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lib/java/com/google/android/material/carousel/CarouselSnapHelper.java
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| /* | ||
| * Copyright 2023 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 | ||
| * | ||
| * https://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 com.google.android.material.carousel; | ||
|
|
||
| import android.graphics.PointF; | ||
| import androidx.recyclerview.widget.RecyclerView; | ||
| import androidx.recyclerview.widget.RecyclerView.LayoutManager; | ||
| import androidx.recyclerview.widget.SnapHelper; | ||
| import android.view.View; | ||
| import androidx.annotation.NonNull; | ||
| import androidx.annotation.Nullable; | ||
|
|
||
| /** | ||
| * Implementation of the {@link SnapHelper} that supports snapping items to the carousel keylines | ||
| * according to the strategy. | ||
| */ | ||
| public class CarouselSnapHelper extends SnapHelper { | ||
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|
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| private final boolean disableFling; | ||
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| public CarouselSnapHelper() { | ||
| this(true); | ||
| } | ||
|
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| public CarouselSnapHelper(boolean disableFling) { | ||
| this.disableFling = disableFling; | ||
| } | ||
|
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| @Nullable | ||
| @Override | ||
| public int[] calculateDistanceToFinalSnap( | ||
| @NonNull LayoutManager layoutManager, @NonNull View view) { | ||
| // If the layout manager is not a CarouselLayoutManager, we return with a zero offset | ||
| // as there are no keylines to snap to. | ||
| if (!(layoutManager instanceof CarouselLayoutManager)) { | ||
| return new int[] {0, 0}; | ||
| } | ||
|
|
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| int offset = 0; | ||
| if (layoutManager.canScrollHorizontally()) { | ||
| offset = distanceToFirstFocalKeyline(view, (CarouselLayoutManager) layoutManager); | ||
| } | ||
| // TODO(b/279088745): Implement snap helper for vertical scrolling. | ||
| return new int[] {offset, 0}; | ||
| } | ||
|
|
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| private int distanceToFirstFocalKeyline( | ||
| @NonNull View targetView, CarouselLayoutManager layoutManager) { | ||
| return layoutManager.getOffsetToScrollToPosition(layoutManager.getPosition(targetView)); | ||
| } | ||
|
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| @Nullable | ||
| @Override | ||
| public View findSnapView(LayoutManager layoutManager) { | ||
| // TODO(b/279088745): Implement snap helper for vertical scrolling. | ||
| if (layoutManager.canScrollHorizontally()) { | ||
| return findViewNearestFirstKeyline(layoutManager); | ||
| } | ||
| return null; | ||
| } | ||
|
|
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| /** | ||
| * Return the child view that is currently closest to the first focal keyline. | ||
| * | ||
| * @param layoutManager The {@link LayoutManager} associated with the attached {@link | ||
| * RecyclerView}. | ||
| * @return the child view that is currently closest to the first focal keyline. | ||
| */ | ||
| @Nullable | ||
| private View findViewNearestFirstKeyline(LayoutManager layoutManager) { | ||
| int childCount = layoutManager.getChildCount(); | ||
| if (childCount == 0 || !(layoutManager instanceof CarouselLayoutManager)) { | ||
| return null; | ||
| } | ||
| View closestChild = null; | ||
| int absClosest = Integer.MAX_VALUE; | ||
|
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| CarouselLayoutManager carouselLayoutManager = (CarouselLayoutManager) layoutManager; | ||
| for (int i = 0; i < childCount; i++) { | ||
| final View child = layoutManager.getChildAt(i); | ||
| final int position = layoutManager.getPosition(child); | ||
| final int offset = | ||
| Math.abs(carouselLayoutManager.getOffsetToScrollToPosition(position)); | ||
|
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| // If child center is closer than previous closest, set it as closest | ||
| if (offset < absClosest) { | ||
| absClosest = offset; | ||
| closestChild = child; | ||
| } | ||
| } | ||
| return closestChild; | ||
| } | ||
|
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| @Override | ||
| public int findTargetSnapPosition(LayoutManager layoutManager, int velocityX, int velocityY) { | ||
| if (!disableFling) { | ||
| return RecyclerView.NO_POSITION; | ||
| } | ||
|
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| final int itemCount = layoutManager.getItemCount(); | ||
| if (itemCount == 0) { | ||
| return RecyclerView.NO_POSITION; | ||
| } | ||
|
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| // A child that is exactly centered on the first focal keyline is eligible | ||
| // for both before and after | ||
| View closestChildBeforeKeyline = null; | ||
| int distanceBefore = Integer.MIN_VALUE; | ||
| View closestChildAfterKeyline = null; | ||
| int distanceAfter = Integer.MAX_VALUE; | ||
|
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| // Find the first view before the first focal keyline, and the first view after it | ||
| final int childCount = layoutManager.getChildCount(); | ||
| for (int i = 0; i < childCount; i++) { | ||
| final View child = layoutManager.getChildAt(i); | ||
| if (child == null) { | ||
| continue; | ||
| } | ||
| final int distance = | ||
| distanceToFirstFocalKeyline(child, (CarouselLayoutManager) layoutManager); | ||
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| if (distance <= 0 && distance > distanceBefore) { | ||
| // Child is before the keyline and closer then the previous best | ||
| distanceBefore = distance; | ||
| closestChildBeforeKeyline = child; | ||
| } | ||
| if (distance >= 0 && distance < distanceAfter) { | ||
| // Child is after the keyline and closer then the previous best | ||
| distanceAfter = distance; | ||
| closestChildAfterKeyline = child; | ||
| } | ||
| } | ||
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| // Return the position of the closest child from the first focal keyline, in the direction of | ||
| // the fling | ||
| final boolean forwardDirection = isForwardFling(layoutManager, velocityX, velocityY); | ||
| if (forwardDirection && closestChildAfterKeyline != null) { | ||
| return layoutManager.getPosition(closestChildAfterKeyline); | ||
| } else if (!forwardDirection && closestChildBeforeKeyline != null) { | ||
| return layoutManager.getPosition(closestChildBeforeKeyline); | ||
| } | ||
|
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| // There is no child in the direction of the fling (eg. start/end of list). | ||
| // Extrapolate from the child that is visible to get the position of the view to | ||
| // snap to. | ||
| View visibleView = forwardDirection ? closestChildBeforeKeyline : closestChildAfterKeyline; | ||
| if (visibleView == null) { | ||
| return RecyclerView.NO_POSITION; | ||
| } | ||
| int visiblePosition = layoutManager.getPosition(visibleView); | ||
| int snapToPosition = | ||
| visiblePosition + (isReverseLayout(layoutManager) == forwardDirection ? -1 : 1); | ||
|
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| if (snapToPosition < 0 || snapToPosition >= itemCount) { | ||
| return RecyclerView.NO_POSITION; | ||
| } | ||
| return snapToPosition; | ||
| } | ||
|
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| private boolean isForwardFling( | ||
| RecyclerView.LayoutManager layoutManager, int velocityX, int velocityY) { | ||
| if (layoutManager.canScrollHorizontally()) { | ||
| return velocityX > 0; | ||
| } else { | ||
| return velocityY > 0; | ||
| } | ||
| } | ||
|
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| // Calculates the direction of the layout based on the direction of the scroll vector when | ||
| // scrolling to the end of the list. This is not equivalent to `isRtl` because the recyclerview | ||
| // layout manager may set `reverseLayout`. | ||
| private boolean isReverseLayout(RecyclerView.LayoutManager layoutManager) { | ||
| final int itemCount = layoutManager.getItemCount(); | ||
| if ((layoutManager instanceof RecyclerView.SmoothScroller.ScrollVectorProvider)) { | ||
| RecyclerView.SmoothScroller.ScrollVectorProvider vectorProvider = | ||
| (RecyclerView.SmoothScroller.ScrollVectorProvider) layoutManager; | ||
| PointF vectorForEnd = vectorProvider.computeScrollVectorForPosition(itemCount - 1); | ||
| if (vectorForEnd != null) { | ||
| return vectorForEnd.x < 0 || vectorForEnd.y < 0; | ||
| } | ||
| } | ||
| return false; | ||
| } | ||
| } |
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