Question

I have a question that I’ve searched but can’t find a definative answer to. Here is my layout:

UIView - ViewController   
   |_UIScrollView - added programatically
      | |_UIView to hold a backgound/perimeter  - added programmatically
      |_UIView 1 - added programmatically
      |_UIView 2 - added programmatically
       and so on

My question is how come the ViewController calls “touchesMoved” only once when I move say UIView 2 on touch?

Now UIView has it’s own touchesMoved method, but I need the controller’s touchesMoved to get called as I need it to talk to the ScrollView to update its position. Such as when that UIView 2 is near the corner, so that the ScrollView moves a little to fully show UIView 2.

If there is no way around this is there a way to update ScrollView from UIView 2 to scroll when its near a corner?

Edit:

I think I may have found a work around. Not sure if this will be accepted by Apple but:

I just made a call to a instance variable that is = to self.superview which then allows me to talk back to my ScrollView within UIView’s touchesMoved

in that i can call the method [ScrollView setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated] so my ScrollView gets updated as the subview(UIView2) moves close to the edge of the UIWindow.

Thank you for the suggestions.

Answer 1

The behavior you describe is the result of the UIScrollView hijacking the touch moved event. In other words, as soon as the UIScrollView detect that a touch moved event falls within its frame, it takes control of it. I experienced the same behavior while trying so create a special swipe handler, and it failed each time a UIScrollView was also interested by the swipe.

In my case, I solved the issue by intercepting the event in sendEvent: overridden in my custom UIWindow, but I don’t know if you want to do the same. In any case, this is what worked for me:

- (void)sendEvent:(UIEvent*)event {
NSSet* allTouches = [event allTouches];
UITouch* touch = [allTouches anyObject];
UIView* touchView = [touch view];

//-- UIScrollViews will make touchView be nil after a few UITouchPhaseMoved events;
//-- by storing the initialView getting the touch, we can overcome this problem
if (!touchView && _initialView && touch.phase != UITouchPhaseBegan)
    touchView = _initialView;

    //-- do your own management of the event

    //-- let the event propagate if you want also the default event management
[super sendEvent:event];

}

An alternative approach that you might investigate is attaching a gesture recognizer to your views — they have a pretty high priority, so maybe the UIScrollView will not mess with them and it might work better for you.

If there is no way around this is there a way to update ScrollView from UIView 2 to scroll when its near a corner?

Have you tried to make the UIScrollView scroll by calling:

- (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated