| /* |
| * Copyright 2019 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package androidx.compose.material.internal |
| |
| import androidx.compose.animation.core.AnimatedFloat |
| import androidx.compose.animation.core.AnimationClockObservable |
| import androidx.compose.animation.core.AnimationEndReason |
| import androidx.compose.animation.core.AnimationSpec |
| import androidx.compose.animation.core.ExponentialDecay |
| import androidx.compose.animation.core.OnAnimationEnd |
| import androidx.compose.animation.core.Spring |
| import androidx.compose.animation.core.TargetAnimation |
| import androidx.compose.runtime.onCommit |
| import androidx.compose.runtime.remember |
| import androidx.compose.runtime.state |
| import androidx.compose.animation.asDisposableClock |
| import androidx.ui.core.AnimationClockAmbient |
| import androidx.ui.core.Modifier |
| import androidx.ui.core.composed |
| import androidx.ui.core.gesture.scrollorientationlocking.Orientation |
| import androidx.compose.foundation.InteractionState |
| import androidx.compose.foundation.animation.FlingConfig |
| import androidx.compose.foundation.animation.fling |
| import androidx.compose.foundation.gestures.draggable |
| import androidx.compose.ui.util.fastFirstOrNull |
| import androidx.compose.ui.util.lerp |
| import androidx.compose.ui.util.annotation.FloatRange |
| import kotlin.math.sign |
| |
| /** |
| * Enable automatic drag and animation between predefined states. |
| * |
| * This can be used for example in a Switch to enable dragging between two states (true and |
| * false). Additionally, it will animate correctly when the value of the state parameter is changed. |
| * |
| * Additional features compared to [draggable]: |
| * 1. [onNewValue] provides the developer with the new value every time drag or animation (caused |
| * by fling or [state] change) occurs. The developer needs to hold this state on their own |
| * 2. When the anchor is reached, [onStateChange] will be called with state mapped to this anchor |
| * 3. When the anchor is reached and [onStateChange] with corresponding state is called, but |
| * call site didn't update state to the reached one for some reason, |
| * this component performs rollback to the previous (correct) state. |
| * 4. When new [state] is provided, component will be animated to state's anchor |
| * |
| * @param T type with which state is represented |
| * @param state current state to represent Float value with |
| * @param onStateChange callback to update call site's state |
| * @param anchorsToState pairs of anchors to states to map anchors to state and vise versa |
| * @param animationSpec animation which will be used for animations |
| * @param orientation orientation of the drag |
| * @param thresholds the thresholds between anchors that determine which anchor to fling to when |
| * dragging stops, represented as a lambda that takes a pair of anchors and returns a value |
| * between them (note that the order of the anchors matters as it indicates the drag direction) |
| * @param enabled whether or not this Draggable is enabled and should consume events |
| * @param reverseDirection reverse the direction of the scroll, so top to bottom scroll will |
| * behave like bottom to top and left to right will behave like right to left. |
| * @param minValue lower bound for draggable value in this component |
| * @param maxValue upper bound for draggable value in this component |
| * @param onNewValue callback to update state that the developer owns when animation or drag occurs |
| */ |
| // TODO(malkov/tianliu) (figure our how to make it better and make public) |
| internal fun <T> Modifier.stateDraggable( |
| state: T, |
| onStateChange: (T) -> Unit, |
| anchorsToState: List<Pair<Float, T>>, |
| animationSpec: AnimationSpec<Float>, |
| orientation: Orientation, |
| thresholds: (Float, Float) -> Float = fractionalThresholds(0.5f), |
| enabled: Boolean = true, |
| reverseDirection: Boolean = false, |
| minValue: Float = Float.MIN_VALUE, |
| maxValue: Float = Float.MAX_VALUE, |
| interactionState: InteractionState? = null, |
| onNewValue: (Float) -> Unit |
| ) = composed { |
| val forceAnimationCheck = state { true } |
| |
| val anchors = remember(anchorsToState) { anchorsToState.map { it.first } } |
| val currentValue = anchorsToState.fastFirstOrNull { it.second == state }!!.first |
| |
| val onAnimationEnd: OnAnimationEnd = { reason, finalValue, _ -> |
| if (reason != AnimationEndReason.Interrupted) { |
| val newState = anchorsToState.firstOrNull { it.first == finalValue }?.second |
| if (newState != null && newState != state) { |
| onStateChange(newState) |
| forceAnimationCheck.value = !forceAnimationCheck.value |
| } |
| } |
| } |
| val flingConfig = FlingConfig( |
| decayAnimation = ExponentialDecay(), |
| adjustTarget = { target -> |
| // Find the two anchors the target lies between. |
| val a = anchors.filter { it <= target }.maxOrNull() |
| val b = anchors.filter { it >= target }.minOrNull() |
| // Compute which anchor to fling to. |
| val adjusted: Float = |
| if (a == null && b == null) { |
| // There are no anchors, so return the target unchanged. |
| target |
| } else if (a == null) { |
| // The target lies below the anchors, so return the first anchor (b). |
| b!! |
| } else if (b == null) { |
| // The target lies above the anchors, so return the last anchor (b). |
| a |
| } else if (a == b) { |
| // The target is equal to one of the anchors, so return the target unchanged. |
| target |
| } else { |
| // The target lies strictly between the two anchors a and b. |
| // Compute the threshold between a and b based on the drag direction. |
| val threshold = if (currentValue <= a) { |
| thresholds(a, b) |
| } else { |
| thresholds(b, a) |
| } |
| require(threshold >= a && threshold <= b) { |
| "Invalid threshold $threshold between anchors $a and $b." |
| } |
| if (target < threshold) a else b |
| } |
| TargetAnimation(adjusted, animationSpec) |
| } |
| ) |
| val clock = AnimationClockAmbient.current.asDisposableClock() |
| val position = remember(clock) { |
| onNewValue(currentValue) |
| NotificationBasedAnimatedFloat(currentValue, clock, onNewValue) |
| } |
| position.onNewValue = onNewValue |
| position.setBounds(minValue, maxValue) |
| |
| // This state is to force this component to be recomposed and trigger onCommit below |
| // This is needed to stay in sync with drag state that caller side holds |
| onCommit(currentValue, forceAnimationCheck.value) { |
| position.animateTo(currentValue, animationSpec) |
| } |
| Modifier.draggable( |
| orientation = orientation, |
| enabled = enabled, |
| reverseDirection = reverseDirection, |
| startDragImmediately = position.isRunning, |
| interactionState = interactionState, |
| onDragStopped = { position.fling(it, flingConfig, onAnimationEnd) } |
| ) { delta -> |
| position.snapTo(position.value + delta) |
| } |
| } |
| |
| /** |
| * Fixed anchors thresholds. Each threshold will be at an [offset] away from the first anchor. |
| */ |
| internal fun fixedThresholds(offset: Float): (Float, Float) -> Float = |
| { fromAnchor, toAnchor -> fromAnchor + offset * sign(toAnchor - fromAnchor) } |
| |
| /** |
| * Fractional thresholds. Each threshold will be at a [fraction] of the way between the two anchors. |
| */ |
| internal fun fractionalThresholds( |
| @FloatRange(from = 0.0, to = 1.0) fraction: Float |
| ): (Float, Float) -> Float = { fromAnchor, toAnchor -> lerp(fromAnchor, toAnchor, fraction) } |
| |
| private class NotificationBasedAnimatedFloat( |
| initial: Float, |
| clock: AnimationClockObservable, |
| internal var onNewValue: (Float) -> Unit |
| ) : AnimatedFloat(clock, Spring.DefaultDisplacementThreshold) { |
| |
| override var value = initial |
| set(value) { |
| onNewValue(value) |
| field = value |
| } |
| } |