
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在 Android View 体系中，需要实现前景背景面板还挺麻烦的，通常的方案如下：
- 1、xml 中实现 FrameLayout，分别放置前景板布局和背景布局
- 2、定义前景面板的拖动状态
- 3、拦截事件分发控制前景面板的拖动，控制滑动范围（或者用 ViewDragHelper 实现自定义拖动和动画控制，也要相当大的代码量才能精确控制）
- 4、实现某个状态点附近的回弹动画
GitHub 中有很多类似的开源方案，其中 Star 最多的是 AndroidSlidingUpPanel，其核心实现类 AndroidSlidingUpPanel 也有将近1500行。
Compose 版本实现理论上和 View 体系实现差不多，无非也就是布局，拖动控制，范围控制
-
布局：能画出来就行，通常都是用 Box
-
拖动控制：Modifier的扩展千奇百样，特别是手势相关的，最基础的无非是使用
Modifier.pointerInput()纯控制事件分发来控制布局（类似 View 体系）。而且还有逻辑高度封装的draggable修饰符或者swipeable修饰符可以使用，这里我们要拖动并且也要可以动画控制滑动，采用swipeable修饰符即可，配合SwipeableState就可以控制滑动或者动画 -
范围控制：
swipeable修饰符直接自带！！！
上来肯定是先画出布局，这里直接无脑 Box Box Box，Box 三连
@Composable
fun SlidingUpPanel(
backgroundContent: @Composable BoxScope.() -> Unit,
foregroundContent: @Composable BoxScope.() -> Unit
) {
Box(
modifier = Modifier.fillMaxSize()
) {
Box(
modifier = Modifier.fillMaxSize()
) {
backgroundContent()
}
Box(
modifier = Modifier
.fillMaxSize()
) {
foregroundContent()
}
}
}
根据官方文档 手势 | Jetpack Compose | Android Developers 的描述和示范例子，还有 swipeable 修饰符的文档描述，惊了大离谱吧，swipeable 不仅可以让布局滑动，还可以通过 anchors 来控制滑动状态点的距离，甚至还可以动画回弹
@OptIn(ExperimentalMaterialApi::class)
@Composable
fun SlidingUpPanel(
swipeableState: SwipeableState<PanelStateEnum> = rememberSwipeableState(PanelStateEnum.COLLAPSED),
enabled: Boolean = true,
backgroundContent: @Composable BoxScope.() -> Unit,
foregroundContent: @Composable BoxScope.() -> Unit
) {
val anchors = remember {
mapOf(
0F to PanelStateEnum.EXPANDED,
200F to PanelStateEnum.ANCHORED,
500F to PanelStateEnum.COLLAPSED,
900F to PanelStateEnum.HIDDEN,
)
}
Box(
modifier = Modifier.fillMaxSize()
) {
Box(
modifier = Modifier.fillMaxSize()
) {
backgroundContent()
}
Box(modifier = Modifier
.offset {
IntOffset(x = 0, y = swipeableState.offset.value.roundToInt())
}
.fillMaxSize()
.swipeable(
state = swipeableState,
anchors = anchors,
orientation = Orientation.Vertical,
enabled = enabled
)) {
foregroundContent()
}
}
}
就这样就已经支持4个状态的滑动控制+边界控制+边界回弹啦！！！
上述 anchors 其实只需要 ANCHORED点的偏移和 COLLAPSED 偏移值就好了，定义一个类输入和保存传递相关的值
/**
*
* 保存了面板偏移高度相关的参数，偏移量指从上往下
*
* @property context Context
* @property anchoredOffsetRatio Double anchored 状态偏移占屏幕高度的比例
* @property collapsedOffsetRatio Double collapsed 状态偏移占屏幕高度的比例
* @property screenHeight Int 屏幕高度
* @property anchoredOffset Float anchored 状态偏移
* @property collapsedOffset Float collapsed 状态偏移
* @property hiddenOffset Float hidden 状态偏移
* @constructor
*/
data class PanelStateOffset(
val context: Context,
var anchoredOffsetRatio: Double = 0.25,
var collapsedOffsetRatio: Double = 0.75,
var screenHeight: Int = screenHeight(context),
private var anchoredOffset: Float = 0f,
private var collapsedOffset: Float = 0f,
val hiddenOffset: Float = screenHeight.toFloat(),
) {
fun anchoredOffset() = (screenHeight * anchoredOffsetRatio).toFloat()
fun collapsedOffset() = (screenHeight * collapsedOffsetRatio).toFloat()
fun setOffsetRatio(
anchoredOffsetRatio: Double, collapsedOffsetRatio: Double, screenHeight: Int = -1
) {
this.anchoredOffsetRatio = anchoredOffsetRatio
this.collapsedOffsetRatio = collapsedOffsetRatio
this.screenHeight = if (screenHeight != -1) screenHeight else this.screenHeight
}
companion object {
/**
* 物理尺寸高度
*
* @param context Context
* @return Int
*/
@Stable
fun screenHeight(context: Context): Int {
val wm = context.getSystemService(Context.WINDOW_SERVICE) as WindowManager? ?: return -1
val point = Point()
wm.defaultDisplay.getRealSize(point)
return point.y
}
}
}
SlidingUpPanel 最终代码变为
/**
* 前景背景面板布局
*
* @param initialPanelState [PanelStateEnum] 面板初始化状态
* @param swipeableState SwipeableState<PanelStateEnum> swipeable修饰符的状态
* @param panelStateOffset [@kotlin.ExtensionFunctionType] Function2<PanelStateOffset, Int, Unit> 可以预设面板的各个高度参数
* @param enabled Boolean 是否开启滑动
* @param backgroundContent [@androidx.compose.runtime.Composable] [@kotlin.ExtensionFunctionType] Function1<BoxScope, Unit> 背景布局
* @param foregroundContent [@androidx.compose.runtime.Composable] [@kotlin.ExtensionFunctionType] Function1<BoxScope, Unit> 前景布局
*/
@OptIn(ExperimentalMaterialApi::class)
@Composable
fun SlidingUpPanel(
initialPanelState: PanelStateEnum = PanelStateEnum.COLLAPSED,
swipeableState: SwipeableState<PanelStateEnum> = rememberSwipeableState(initialPanelState),
panelStateOffset: PanelStateOffset.(Int) -> Unit = {},
enabled: Boolean = true,
backgroundContent: @Composable BoxScope.() -> Unit,
foregroundContent: @Composable BoxScope.() -> Unit
) {
val context = LocalContext.current
val panelOffset = remember {
PanelStateOffset(context)
}
panelStateOffset.invoke(panelOffset, panelOffset.screenHeight)
val anchors = remember {
mapOf(
0F to PanelStateEnum.EXPANDED,
panelOffset.anchoredOffset() to PanelStateEnum.ANCHORED,
panelOffset.collapsedOffset() to PanelStateEnum.COLLAPSED,
panelOffset.hiddenOffset to PanelStateEnum.HIDDEN,
)
}
Box(
modifier = Modifier.fillMaxSize()
) {
Box(
modifier = Modifier.fillMaxSize()
) {
backgroundContent()
}
Box(modifier = Modifier
.offset {
IntOffset(x = 0, y = swipeableState.offset.value.roundToInt())
}
.fillMaxSize()
.swipeable(
state = swipeableState,
anchors = anchors,
orientation = Orientation.Vertical,
enabled = enabled
)) {
foregroundContent()
}
}
}
只需要和传统方式类似 Button，Box 一样使用即可
@OptIn(ExperimentalMaterialApi::class)
@Composable
fun Home() {
val scope = rememberCoroutineScope()
val swipeableState = rememberSwipeableState(PanelStateEnum.COLLAPSED)
SlidingUpPanel(swipeableState = swipeableState, panelStateOffset = {
this.collapsedOffsetRatio = 0.9
this.anchoredOffsetRatio = 0.1
}, backgroundContent = {
Box(modifier = Modifier
.border(width = 1.dp, color = Color.Black)
.fillMaxSize()
.background(Color.Green), contentAlignment = Alignment.TopCenter) {
BasicText(
"背景面板", style = TextStyle.Default.copy(color = Color.Red, fontSize = 25.sp)
)
ButtonColumn(scope, swipeableState)
}
}, foregroundContent = {
Box(
modifier = Modifier
.fillMaxSize()
.background(Color.Yellow)
.border(width = 1.dp, color = Color.Black),
contentAlignment = Alignment.TopCenter,
) {
BasicText(
"前景面板", style = TextStyle.Default.copy(color = Color.Red, fontSize = 25.sp)
)
ButtonColumn(scope, swipeableState)
}
})
}
有时候我们要根据业务情况来控制面板的移动，只需要通过 SwipeableState 的 animateTo()【有动画】 或者 snapTo()【无动画】控制即可
例如，让面板动画移动到 EXPANDED 状态只需要调用
swipeableState.animateTo(PanelStateEnum.EXPANDED)
Gif图巨大，耐心等待
minminaya/SlidingUpPanel-compose: SlidingUpPanel layout for Android Compose (github.com)
- 1、添加maven 地址
allprojects {
repositories {
...
maven { url 'https://jitpack.io' }
}
}- 2、声明依赖
dependencies {
implementation 'com.github.minminaya:SlidingUpPanel-compose:Tag'
}