Created
October 2, 2015 22:08
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An implementation of twitter suggested app side-swiping
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- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset { | |
targetContentOffset->x = [self targetOffsetX:targetContentOffset->x inCollectionView:(UICollectionView *)scrollView velocity:velocity]; | |
} | |
- (CGFloat)targetOffsetX:(CGFloat)offsetX inCollectionView:(UICollectionView *)collectionView velocity:(CGPoint)velocity { | |
if (![collectionView isKindOfClass:[UICollectionView class]]) { | |
return offsetX; | |
} | |
NSInteger index = [self indexForScrollView:collectionView targetOffsetX:offsetX velocity:velocity]; | |
UICollectionViewCell *cell = [collectionView cellForItemAtIndexPath:[NSIndexPath indexPathForRow:index inSection:0]]; | |
return (index == 0) ? 0 : cell.frame.origin.x - (collectionView.frame.size.width - cell.frame.size.width)/2 ; | |
} | |
#define kDragVelocityDampener .85 | |
- (NSInteger)indexForScrollView:(UICollectionView *)collectionView targetOffsetX:(CGFloat)offsetX velocity:(CGPoint)velocity { | |
NSInteger returnIndex = [self indexOfOffset:offsetX collectionView:collectionView velocity:velocity]; | |
CGFloat originOfPan =[collectionView.panGestureRecognizer translationInView:self.view].x + collectionView.contentOffset.x; | |
NSInteger origIndex = [self indexOfOffset:originOfPan collectionView:collectionView velocity:velocity]; | |
//Note: as the width of the cell gets much smaller than the width of the collection view, this becomes jerky. | |
if (labs(returnIndex - origIndex)> 1) { | |
return origIndex + ((velocity.x > 0) ? 1 : - 1); | |
} | |
return returnIndex; | |
} | |
- (NSInteger)indexOfOffset:(CGFloat)xOffset collectionView:(UICollectionView *)collectionView velocity:(CGPoint)velocity { | |
if (xOffset == 0) { | |
return 0; | |
} else { | |
CGFloat changeX = fabs(xOffset - collectionView.contentOffset.x)*kDragVelocityDampener;; | |
CGFloat width = [[collectionView visibleCells].firstObject frame].size.width; | |
return (velocity.x >= 0.f) ? ceil((xOffset - changeX)/width) : floor((xOffset + changeX)/width); | |
} | |
} |
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No external state needed. one card swiped at a time.