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ricky
18d805f523
* [RTL/Batching] Make ASDisplayShouldFetchBatchForScrollView aware of flipped CV layouts UICollectionViewLayout has a property called `flipsHorizontallyInOppositeLayoutDirection`. If this is set to `YES` then a RTL collectionView’s contentOffset behaves like it does in LTR. In other words, the first item is at contentOffset 0. In this case, the existing logic for `ASDisplayShouldFetchBatchForScrollView` works in RTL. If you don’t override `flipsHorizontallyInOppositeLayoutDirection` to be `YES`, then it means that in RTL languages the first item in your collectionView will actually be at x offset `collectionView.contentSize.width - collectionView.frame.size.width`. As you scroll to the right, the content offset will decrease until you reach the end of the data at a content offset of 0,0. In this case, `ASDisplayShouldFetchBatchForScrollView` needs to know that you are in RTL and the layout is not flipped. It can then use the contentOffset as the `remainingDistance` to determine when to fetch. * fix indentation * assert that we are on main when accessing CV layout
109 lines
4.6 KiB
Plaintext
109 lines
4.6 KiB
Plaintext
//
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// ASBatchFetching.mm
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// Texture
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//
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// Copyright (c) Facebook, Inc. and its affiliates. All rights reserved.
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// Changes after 4/13/2017 are: Copyright (c) Pinterest, Inc. All rights reserved.
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// Licensed under Apache 2.0: http://www.apache.org/licenses/LICENSE-2.0
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//
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#import <AsyncDisplayKit/ASBatchFetching.h>
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#import <AsyncDisplayKit/ASBatchContext.h>
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#import <AsyncDisplayKit/ASBatchFetchingDelegate.h>
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BOOL ASDisplayShouldFetchBatchForScrollView(UIScrollView<ASBatchFetchingScrollView> *scrollView,
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ASScrollDirection scrollDirection,
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ASScrollDirection scrollableDirections,
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CGPoint contentOffset,
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CGPoint velocity,
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BOOL flipsHorizontallyInOppositeLayoutDirection)
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{
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// Don't fetch if the scroll view does not allow
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if (![scrollView canBatchFetch]) {
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return NO;
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}
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// Check if we should batch fetch
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ASBatchContext *context = scrollView.batchContext;
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CGRect bounds = scrollView.bounds;
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CGSize contentSize = scrollView.contentSize;
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CGFloat leadingScreens = scrollView.leadingScreensForBatching;
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id<ASBatchFetchingDelegate> delegate = scrollView.batchFetchingDelegate;
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BOOL visible = (scrollView.window != nil);
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BOOL shouldRenderRTLLayout = [UIView userInterfaceLayoutDirectionForSemanticContentAttribute:scrollView.semanticContentAttribute] == UIUserInterfaceLayoutDirectionRightToLeft;
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return ASDisplayShouldFetchBatchForContext(context, scrollDirection, scrollableDirections, bounds, contentSize, contentOffset, leadingScreens, visible, shouldRenderRTLLayout, velocity, flipsHorizontallyInOppositeLayoutDirection, delegate);
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}
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BOOL ASDisplayShouldFetchBatchForContext(ASBatchContext *context,
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ASScrollDirection scrollDirection,
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ASScrollDirection scrollableDirections,
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CGRect bounds,
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CGSize contentSize,
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CGPoint targetOffset,
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CGFloat leadingScreens,
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BOOL visible,
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BOOL shouldRenderRTLLayout,
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CGPoint velocity,
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BOOL flipsHorizontallyInOppositeLayoutDirection,
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id<ASBatchFetchingDelegate> delegate)
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{
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// Do not allow fetching if a batch is already in-flight and hasn't been completed or cancelled
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if ([context isFetching]) {
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return NO;
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}
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// No fetching for null states
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if (leadingScreens <= 0.0 || CGRectIsEmpty(bounds)) {
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return NO;
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}
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CGFloat viewLength, offset, contentLength, velocityLength;
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if (ASScrollDirectionContainsVerticalDirection(scrollableDirections)) {
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viewLength = bounds.size.height;
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offset = targetOffset.y;
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contentLength = contentSize.height;
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velocityLength = velocity.y;
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} else { // horizontal / right
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viewLength = bounds.size.width;
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offset = targetOffset.x;
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contentLength = contentSize.width;
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velocityLength = velocity.x;
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}
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BOOL hasSmallContent = contentLength < viewLength;
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if (hasSmallContent) {
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return YES;
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}
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// If we are not visible, but we do have enough content to fill visible area,
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// don't batch fetch.
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if (visible == NO) {
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return NO;
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}
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// If they are scrolling toward the head of content, don't batch fetch.
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BOOL isScrollingTowardHead = (ASScrollDirectionContainsUp(scrollDirection) || (shouldRenderRTLLayout ? ASScrollDirectionContainsRight(scrollDirection) : ASScrollDirectionContainsLeft(scrollDirection)));
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if (isScrollingTowardHead) {
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return NO;
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}
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CGFloat triggerDistance = viewLength * leadingScreens;
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CGFloat remainingDistance = 0;
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if (!flipsHorizontallyInOppositeLayoutDirection && shouldRenderRTLLayout && ASScrollDirectionContainsHorizontalDirection(scrollableDirections)) {
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remainingDistance = offset;
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} else {
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remainingDistance = contentLength - viewLength - offset;
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}
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BOOL result = remainingDistance <= triggerDistance;
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if (delegate != nil && velocityLength > 0.0) {
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// Don't need to get absolute value of remaining time
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// because both remainingDistance and velocityLength are positive when scrolling toward tail
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NSTimeInterval remainingTime = remainingDistance / (velocityLength * 1000);
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result = [delegate shouldFetchBatchWithRemainingTime:remainingTime hint:result];
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}
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return result;
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}
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