如何将轻击手势添加到从dequeueReusableCellWithReuseIdentifier返回的UICollectionViewCell子视图中

Question

What's the best method for efficiently adding a tap gesture to a subview of a UICollectionViewCell returned from dequeueReusableCellWithReuseIdentifier that already has a bunch of default gesture recognizers attached to it (such as a UIScrollView ). Do I need to check and see if my one custom gesture is already attached ( scrollView.gestureRecognizers ) and if not then add it? I need my app's scrolling to be as smooth as possible so performance of the check and efficient reuse of already created resources is key. This code all takes place inside cellForItemAtIndexPath . Thanks.

Answer 1

I figured out a way to do it that requires only a single, shared, tap gesture recognizer object and moves the setup code from cellForItemAtIndexPath (which gets called very frequently as a user scrolls) to viewDidLoad (which gets called once when the view is loaded). Here's the code:

- (void)myCollectionViewWasTapped:(UITapGestureRecognizer *)tap
{
    CGPoint tapLocation = [tap locationInView:self.collectionView];
    NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint:tapLocation];
    if (indexPath)
    {
        MyCollectionViewCell *cell = (MyCollectionViewCell *)[self.collectionView cellForItemAtIndexPath:indexPath];
        CGRect mySubviewRectInCollectionViewCoorSys = [self.collectionView convertRect:cell.mySubview.frame fromView:cell];
        if (CGRectContainsPoint(mySubviewRectInCollectionViewCoorSys, tapLocation))
        {
            // Yay! My subview was tapped!
        }
    }
}

- (void)viewDidLoad
{
    // Invoke super
    [super viewDidLoad];

    // Add tap handler to collection view
    UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(myCollectionViewWasTapped:)];
    [self.collectionView addGestureRecognizer:tap];
}

Answer 2

Here's a rough, very simple outline of a possible design solution: you could subclass UICollectionViewCell and override its initialization methods to add the gesture recognizer to its subviews. Furthermore, if you don't want the cell to "know" about the gesture recognizer, you could create a protocol that the data source object would conform to. The cell object would call a "setup" protocol method at the appropriate time.

Hope this helps!