Horizontal reordering of UICollectionView cells - ios

Question

I've got a UICollectionView with horizontal scrolling. Each cell corresponds to a object (a currency code) in an array. What I would like is to be able to reorder cells via a drag and drop gesture.
I found a tutorial for UITableView and tried it but when I hold and drag a cell it only moves vertically and doesn't scroll when I move my finger to the edge of the screen. Here is a gif.
What I want to happen is for the cell to move horizontally, instead of vertically, and for the collection view to scroll when the edge of the screen is reached. How would I achieve this?
This is what I have now:
UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc] initWithTarget: self action: #selector(longPressGestureRecognised:)];
[self.collectionView addGestureRecognizer: longPress];
-(IBAction) longPressGestureRecognised:(id)sender
{
UILongPressGestureRecognizer *longPress = (UILongPressGestureRecognizer *)sender;
UIGestureRecognizerState state = longPress.state;
CGPoint location = [longPress locationInView: self.collectionView];
NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint: location];
static UIView *snapshot = nil;
static NSIndexPath *sourceIndexPath = nil;
switch (state) {
case UIGestureRecognizerStateBegan: {
if (indexPath) {
sourceIndexPath = indexPath;
UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath: indexPath];
// Take a snapshot of the selected item using helper method.
snapshot = [self customSnapshotFromView: cell];
// Add the snapshot as subview, centered at cell's centre.
__block CGPoint centre = cell.center;
snapshot.center = centre;
snapshot.alpha = 0.0;
[self.collectionView addSubview: snapshot];
[UIView animateWithDuration: 0.25 animations:^{
// Offset for gesture location.
centre.y = location.y;
snapshot.center = centre;
snapshot.transform = CGAffineTransformMakeScale(1.05, 1.05);
snapshot.alpha = 0.98;
// Fade out.
cell.alpha = 0.0;
} completion: ^(BOOL finished) {
cell.hidden = YES;
}];
}
break;
}
case UIGestureRecognizerStateChanged: {
CGPoint centre = snapshot.center;
centre.y = location.y;
snapshot.center = centre;
// Is destination valid and is it different from source?
if (indexPath && ![indexPath isEqual: sourceIndexPath]) {
// Update data source.
[currencyArray exchangeObjectAtIndex: indexPath.item withObjectAtIndex:sourceIndexPath.item];
// Move the items.
[self.collectionView moveItemAtIndexPath: sourceIndexPath toIndexPath: indexPath];
// And update source so it is in sync with UI changes.
sourceIndexPath = indexPath;
}
break;
}
default: {
// Clean up.
UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath: sourceIndexPath];
cell.hidden = NO;
cell.alpha = 0.0;
[UIView animateWithDuration: 0.25 animations: ^{
snapshot.center = cell.center;
snapshot.transform = CGAffineTransformIdentity;
snapshot.alpha = 0.0;
// Undo fade out.
cell.alpha = 1.0;
}completion: ^(BOOL finished) {
sourceIndexPath = nil;
[snapshot removeFromSuperview];
snapshot = nil;
}];
break;
}
}
}
-(UIView *) customSnapshotFromView:(UIView *)inputView
{
// Make an image from the input view.
UIGraphicsBeginImageContextWithOptions(inputView.bounds.size, NO, 0);
[inputView.layer renderInContext: UIGraphicsGetCurrentContext()];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
// Create an image view.
UIView *snapshot = [[UIImageView alloc] initWithImage: image];
snapshot.layer.masksToBounds = NO;
snapshot.layer.cornerRadius = 0.0;
snapshot.layer.shadowOffset = CGSizeMake(-5.0, 0.0);
snapshot.layer.shadowRadius = 5.0;
snapshot.layer.shadowOpacity = 0.4;
return snapshot;
}
EDIT:
I've figured it out. Here is the code:
UILongPressGestureRecognizer *longPress = [[UILongPressGestureRecognizer alloc] initWithTarget: self action: #selector(handleLongGesture:)];
[self.collectionView addGestureRecognizer: longPress];
-(IBAction) handleLongGesture: (id)sender {
UILongPressGestureRecognizer *longPress = (UILongPressGestureRecognizer *)sender;
CGPoint location = [longPress locationInView: self.collectionView];
NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint: location];
switch (longPress.state) {
case UIGestureRecognizerStateBegan:
[self.collectionView beginInteractiveMovementForItemAtIndexPath: indexPath];
NSLog(#"Gesture began");
break;
case UIGestureRecognizerStateChanged:
[self.collectionView updateInteractiveMovementTargetPosition: [longPress locationInView: longPress.view]];
NSLog(#"Gesture state changed");
break;
case UIGestureRecognizerStateEnded:
[self.collectionView endInteractiveMovement];
NSLog(#"Gesture state ended");
break;
default:
[self.collectionView cancelInteractiveMovement];
NSLog(#"Gesture cancelled");
break;
}
}

Answer 1

in UIGestureRecognizerStateChanged:
change this line of code
CGPoint centre = snapshot.center;
centre.x = location.x;
snapshot.center = centre;
centre.y returns y axis dragging
change it to centre.x for x axis dragging