OverscrollEffect
- Cmn
interface OverscrollEffect
An OverscrollEffect represents a visual effect that displays when the edges of a scrolling container have been reached with a scroll or fling. To create an instance of the default / currently provided OverscrollFactory, use rememberOverscrollEffect.
To implement, make sure to override node - this has a default implementation for compatibility reasons, but is required for an OverscrollEffect to render.
OverscrollEffect conceptually 'decorates' scroll / fling events: consuming some of the delta or velocity before and/or after the event is consumed by the scrolling container. applyToScroll applies overscroll to a scroll event, and applyToFling applies overscroll to a fling.
Higher level components such as androidx.compose.foundation.lazy.LazyColumn will automatically configure an OverscrollEffect for you. To use a custom OverscrollEffect you first need to provide it with scroll and/or fling events - usually by providing it to a androidx.compose.foundation.gestures.scrollable. Then you can draw the effect on top of the scrolling content using Modifier.overscroll.
import androidx.compose.animation.core.Animatable import androidx.compose.animation.core.spring import androidx.compose.foundation.OverscrollEffect import androidx.compose.foundation.background import androidx.compose.foundation.gestures.Orientation import androidx.compose.foundation.gestures.rememberScrollableState import androidx.compose.foundation.gestures.scrollable import androidx.compose.foundation.layout.Box import androidx.compose.foundation.layout.size import androidx.compose.foundation.overscroll import androidx.compose.material.Text import androidx.compose.runtime.getValue import androidx.compose.runtime.mutableStateOf import androidx.compose.runtime.remember import androidx.compose.runtime.rememberCoroutineScope import androidx.compose.runtime.setValue import androidx.compose.ui.Alignment import androidx.compose.ui.Modifier import androidx.compose.ui.geometry.Offset import androidx.compose.ui.graphics.Color import androidx.compose.ui.input.nestedscroll.NestedScrollSource import androidx.compose.ui.layout.Measurable import androidx.compose.ui.layout.MeasureResult import androidx.compose.ui.layout.MeasureScope import androidx.compose.ui.node.DelegatableNode import androidx.compose.ui.node.LayoutModifierNode import androidx.compose.ui.text.TextStyle import androidx.compose.ui.unit.Constraints import androidx.compose.ui.unit.IntOffset import androidx.compose.ui.unit.Velocity import androidx.compose.ui.unit.dp import androidx.compose.ui.unit.sp // our custom offset overscroll that offset the element it is applied to when we hit the bound // on the scrollable container. class OffsetOverscrollEffect(val scope: CoroutineScope) : OverscrollEffect { private val overscrollOffset = Animatable(0f) override fun applyToScroll( delta: Offset, source: NestedScrollSource, performScroll: (Offset) -> Offset, ): Offset { // in pre scroll we relax the overscroll if needed // relaxation: when we are in progress of the overscroll and user scrolls in the // different direction = substract the overscroll first val sameDirection = sign(delta.y) == sign(overscrollOffset.value) val consumedByPreScroll = if (abs(overscrollOffset.value) > 0.5 && !sameDirection) { val prevOverscrollValue = overscrollOffset.value val newOverscrollValue = overscrollOffset.value + delta.y if (sign(prevOverscrollValue) != sign(newOverscrollValue)) { // sign changed, coerce to start scrolling and exit scope.launch { overscrollOffset.snapTo(0f) } Offset(x = 0f, y = delta.y + prevOverscrollValue) } else { scope.launch { overscrollOffset.snapTo(overscrollOffset.value + delta.y) } delta.copy(x = 0f) } } else { Offset.Zero } val leftForScroll = delta - consumedByPreScroll val consumedByScroll = performScroll(leftForScroll) val overscrollDelta = leftForScroll - consumedByScroll // if it is a drag, not a fling, add the delta left to our over scroll value if (abs(overscrollDelta.y) > 0.5 && source == NestedScrollSource.UserInput) { scope.launch { // multiply by 0.1 for the sake of parallax effect overscrollOffset.snapTo(overscrollOffset.value + overscrollDelta.y * 0.1f) } } return consumedByPreScroll + consumedByScroll } override suspend fun applyToFling( velocity: Velocity, performFling: suspend (Velocity) -> Velocity, ) { val consumed = performFling(velocity) // when the fling happens - we just gradually animate our overscroll to 0 val remaining = velocity - consumed overscrollOffset.animateTo( targetValue = 0f, initialVelocity = remaining.y, animationSpec = spring(), ) } override val isInProgress: Boolean get() = overscrollOffset.value != 0f // Create a LayoutModifierNode that offsets by overscrollOffset.value override val node: DelegatableNode = object : Modifier.Node(), LayoutModifierNode { override fun MeasureScope.measure( measurable: Measurable, constraints: Constraints, ): MeasureResult { val placeable = measurable.measure(constraints) return layout(placeable.width, placeable.height) { val offsetValue = IntOffset(x = 0, y = overscrollOffset.value.roundToInt()) placeable.placeRelativeWithLayer(offsetValue.x, offsetValue.y) } } } } val offset = remember { mutableStateOf(0f) } val scope = rememberCoroutineScope() // Create the overscroll controller val overscroll = remember(scope) { OffsetOverscrollEffect(scope) } // let's build a scrollable that scroll until -512 to 512 val scrollStateRange = (-512f).rangeTo(512f) Box( Modifier.size(150.dp) .scrollable( orientation = Orientation.Vertical, state = rememberScrollableState { delta -> // use the scroll data and indicate how much this element consumed. val oldValue = offset.value // coerce to our range offset.value = (offset.value + delta).coerceIn(scrollStateRange) offset.value - oldValue // indicate that we consumed what's needed }, // pass the overscroll to the scrollable so the data is updated overscrollEffect = overscroll, ) .background(Color.LightGray), contentAlignment = Alignment.Center, ) { Text( offset.value.roundToInt().toString(), style = TextStyle(fontSize = 32.sp), modifier = Modifier // show the overscroll only on the text, not the containers (just for fun) .overscroll(overscroll), ) }
Summary
Public functions | ||
|---|---|---|
suspend Unit | applyToFling(Applies overscroll to | Cmn |
Offset | applyToScroll(Applies overscroll to | Cmn |
Public properties | ||
|---|---|---|
open Modifier | This property is deprecated. This has been replaced with `node`. | Cmn |
Boolean | Whether this OverscrollEffect is currently displaying overscroll. | Cmn |
open DelegatableNode | The | Cmn |
Extension functions | ||
|---|---|---|
OverscrollEffect | Returns a wrapped version of | Cmn |
OverscrollEffect | Returns a wrapped version of | Cmn |
Public functions
applyToFling
suspend fun applyToFling(
velocity: Velocity,
performFling: suspend (Velocity) -> Velocity
): Unit
Applies overscroll to performFling. performFling should represent a fling (the release of a drag or scroll), and returns the amount of Velocity consumed, so in simple cases the amount of overscroll to show should be equal to velocity - performFling(velocity). The OverscrollEffect can optionally consume some Velocity before calling performFling, such as to release any existing tension. The implementation must call performFling exactly once.
For example, assume we want to apply overscroll to a custom component that isn't using androidx.compose.foundation.gestures.scrollable. Here is a simple example of a component using androidx.compose.foundation.gestures.draggable instead:
import androidx.compose.foundation.gestures.Orientation import androidx.compose.foundation.gestures.draggable import androidx.compose.foundation.gestures.rememberDraggableState import androidx.compose.foundation.layout.Box import androidx.compose.foundation.layout.size import androidx.compose.material.Text import androidx.compose.runtime.mutableStateOf import androidx.compose.runtime.remember import androidx.compose.ui.Alignment import androidx.compose.ui.Modifier import androidx.compose.ui.unit.dp var dragPosition by remember { mutableStateOf(0f) } val minPosition = -1000f val maxPosition = 1000f val draggableState = rememberDraggableState { delta -> val newPosition = (dragPosition + delta).coerceIn(minPosition, maxPosition) dragPosition = newPosition } Box( Modifier.size(100.dp).draggable(draggableState, orientation = Orientation.Horizontal), contentAlignment = Alignment.Center, ) { Text("Drag position $dragPosition") }
To apply overscroll, we decorate the existing logic with applyToScroll, and return the amount of delta we have consumed when updating the drag position. We then call applyToFling using the velocity provided by onDragStopped.
import androidx.compose.foundation.OverscrollEffect import androidx.compose.foundation.gestures.Orientation import androidx.compose.foundation.gestures.draggable import androidx.compose.foundation.gestures.rememberDraggableState import androidx.compose.foundation.gestures.scrollable import androidx.compose.foundation.layout.Box import androidx.compose.foundation.layout.size import androidx.compose.foundation.overscroll import androidx.compose.foundation.rememberOverscrollEffect import androidx.compose.material.Text import androidx.compose.runtime.mutableStateOf import androidx.compose.runtime.remember import androidx.compose.ui.Alignment import androidx.compose.ui.Modifier import androidx.compose.ui.geometry.Offset import androidx.compose.ui.input.nestedscroll.NestedScrollSource import androidx.compose.ui.unit.Velocity import androidx.compose.ui.unit.dp var dragPosition by remember { mutableStateOf(0f) } val minPosition = -1000f val maxPosition = 1000f val overscrollEffect = rememberOverscrollEffect() val draggableState = rememberDraggableState { delta -> // Horizontal, so convert the delta to a horizontal offset val deltaAsOffset = Offset(delta, 0f) val performDrag: (Offset) -> Offset = { remainingOffset -> val remainingDelta = remainingOffset.x val newPosition = (dragPosition + remainingDelta).coerceIn(minPosition, maxPosition) // Calculate how much delta we have consumed val consumed = newPosition - dragPosition dragPosition = newPosition // Return how much offset we consumed, so that we can show overscroll for what is left Offset(consumed, 0f) } if (overscrollEffect != null) { // Wrap the original logic inside applyToScroll overscrollEffect.applyToScroll(deltaAsOffset, NestedScrollSource.UserInput, performDrag) } else { performDrag(deltaAsOffset) } } Box( Modifier // Draw overscroll on the box .overscroll(overscrollEffect) .size(100.dp) .draggable( draggableState, orientation = Orientation.Horizontal, onDragStopped = { overscrollEffect?.applyToFling(Velocity(it, 0f)) { velocity -> if (dragPosition == minPosition || dragPosition == maxPosition) { // If we are at the min / max bound, give overscroll all of the velocity Velocity.Zero } else { // If we aren't at the min / max bound, consume all of the velocity so // overscroll won't show. Normally in this case something like // Modifier.scrollable would use the velocity to update the scroll state // with a fling animation, but just do nothing to keep this simpler. velocity } } }, ), contentAlignment = Alignment.Center, ) { Text("Drag position $dragPosition") }
| Parameters | |
|---|---|
velocity: Velocity | total |
performFling: suspend (Velocity) -> Velocity | the |
applyToScroll
fun applyToScroll(
delta: Offset,
source: NestedScrollSource,
performScroll: (Offset) -> Offset
): Offset
Applies overscroll to performScroll. performScroll should represent a drag / scroll, and returns the amount of delta consumed, so in simple cases the amount of overscroll to show should be equal to delta - performScroll(delta). The OverscrollEffect can optionally consume some delta before calling performScroll, such as to release any existing tension. The implementation must call performScroll exactly once. This function should return the sum of all the delta that was consumed during this operation - both by the overscroll and performScroll.
For example, assume we want to apply overscroll to a custom component that isn't using androidx.compose.foundation.gestures.scrollable. Here is a simple example of a component using androidx.compose.foundation.gestures.draggable instead:
import androidx.compose.foundation.gestures.Orientation import androidx.compose.foundation.gestures.draggable import androidx.compose.foundation.gestures.rememberDraggableState import androidx.compose.foundation.layout.Box import androidx.compose.foundation.layout.size import androidx.compose.material.Text import androidx.compose.runtime.mutableStateOf import androidx.compose.runtime.remember import androidx.compose.ui.Alignment import androidx.compose.ui.Modifier import androidx.compose.ui.unit.dp var dragPosition by remember { mutableStateOf(0f) } val minPosition = -1000f val maxPosition = 1000f val draggableState = rememberDraggableState { delta -> val newPosition = (dragPosition + delta).coerceIn(minPosition, maxPosition) dragPosition = newPosition } Box( Modifier.size(100.dp).draggable(draggableState, orientation = Orientation.Horizontal), contentAlignment = Alignment.Center, ) { Text("Drag position $dragPosition") }
To apply overscroll, we need to decorate the existing logic with applyToScroll, and return the amount of delta we have consumed when updating the drag position. Note that we also need to call applyToFling - this is used as an end signal for overscroll so that effects can correctly reset after any animations, when the gesture has stopped.
import androidx.compose.foundation.OverscrollEffect import androidx.compose.foundation.gestures.Orientation import androidx.compose.foundation.gestures.draggable import androidx.compose.foundation.gestures.rememberDraggableState import androidx.compose.foundation.gestures.scrollable import androidx.compose.foundation.layout.Box import androidx.compose.foundation.layout.size import androidx.compose.foundation.overscroll import androidx.compose.foundation.rememberOverscrollEffect import androidx.compose.material.Text import androidx.compose.runtime.mutableStateOf import androidx.compose.runtime.remember import androidx.compose.ui.Alignment import androidx.compose.ui.Modifier import androidx.compose.ui.geometry.Offset import androidx.compose.ui.input.nestedscroll.NestedScrollSource import androidx.compose.ui.unit.Velocity import androidx.compose.ui.unit.dp var dragPosition by remember { mutableStateOf(0f) } val minPosition = -1000f val maxPosition = 1000f val overscrollEffect = rememberOverscrollEffect() val draggableState = rememberDraggableState { delta -> // Horizontal, so convert the delta to a horizontal offset val deltaAsOffset = Offset(delta, 0f) val performDrag: (Offset) -> Offset = { remainingOffset -> val remainingDelta = remainingOffset.x val newPosition = (dragPosition + remainingDelta).coerceIn(minPosition, maxPosition) // Calculate how much delta we have consumed val consumed = newPosition - dragPosition dragPosition = newPosition // Return how much offset we consumed, so that we can show overscroll for what is left Offset(consumed, 0f) } if (overscrollEffect != null) { // Wrap the original logic inside applyToScroll overscrollEffect.applyToScroll(deltaAsOffset, NestedScrollSource.UserInput, performDrag) } else { performDrag(deltaAsOffset) } } Box( Modifier // Draw overscroll on the box .overscroll(overscrollEffect) .size(100.dp) .draggable( draggableState, orientation = Orientation.Horizontal, onDragStopped = { overscrollEffect?.applyToFling(Velocity(it, 0f)) { velocity -> if (dragPosition == minPosition || dragPosition == maxPosition) { // If we are at the min / max bound, give overscroll all of the velocity Velocity.Zero } else { // If we aren't at the min / max bound, consume all of the velocity so // overscroll won't show. Normally in this case something like // Modifier.scrollable would use the velocity to update the scroll state // with a fling animation, but just do nothing to keep this simpler. velocity } } }, ), contentAlignment = Alignment.Center, ) { Text("Drag position $dragPosition") }
| Parameters | |
|---|---|
delta: Offset | total scroll delta available |
source: NestedScrollSource | the source of the delta |
performScroll: (Offset) -> Offset | the scroll action that the overscroll is applied to. The |
| Returns | |
|---|---|
Offset | the delta consumed from |
Public properties
effectModifier
open val effectModifier: Modifier
A Modifier that will draw this OverscrollEffect
This API is deprecated- implementers should instead override node. Callers should use Modifier.overscroll.
isInProgress
val isInProgress: Boolean
Whether this OverscrollEffect is currently displaying overscroll.
| Returns | |
|---|---|
Boolean | true if this OverscrollEffect is currently displaying overscroll |
node
open val node: DelegatableNode
The DelegatableNode that will render this OverscrollEffect and provide any required size or other information to this effect.
In most cases you should use Modifier.overscroll to render this OverscrollEffect, which will internally attach this node to the hierarchy. The node should be attached before applyToScroll or applyToFling is called to ensure correctness.
This property should return a single instance, and can only be attached once, as with other DelegatableNodes.
Extension functions
withoutEventHandling
fun OverscrollEffect.withoutEventHandling(): OverscrollEffect
Returns a wrapped version of this that will not handle any incoming events. This means that calls to OverscrollEffect.applyToScroll / OverscrollEffect.applyToFling will directly execute the provided performScroll / performFling lambdas, without the OverscrollEffect ever seeing the incoming values. OverscrollEffect.node will still be attached, so that overscroll can render.
This can be useful if you want to render an OverscrollEffect in a different component that normally provides events to overscroll, such as a androidx.compose.foundation.lazy.LazyColumn. Use this along with withoutVisualEffect to create two wrapped instances: one that does not handle events, and one that does not draw, so you can ensure that the overscroll effect is only rendered once, and only receives events from one source.
| See also | |
|---|---|
withoutVisualEffect |
withoutVisualEffect
fun OverscrollEffect.withoutVisualEffect(): OverscrollEffect
Returns a wrapped version of this with an empty OverscrollEffect.node. This prevents the overscroll effect from applying any visual effect, but it will still handle events.
This can be used along with withoutEventHandling in cases where you wish to change where overscroll is rendered for a given component. Pass this wrapped instance that doesn't render to the component that handles events (such as androidx.compose.foundation.lazy.LazyColumn) to prevent it from drawing the overscroll effect. Then to separately render the original overscroll effect, you can directly pass it to Modifier.overscroll (since that modifier only renders, and does not handle events). If instead you want to draw the overscroll in another component that handles events, such as a different lazy list, you need to first wrap the original overscroll effect with withoutEventHandling to prevent it from also dispatching events.
import androidx.compose.foundation.OverscrollEffect import androidx.compose.foundation.layout.size import androidx.compose.foundation.lazy.LazyColumn import androidx.compose.foundation.lazy.items import androidx.compose.foundation.lazy.rememberLazyListState import androidx.compose.foundation.overscroll import androidx.compose.foundation.rememberOverscrollEffect import androidx.compose.foundation.withoutVisualEffect import androidx.compose.material.Text import androidx.compose.runtime.remember import androidx.compose.ui.Modifier import androidx.compose.ui.draw.clip import androidx.compose.ui.draw.drawBehind import androidx.compose.ui.geometry.Offset import androidx.compose.ui.graphics.Color import androidx.compose.ui.graphics.RectangleShape import androidx.compose.ui.unit.dp val items = remember { (1..100).toList() } val state = rememberLazyListState() val overscroll = rememberOverscrollEffect() // Create a wrapped version of the above overscroll effect that does not apply a visual effect. // This will be used inside LazyColumn to provide events to overscroll, without letting // LazyColumn render the overscroll effect internally. val overscrollWithoutVisualEffect = overscroll?.withoutVisualEffect() LazyColumn( content = { items(items) { Text("Item $it") } }, state = state, modifier = Modifier.size(300.dp) .clip(RectangleShape) // Manually render the overscroll on top of the lazy list _and_ the 'decorations' we // are // manually drawing, to make sure they will also be included in the overscroll // effect. .overscroll(overscroll) .drawBehind { state.layoutInfo.visibleItemsInfo.drop(1).forEach { info -> val verticalOffset = info.offset.toFloat() drawLine( color = Color.Red, start = Offset(0f, verticalOffset), end = Offset(size.width, verticalOffset), ) } }, // Pass the overscroll effect that does not apply a visual effect inside the LazyList to // receive overscroll events overscrollEffect = overscrollWithoutVisualEffect, )
| See also | |
|---|---|
withoutEventHandling |