Drag event in subview of UIScrollView

Question

How can I add a drag event to a subview of a UIScrollView? The structure is the following:

-UIView
   -UIScrollView
      -UIView
      -UIView
        ...

I tried to start with the following:

-(void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *aTouch = [touches anyObject];
CGPoint location = [aTouch locationInView:self.superview.superview];
[UIView beginAnimations:@"Dragging A DraggableView" context:nil];
self.frame = CGRectMake(location.x, location.y, 
                        self.frame.size.width, self.frame.size.height);
[UIView commitAnimations];

}

But nothing happens! Help would be very much appreciated. Thanks

Answer 1

Just incase anyone finds this question like I did, I solved this problem by adding a gesture recognizer to the subviews in the scrollview. The gesture recognizer will handle the touch event itself.

Answer 2

Bruno, one possibility is to use the gesture recognizers, as Scott mentions.

Another possibility is to use the touchesMoved: method you mention. Using the touchesMoved: method requires you to implement another three methods, touchesBegan:, touchesEnded:, touchesCancelled:. They cover the phases of the finger touching the screen:

• First contact (touchesBegan) allows you to set up variables as needed.
• Continuous move (touchesMoved) allows you to track the move and move your content continuously.
• And finally removing the finger (touchesEnded) where you can finalize any changes you want to keep.
• touchesCancelled is required for clean-up if the gesture is interrupted (by phone call, or some other controller grabbing the touch event).

You need all four methods on the same class, otherwise a superclass implementing the method will grab the touch processing and your code won't run as expected.

Regards, nobi