如何在 UICollectionViewCell 内缩放 UIScrollView?

How to zoom a UIScrollView inside of a UICollectionViewCell?(如何在 UICollectionViewCell 内缩放 UIScrollView?)

问题描述

I'm trying to add a UIScrollView inside of a UICollectionViewCell. The idea is that you can use pinch to zoom the UIScrollView (and with it, the image within), but the scrollview doesn't seem to handle any gesture. I'm guessing they are being caught by the UICollectionView.

I've set the delegate of the UIScrollView to be the UICollectionViewCell, but none of the delegate methods are being called.

EDIT: I've made a github repo with the code (simplified as much as I could). Even though it's just a few lines of code, I cannot see what I did wrong.

EDIT2: After the answer was found, I added the fixes to the above-mentioned repo, hope others find it helpful too :)

https://github.com/krummler/gallery-pinchzoom-example

You might want to try manipulating the UIGestureRecognizers in order to do that. In the GalleryViewController:

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView 
                  cellForItemAtIndexPath:(NSIndexPath *)indexPath {

    GalleryImageCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"galleryImageCell" forIndexPath:indexPath];

    ImageContext *imageContext = [self.images objectAtIndex:indexPath.row];

    cell.imageContext = imageContext;
    [self.collectionView addGestureRecognizer:cell.scrollView.pinchGestureRecognizer];
    [self.collectionView addGestureRecognizer:cell.scrollView.panGestureRecognizer];

    return cell;
}

From Apple's documentation on UIView:

Attaching a gesture recognizer to a view defines the scope of the represented gesture, causing it to receive touches hit-tested to that view and all of its subviews. The view retains the gesture recognizer.

So you'll also want to make sure to remove them when the cell is not showing anymore.

- (void)collectionView:(UICollectionView *)collectionView 
  didEndDisplayingCell:(UICollectionViewCell *)cell 
    forItemAtIndexPath:(NSIndexPath *)indexPath {

    // Get the cell instance and ...
    [self.collectionView removeGestureRecognizer:cell.scrollView.pinchGestureRecognizer];
    [self.collectionView removeGestureRecognizer:cell.scrollView.panGestureRecognizer];
}

Since you're not modifying the UIGestureRecognizer's delegate, only its scope, it will still control the zooming of just that cell's scrollview.

EDIT:

I added the panGestureRecognizer to the above examples, following a suggestion from the OP that it was needed. The zooming itself is completely handled by the pinchGestureRecognizer, but it's true that in most cases, after zooming an image to a point where only a subset of it is visible, you'll want to pan to move the visible portion around. That is, it's part of a proper zooming experience.

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