On zoom, UIScrollview subviews not recognizing gesture

Question

I have a scrollview to which I have added an image view as a subview. The contentsize of the scrollview is same as the size of the imageview (width and height). There are two buttons outside the scrollview. When I click on either on them, a small rectangle view is added as a subview to the imageview. This rectangle view can be dragged anywhere on the imageview by the user after it has been added.

This works fine until I pinch to zoom the scrollview. In the viewForZoomingInScrollView: method, I return the imageview and the zooming works fine. But in the zoomed view when I try to drag around the rectangle view, it does not move. It does not recognize the pan gestures any more. Any idea why this is happening?

Thanks

Hetal

Is nothing happening when you try to drag the rectangle view or is the scrollView paned instead? — Tobi
The scrollview is panned instead when I try dragging on the rectangle. But there is also some little portion on the rectangle where if I drag, it does drag the rectangle. — Hetal Vora
Could you provide your code for setting up the scroll view, rectangle view, gesture recognizer and the pan handling method. I ran a quick test and everything works fine... — Tobi
Oh wait I just realized you mentioned adding the rectangle view as subview of the UIImageView? I don't think image views are supposed to have subviews. What happens if you just add the rectangle as subview of the scrollview? — Tobi
In that case, the rectangle does not zoom when I pinch to zoom. Only the imageview gets zoomed. Hence I had to add the rectangle to the image view. — Hetal Vora

Tobi Tobi · Accepted Answer · 2012-10-25T19:11:29

Following up to your last comment, I'd suggest to try the following:

In your viewDidLoad method add this:

for (UIGestureRecognizer *gr in self.scrollView.gestureRecognizers) {
    if ([gr isKindOfClass:[UIPanGestureRecognizer class]])
    {
        [gr requireGestureRecognizerToFail:self.dragGR];
    }
}

where dragView is your rectangleView.

The following is probably not necessary for the above to work, but it might be good practice to clean up the view hierarchy anyway:

Add a plain UIView as superview of your image view with the same frame and add the rectangle view as subview of that new view. In your viewForZoomingInScrollView: return that new view. As I said in the comments I don't think adding subviews to UIImageViews is considered good practice. But maybe that's just my opinion :)

On zoom, UIScrollview subviews not recognizing gesture

2 Answers