Hashem Aboonajmi Hashem Aboonajmi - 1 month ago 11
Objective-C Question

Transforming UICollectionViewCell causes touch events not be captured

Im trying to create a horizontal collection view by subclassing UICollectionViewFlowLayout.
which the center cell be scaled a little more to be focused on the view.

see the screen shot:

enter image description here

but UICollectionViewCell doesn't capture touch events. I mean when I tap on the cell the delegate method

- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath
won't called.
but when I remove the scale transform from the cell, the above method called!

#import "CoverFlowLayout.h"

static const CGFloat kMaxDistancePercentage = 0.3f;
static const CGFloat kMaxRotation = (CGFloat)(50.0 * (M_PI / 180.0));
static const CGFloat kMaxZoom = 0.1f;

@implementation CoverFlowLayout

- (id)init {
if ((self = [super init])) {
self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
self.minimumLineSpacing = 10000.0f; }
return self;
}

- (NSArray*)layoutAttributesForElementsInRect:(CGRect)rect {

// 1
CGRect visibleRect =
(CGRect){.origin = self.collectionView.contentOffset,
.size = self.collectionView.bounds.size};
CGFloat maxDistance =
visibleRect.size.width * kMaxDistancePercentage;
// 2
NSArray *array =
[super layoutAttributesForElementsInRect:rect];
for (UICollectionViewLayoutAttributes *attributes in array) {
// 3
CGFloat distance =
CGRectGetMidX(visibleRect) - attributes.center.x;
// 4
CGFloat normalizedDistance = distance / maxDistance;
normalizedDistance = MIN(normalizedDistance, 1.0f);
normalizedDistance = MAX(normalizedDistance, -1.0f);
// 5
CGFloat rotation = normalizedDistance * kMaxRotation;
CGFloat zoom = 1.0f + ((1.0f - ABS(normalizedDistance)) * kMaxZoom);
// 6
CATransform3D transform = CATransform3DIdentity;
transform.m34 = 1.0 / -1000.0;
//transform = CATransform3DRotate(transform,
// rotation, 0.0f, 1.0f, 0.0f);

transform = CATransform3DScale(transform, zoom, zoom, 0.0f);
attributes.transform3D = transform;
}
// 7
return array;
}

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {
return YES;
}

- (CGPoint)targetContentOffsetForProposedContentOffset: (CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity
{
// 1
CGFloat offsetAdjustment = CGFLOAT_MAX;
CGFloat horizontalCenter = proposedContentOffset.x +
(CGRectGetWidth(self.collectionView.bounds) / 2.0f);
// 2
CGRect targetRect = CGRectMake(proposedContentOffset.x,
0.0f, self.collectionView.bounds.size.width, self.collectionView.bounds.size.height);
NSArray *array =
[super layoutAttributesForElementsInRect:targetRect];
for (UICollectionViewLayoutAttributes* layoutAttributes in array)
{
// 3
CGFloat distanceFromCenter = layoutAttributes.center.x - horizontalCenter;
if (ABS(distanceFromCenter) < ABS(offsetAdjustment))
{
offsetAdjustment = distanceFromCenter;
}
}
// 4
return CGPointMake(proposedContentOffset.x + offsetAdjustment,
proposedContentOffset.y);

}


any idea?

Answer

I had to scale the cell along the Z axis too:

transform = CATransform3DScale(transform, zoom, zoom, zoom);

the cell touch events works.

does anyone knows why scaling along Z axis is necessary?

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