How to recognize swipe gesture in UIScrollView

Solution 1:

Figured it out. In my case, my UIScrollView contained a UIImage that I allowed zooming. Apparently that meant that scrolling is enabled and the UIScrollView had trouble distinguishing between gestures intended to scroll vs. swipe (next, previous image).

The key in my case, is to disable scrolling in the scroll view when the image is not zoomed in, and renabled it when it is zoomed in. This provides the expected behavior.

The critical piece is to put the following in the scroll view's delegate:

- (void)scrollViewDidZoom:(UIScrollView *)scrollView {
  if (scrollView.zoomScale!=1.0) {
    // Zooming, enable scrolling
    scrollView.scrollEnabled = TRUE;
  } else {
    // Not zoomed, disable scrolling so gestures get used instead
    scrollView.scrollEnabled = FALSE;
  }
}

I also have to initialize the scroll view with scrolling disabled. To enable zooming, simply provide an image on a delegate call,

- (UIView *)viewForZoomingInScrollView:(UIScrollView *)scrollView {
  // Return the scroll view
  return myImage;
}

And set a few parms in viewDidLoad for the zooming and setup gesture recognizers as well

- (void)viewDidLoad {
  [super viewDidLoad];
  myScrollView.contentSize = CGSizeMake(myImage.frame.size.width, myImage.frame.size.height);
  myScrollView.maximumZoomScale = 4.0;
  myScrollView.minimumZoomScale = 1.0;
  myScrollView.clipsToBounds = YES;
  myScrollView.delegate = self;

  [myScrollView addSubview:myImage];
  [self setWantsFullScreenLayout:TRUE];

  myScrollView.scrollEnabled = FALSE; 
  UISwipeGestureRecognizer *recognizer = 
    [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipeFrom:)];
  recognizer.delaysTouchesBegan = TRUE;
  [myScrollView addGestureRecognizer:recognizer];
  [recognizer release];

  recognizer = [[UISwipeGestureRecognizer alloc] initWithTarget:self action:@selector(handleSwipeFrom:)];
  recognizer.direction = UISwipeGestureRecognizerDirectionLeft;
  [myScrollView addGestureRecognizer:recognizer];
  [recognizer release];
  [myScrollView delaysContentTouches];
}

Solution 2:

UIScrollView *scrollView = ...
UISwipeGestureRecognizer *mySwipe = ...

The correct solution to fix this issue is to add one line of code:

[scrollView.panGestureRecognizer requireGestureRecognizerToFail:mySwipe]

Swift version:

scrollView.panGestureRecognizer.requireGestureRecognizerToFail(mySwipe)

Swift4 version:

scrollView.panGestureRecognizer.require(toFail: mySwipe!);