实现步骤
先红色画个爱心
Icon(
Icons.Filled.Favorite,
"爱心",
Modifier
.align(Alignment.Center)
tint = Color.Red
)点击事件加动画
双击监听
.pointerInput(Unit) {
detectTapGestures(
onDoubleTap = {
...
}
)
}
#### **API 介绍**
| API名称 | 作用 |
| --- | --- |
| detectTapGestures | 监听点击手势 |
> 与 Clickable Modifier 不同的是，detectTapGestures 可以监听更多的点击事件。作为手机监听的基础 API，必然不会存在 Clickable Modifier 所拓展的涟漪效果
detectTapGestures 提供了四个可选参数
- onDoubleTap (可选)：双击时回调
- onLongPress (可选)：长按时回调
- onPress (可选)：按下时回调
- onTap (可选)：轻触时回调
我们用到的就是`onDoubleTap`用枚举定义三个变量 开始、显示和消失
enum class LikedStates {
Initial,
Liked,
Disappeared
}remember保持数据状态，mutableStateOf监听状态变化
var transitionState by remember {
mutableStateOf(MutableTransitionState(LikedStates.Disappeared))
}MutableTransitionState包含两个字段：currentState和targetState。currentState初始化为提供的initialState，并且只能通过转换进行变异。targetState也初始化为initialState。可以对其进行变异，以改变使用updateTransition使用MutableTransitionState创建的过渡动画的过程。currentState和targetState都由状态对象支持。
判断拦截数据变化过程，用于实现对应的动画
if (transitionState.currentState == LikedStates.Initial) {
transitionState.targetState = LikedStates.Liked
} else if (transitionState.currentState == LikedStates.Liked) {
transitionState.targetState = LikedStates.Disappeared
}开始显示的过度动画
val transition = updateTransition(transitionState = transitionState, label = null)
val alpha by transition.animateFloat(
transitionSpec = {
...
}
) {
if (it == LikedStates.Liked) 1f else 0f
}我们要实现有弹性的放大动画，所以利用graphicsLayer实现缩放
graphicsLayer可以应用于
- 缩放（
scaleX、scaleY） - 旋转（rotationX、rotationY、rotationZ）
- 不透明度（
alpha） - 阴影（shadowElevation、shape）
- 剪裁（clip、shape）
定义scale,XY
1 ：1放大所以定义一个就行
val scale by transition.animateFloat(
transitionSpec = {
....
}
) {
...
}创建浮动动画作为给定变换的一部分targetValueByState用作从目标状态到此动画的目标值的映射
最后在定义三种状态里吗设置对应的参数
when (it) {
LikedStates.Initial -> 0f
LikedStates.Liked -> 4f
LikedStates.Disappeared -> 2f
}完整代码
@Suppress("TransitionPropertiesLabel")
@Composable
fun DoubleTapToLike() {
var transitionState by remember {
mutableStateOf(MutableTransitionState(LikedStates.Disappeared))
}
Box(
Modifier
.fillMaxSize()
.pointerInput(Unit) {
detectTapGestures(
onDoubleTap = {
transitionState = MutableTransitionState(LikedStates.Initial)
}
)
}
) {
if (transitionState.currentState == LikedStates.Initial) {
transitionState.targetState = LikedStates.Liked
} else if (transitionState.currentState == LikedStates.Liked) {
transitionState.targetState = LikedStates.Disappeared
}
val transition = updateTransition(transitionState = transitionState, label = null)
val alpha by transition.animateFloat(
transitionSpec = {
when {
LikedStates.Initial isTransitioningTo LikedStates.Liked ->
keyframes {
durationMillis = 500
0f at 0
0.5f at 100
1f at 225
}
LikedStates.Liked isTransitioningTo LikedStates.Disappeared ->
tween(durationMillis = 200)
else -> snap()
}
}
) {
if (it == LikedStates.Liked) 1f else 0f
}
val scale by transition.animateFloat(
transitionSpec = {
when {
LikedStates.Initial isTransitioningTo LikedStates.Liked ->
spring(dampingRatio = Spring.DampingRatioHighBouncy)
LikedStates.Liked isTransitioningTo LikedStates.Disappeared ->
tween(200)
else -> snap()
}
}
) {
when (it) {
LikedStates.Initial -> 0f
LikedStates.Liked -> 4f
LikedStates.Disappeared -> 2f
}
}
Icon(
Icons.Filled.Favorite,
"点赞",
Modifier
.align(Alignment.Center)
.graphicsLayer(
alpha = alpha,
scaleX = scale,
scaleY = scale
),
tint = Color.Red
)
}
}
enum class LikedStates {
Initial,
Liked,
Disappeared
}效果图
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