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113 lines
3.6 KiB
Objective-C
113 lines
3.6 KiB
Objective-C
//
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// ASPagerFlowLayout.m
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// AsyncDisplayKit
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//
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// Created by Levi McCallum on 2/12/16.
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//
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// Copyright (c) 2014-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under the BSD-style license found in the
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// LICENSE file in the root directory of this source tree. An additional grant
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// of patent rights can be found in the PATENTS file in the same directory.
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//
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#import <AsyncDisplayKit/ASPagerFlowLayout.h>
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#import <AsyncDisplayKit/ASCellNode.h>
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#import <AsyncDisplayKit/ASCollectionView.h>
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@interface ASPagerFlowLayout () {
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__weak ASCellNode *_currentCellNode;
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}
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@end
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@implementation ASPagerFlowLayout
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- (ASCollectionView *)asCollectionView
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{
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// Dynamic cast is too slow and not worth it.
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return (ASCollectionView *)self.collectionView;
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}
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- (void)prepareLayout
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{
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[super prepareLayout];
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if (_currentCellNode == nil) {
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[self _updateCurrentNode];
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}
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}
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- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset
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{
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// Don't mess around if the user is interacting with the page node. Although if just a rotation happened we should
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// try to use the current index path to not end up setting the target content offset to something in between pages
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if (!self.collectionView.decelerating && !self.collectionView.tracking) {
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NSIndexPath *indexPath = [self.asCollectionView indexPathForNode:_currentCellNode];
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if (indexPath) {
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return [self _targetContentOffsetForItemAtIndexPath:indexPath proposedContentOffset:proposedContentOffset];
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}
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}
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return [super targetContentOffsetForProposedContentOffset:proposedContentOffset];
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}
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- (CGPoint)_targetContentOffsetForItemAtIndexPath:(NSIndexPath *)indexPath proposedContentOffset:(CGPoint)proposedContentOffset
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{
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if ([self _dataSourceIsEmpty]) {
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return proposedContentOffset;
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}
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UICollectionViewLayoutAttributes *attributes = [self layoutAttributesForItemAtIndexPath:indexPath];
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if (attributes == nil) {
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return proposedContentOffset;
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}
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CGFloat xOffset = (CGRectGetWidth(self.collectionView.bounds) - CGRectGetWidth(attributes.frame)) / 2.0;
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return CGPointMake(attributes.frame.origin.x - xOffset, proposedContentOffset.y);
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}
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- (BOOL)_dataSourceIsEmpty
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{
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return ([self.collectionView numberOfSections] == 0 ||
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[self.collectionView numberOfItemsInSection:0] == 0);
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}
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- (void)_updateCurrentNode
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{
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// Never change node during an animated bounds change (rotation)
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// NOTE! Listening for -prepareForAnimatedBoundsChange and -finalizeAnimatedBoundsChange
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// isn't sufficient here! It's broken!
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NSArray *animKeys = self.collectionView.layer.animationKeys;
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for (NSString *key in animKeys) {
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if ([key hasPrefix:@"bounds"]) {
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return;
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}
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}
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CGRect bounds = self.collectionView.bounds;
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CGRect rect = CGRectMake(CGRectGetMidX(bounds), CGRectGetMidY(bounds), 1, 1);
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NSIndexPath *indexPath = [self layoutAttributesForElementsInRect:rect].firstObject.indexPath;
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if (indexPath) {
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ASCellNode *node = [self.asCollectionView nodeForItemAtIndexPath:indexPath];
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if (node) {
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_currentCellNode = node;
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}
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}
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}
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- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
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{
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[self _updateCurrentNode];
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return [super shouldInvalidateLayoutForBoundsChange:newBounds];
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}
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- (UICollectionViewLayoutInvalidationContext *)invalidationContextForBoundsChange:(CGRect)newBounds
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{
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UICollectionViewFlowLayoutInvalidationContext *ctx = (UICollectionViewFlowLayoutInvalidationContext *)[super invalidationContextForBoundsChange:newBounds];
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ctx.invalidateFlowLayoutDelegateMetrics = YES;
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ctx.invalidateFlowLayoutAttributes = YES;
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return ctx;
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}
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@end
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