UICollectionView Horizontal Paging not centered
Remove spaces between items. For horizontal scrolling collection view set minimum line spacing to 0. You can do this with interface builder or with method of UICollectionViewDelegateFlowLayout
protocol:
- (CGFloat)collectionView:(UICollectionView *)collectionView
layout:(UICollectionViewLayout *)collectionViewLayout
minimumLineSpacingForSectionAtIndex:(NSInteger)section {
return 0;
}
Another way is making your cell's width less than collectionView's width for a value of horizontal space between items. Then add section insets with left and right insets that equal a half of horizontal space between items. For example, your minimum line spacing is 10:
- (CGFloat)collectionView:(UICollectionView *)collectionView
layout:(UICollectionViewLayout *)collectionViewLayout
minimumLineSpacingForSectionAtIndex:(NSInteger)section {
return 10;
}
- (CGSize)collectionView:(UICollectionView *)collectionView
layout:(UICollectionViewLayout *)collectionViewLayout
sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
return CGSizeMake(collectionView.frame.size.width - 10, collectionView.frame.size.height);
}
- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView
layout:(UICollectionViewLayout *)collectionViewLayout
insetForSectionAtIndex:(NSInteger)section {
return UIEdgeInsetsMake(0, 5, 0, 5);
}
And third way: manipulate collectionView scroll in scrollViewDidEndDecelerating:
method:
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
if (scrollView == self.collectionView) {
CGPoint currentCellOffset = self.collectionView.contentOffset;
currentCellOffset.x += self.collectionView.frame.size.width / 2;
NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint:currentCellOffset];
[self.collectionView scrollToItemAtIndexPath:indexPath
atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally
animated:YES];
}
}
Swift version of @vlad-che accepted answer:
extension GoodsViewController: UICollectionViewDelegateFlowLayout {
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return 10
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
let frameSize = collectionView.frame.size
return CGSize(width: frameSize.width - 10, height: frameSize.height)
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
return UIEdgeInsets(top: 0, left: 5, bottom: 0, right: 5)
}
}
Demo here in Swift 3: https://github.com/damienromito/CollectionViewCustom
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
let pageWidth = Float(itemWidth + itemSpacing)
let targetXContentOffset = Float(targetContentOffset.pointee.x)
let contentWidth = Float(collectionView!.contentSize.width )
var newPage = Float(self.pageControl.currentPage)
if velocity.x == 0 {
newPage = floor( (targetXContentOffset - Float(pageWidth) / 2) / Float(pageWidth)) + 1.0
} else {
newPage = Float(velocity.x > 0 ? self.pageControl.currentPage + 1 : self.pageControl.currentPage - 1)
if newPage < 0 {
newPage = 0
}
if (newPage > contentWidth / pageWidth) {
newPage = ceil(contentWidth / pageWidth) - 1.0
}
}
self.pageControl.currentPage = Int(newPage)
let point = CGPoint (x: CGFloat(newPage * pageWidth), y: targetContentOffset.pointee.y)
targetContentOffset.pointee = point
}
Swift 4:
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
let pageWidth = Float(itemWidth + itemSpacing)
let targetXContentOffset = Float(targetContentOffset.pointee.x)
let contentWidth = Float(collectionView!.contentSize.width )
var newPage = Float(self.pageControl.currentPage)
if velocity.x == 0 {
newPage = floor( (targetXContentOffset - Float(pageWidth) / 2) / Float(pageWidth)) + 1.0
} else {
newPage = Float(velocity.x > 0 ? self.pageControl.currentPage + 1 : self.pageControl.currentPage - 1)
if newPage < 0 {
newPage = 0
}
if (newPage > contentWidth / pageWidth) {
newPage = ceil(contentWidth / pageWidth) - 1.0
}
}
self.pageControl.currentPage = Int(newPage)
let point = CGPoint (x: CGFloat(newPage * pageWidth), y: targetContentOffset.pointee.y)
targetContentOffset.pointee = point
}