I have a vertical UICollectionView
with each cell taking up the entire self.view.frame
I can easily swipe upwards to page to the next cell, but I would like to do the same thing with the press of a button.
I've tried using:
- (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated
And:
- (void)scrollRectToVisible:(CGRect)rect animated:(BOOL)animated
They work but they temporarily "White-Out" the currentCell to present the nextCell, while the swiping shows both cells during the transition.
Ideally I would like to use:
- (void)scrollToItemAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UICollectionViewScrollPosition)scrollPosition animated:(BOOL)animated
But I don't know how to access the nextCell's indexPath
...
I've tried:
NSIndexPath *nextIndexPath = [_collectionView indexPathForItemAtPoint:CGPointMake(25, (_collectionView.frame.size.height-25)*(_currentIndexRowForCellOnScreen+1))];
Where _currentIndexRowForCellOnScreen
is the indexPath.row
of the UICollectionView
's first appearance on screen in:
- (UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
But when I put it into:
- (NSIndexPath *)indexPathForCell:(UICollectionViewCell *)cell
it returns NULL after the first Cell, and does not animate....
Any direction would be greatly appreciated. Thank you for your time.
Assuming your collectionView contains only 1 section, and given that each item occupies the whole frame then you could do something like this;
NSArray *visibleItems = [self.collectionView indexPathsForVisibleItems];
NSIndexPath *currentItem = [visibleItems objectAtIndex:0];
NSIndexPath *nextItem = [NSIndexPath indexPathForItem:currentItem.item + 1 inSection:currentItem.section];
[self.collectionView scrollToItemAtIndexPath:nextItem atScrollPosition:UICollectionViewScrollPositionTop animated:YES];
By far this is the best approach i have encountered, the trick is to scroll to the frame which is containing next objects. Please refer the code
@IBAction func actionPreviousFriends(_ sender: Any) {
let collectionBounds = self.collectionView.bounds
let contentOffset = CGFloat(floor(self.collectionView.contentOffset.x - collectionBounds.size.width))
self.moveToFrame(contentOffset: contentOffset)
}
/* -------------- display next friends action ----------------*/
@IBAction func actionNextFriends(_ sender: Any) {
let collectionBounds = self.collectionView.bounds
let contentOffset = CGFloat(floor(self.collectionView.contentOffset.x + collectionBounds.size.width))
self.moveToFrame(contentOffset: contentOffset)
}
func moveToFrame(contentOffset : CGFloat) {
let frame: CGRect = CGRect(x : contentOffset ,y : self.collectionView.contentOffset.y ,width : self.collectionView.frame.width,height : self.collectionView.frame.height)
self.collectionView.scrollRectToVisible(frame, animated: true)
}
Here are the Swift versions
Swift 2
let visibleItems: NSArray = self.collectionView.indexPathsForVisibleItems()
let currentItem: NSIndexPath = visibleItems.objectAtIndex(0) as! NSIndexPath
let nextItem: NSIndexPath = NSIndexPath(forRow: currentItem.item + 1, inSection: 0)
self.collectionView.scrollToItemAtIndexPath(nextItem, atScrollPosition: .Top, animated: true)
Swift 3, 4, 5
let visibleItems: NSArray = self.collectionView.indexPathsForVisibleItems as NSArray
let currentItem: IndexPath = visibleItems.object(at: 0) as! IndexPath
let nextItem: IndexPath = IndexPath(item: currentItem.item + 1, section: 0)
self.collectionView.scrollToItem(at: nextItem, at: .top, animated: true)
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