進階動畫範例:手勢
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與單獨處理動畫相比,同時處理觸控事件和動畫時,必須考慮幾個事項。首先,在觸控事件開始時,我們可能必須中斷處理中的動畫,因為使用者互動事件應該擁有最高的優先順序。
在以下範例中,我們使用 Animatable
表示圓形元件的偏移位置,並透過 pointerInput
修飾詞處理觸控事件。我們偵測到新的輕觸事件時,會呼叫 animateTo
建立從位移值移往輕觸位置的動畫效果。輕觸事件也可能會在出現動畫播放期間發生,在這種情況下,animateTo
會中斷目前執行的動畫,並讓動畫移向新的目標位置,同時維持已中斷動畫的速率。
@Composable
fun Gesture() {
val offset = remember { Animatable(Offset(0f, 0f), Offset.VectorConverter) }
Box(
modifier = Modifier
.fillMaxSize()
.pointerInput(Unit) {
coroutineScope {
while (true) {
// Detect a tap event and obtain its position.
awaitPointerEventScope {
val position = awaitFirstDown().position
launch {
// Animate to the tap position.
offset.animateTo(position)
}
}
}
}
}
) {
Circle(modifier = Modifier.offset { offset.value.toIntOffset() })
}
}
private fun Offset.toIntOffset() = IntOffset(x.roundToInt(), y.roundToInt())
另一個常見的模式是需要將動畫值與來自觸控事件 (例如拖曳) 的值同步處理。在以下範例中,我們會看到以 Modifier
(而不是使用 SwipeToDismiss
可組合項) 實作的「滑動關閉」動作。該元素的水平位移會以 Animatable
表示。這個 API 的特性適合在手勢動畫中使用。觸控事件和動畫都可以變更這個值。接收到觸控事件時,我們會透過 stop
方法停止 Animatable
,以便攔截任何執行中的動畫。
在拖曳事件期間,我們會使用 snapTo
將 Animatable
值更新為從觸控事件計算得出的值。針對快速滑過,Compose 可提供 VelocityTracker
來記錄拖曳事件並計算速率。該速率可直接動態饋給至 animateDecay
來執行快速滑過動畫。如要將位移值滑回原始位置,可使用 animateTo
方法指定 0f
的目標位移值。
fun Modifier.swipeToDismiss(
onDismissed: () -> Unit
): Modifier = composed {
val offsetX = remember { Animatable(0f) }
pointerInput(Unit) {
// Used to calculate fling decay.
val decay = splineBasedDecay<Float>(this)
// Use suspend functions for touch events and the Animatable.
coroutineScope {
while (true) {
val velocityTracker = VelocityTracker()
// Stop any ongoing animation.
offsetX.stop()
awaitPointerEventScope {
// Detect a touch down event.
val pointerId = awaitFirstDown().id
horizontalDrag(pointerId) { change ->
// Update the animation value with touch events.
launch {
offsetX.snapTo(
offsetX.value + change.positionChange().x
)
}
velocityTracker.addPosition(
change.uptimeMillis,
change.position
)
}
}
// No longer receiving touch events. Prepare the animation.
val velocity = velocityTracker.calculateVelocity().x
val targetOffsetX = decay.calculateTargetValue(
offsetX.value,
velocity
)
// The animation stops when it reaches the bounds.
offsetX.updateBounds(
lowerBound = -size.width.toFloat(),
upperBound = size.width.toFloat()
)
launch {
if (targetOffsetX.absoluteValue <= size.width) {
// Not enough velocity; Slide back.
offsetX.animateTo(
targetValue = 0f,
initialVelocity = velocity
)
} else {
// The element was swiped away.
offsetX.animateDecay(velocity, decay)
onDismissed()
}
}
}
}
}
.offset { IntOffset(offsetX.value.roundToInt(), 0) }
}
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上次更新時間:2025-08-27 (世界標準時間)。
[[["容易理解","easyToUnderstand","thumb-up"],["確實解決了我的問題","solvedMyProblem","thumb-up"],["其他","otherUp","thumb-up"]],[["缺少我需要的資訊","missingTheInformationINeed","thumb-down"],["過於複雜/步驟過多","tooComplicatedTooManySteps","thumb-down"],["過時","outOfDate","thumb-down"],["翻譯問題","translationIssue","thumb-down"],["示例/程式碼問題","samplesCodeIssue","thumb-down"],["其他","otherDown","thumb-down"]],["上次更新時間:2025-08-27 (世界標準時間)。"],[],[],null,["There are several things we have to take into consideration when we are working\nwith touch events and animations, compared to when we are working with\nanimations alone. First of all, we might need to interrupt an ongoing animation\nwhen touch events begin as user interaction should have the highest priority.\n\nIn the example below, we use an `Animatable` to represent the offset position of\na circle component. Touch events are processed with the\n[`pointerInput`](/reference/kotlin/androidx/compose/ui/input/pointer/package-summary#(androidx.compose.ui.Modifier).pointerInput(kotlin.Any,%20kotlin.coroutines.SuspendFunction1))\nmodifier. When we detect a new tap event, we call `animateTo` to animate the\noffset value to the tap position. A tap event can happen during the animation\ntoo, and in that case, `animateTo` interrupts the ongoing animation and starts\nthe animation to the new target position while maintaining the velocity of the\ninterrupted animation.\n\n\n```kotlin\n@Composable\nfun Gesture() {\n val offset = remember { Animatable(Offset(0f, 0f), Offset.VectorConverter) }\n Box(\n modifier = Modifier\n .fillMaxSize()\n .pointerInput(Unit) {\n coroutineScope {\n while (true) {\n // Detect a tap event and obtain its position.\n awaitPointerEventScope {\n val position = awaitFirstDown().position\n\n launch {\n // Animate to the tap position.\n offset.animateTo(position)\n }\n }\n }\n }\n }\n ) {\n Circle(modifier = Modifier.offset { offset.value.toIntOffset() })\n }\n}\n\nprivate fun Offset.toIntOffset() = IntOffset(x.roundToInt(), y.roundToInt())https://github.com/android/snippets/blob/5673ffc60b614daf028ee936227128eb8c4f9781/compose/snippets/src/main/java/com/example/compose/snippets/animations/AdvancedAnimationSnippets.kt#L62-L88\n```\n\n\u003cbr /\u003e\n\nAnother frequent pattern is we need to synchronize animation values with values\ncoming from touch events, such as drag. In the example below, we see \"swipe to\ndismiss\" implemented as a `Modifier` (rather than using the\n[`SwipeToDismiss`](/reference/kotlin/androidx/compose/material/package-summary#SwipeToDismiss(androidx.compose.material.DismissState,%20androidx.compose.ui.Modifier,%20kotlin.collections.Set,%20kotlin.Function1,%20kotlin.Function1,%20kotlin.Function1))\ncomposable). The horizontal offset of the element is represented as an\n`Animatable`. This API has a characteristic useful in gesture animation. Its\nvalue can be changed by touch events as well as the animation. When we receive a\ntouch down event, we stop the `Animatable` by the `stop` method so that any\nongoing animation is intercepted.\n\nDuring a drag event, we use `snapTo` to update the `Animatable` value with the\nvalue calculated from touch events. For fling, Compose provides\n`VelocityTracker` to record drag events and calculate velocity. The velocity can\nbe fed directly to `animateDecay` for the fling animation. When we want to slide\nthe offset value back to the original position, we specify the target offset\nvalue of `0f` with the `animateTo` method.\n\n\n```kotlin\nfun Modifier.swipeToDismiss(\n onDismissed: () -\u003e Unit\n): Modifier = composed {\n val offsetX = remember { Animatable(0f) }\n pointerInput(Unit) {\n // Used to calculate fling decay.\n val decay = splineBasedDecay\u003cFloat\u003e(this)\n // Use suspend functions for touch events and the Animatable.\n coroutineScope {\n while (true) {\n val velocityTracker = VelocityTracker()\n // Stop any ongoing animation.\n offsetX.stop()\n awaitPointerEventScope {\n // Detect a touch down event.\n val pointerId = awaitFirstDown().id\n\n horizontalDrag(pointerId) { change -\u003e\n // Update the animation value with touch events.\n launch {\n offsetX.snapTo(\n offsetX.value + change.positionChange().x\n )\n }\n velocityTracker.addPosition(\n change.uptimeMillis,\n change.position\n )\n }\n }\n // No longer receiving touch events. Prepare the animation.\n val velocity = velocityTracker.calculateVelocity().x\n val targetOffsetX = decay.calculateTargetValue(\n offsetX.value,\n velocity\n )\n // The animation stops when it reaches the bounds.\n offsetX.updateBounds(\n lowerBound = -size.width.toFloat(),\n upperBound = size.width.toFloat()\n )\n launch {\n if (targetOffsetX.absoluteValue \u003c= size.width) {\n // Not enough velocity; Slide back.\n offsetX.animateTo(\n targetValue = 0f,\n initialVelocity = velocity\n )\n } else {\n // The element was swiped away.\n offsetX.animateDecay(velocity, decay)\n onDismissed()\n }\n }\n }\n }\n }\n .offset { IntOffset(offsetX.value.roundToInt(), 0) }\n}https://github.com/android/snippets/blob/5673ffc60b614daf028ee936227128eb8c4f9781/compose/snippets/src/main/java/com/example/compose/snippets/animations/AdvancedAnimationSnippets.kt#L94-L152\n```\n\n\u003cbr /\u003e\n\nRecommended for you\n\n- Note: link text is displayed when JavaScript is off\n- [Value-based animations](/develop/ui/compose/animation/value-based)\n- [Drag, swipe, and fling](/develop/ui/compose/touch-input/pointer-input/drag-swipe-fling)\n- [Understand gestures](/develop/ui/compose/touch-input/pointer-input/understand-gestures)"]]