Question

Is it possible to pan a UIImageView and when it intersects with the frame of another UIImageView, have that other UIImageView be pushed around by the other UIImageView without just passing over it? I hope that makes sense!

If it is possible, could you give me some ideas on how I’d go about implementing this?

I imagine it would go something like…

If frame intersects frame from left or right on the x/y axis, have the other frame move in that same direction with same distance as the pushing frame. While that logic somewhat makes sense to me, I’m not sure how I’d implement that in code.

I’d really appreciate any advice you can offer.

Answer 1

So, you’re only concerned with left / right panning…

Let’s assume you have 2 UIImageViews, a & b, as subviews of some other UIView and defined as class members of some class.

You can get help detecting panning gestures (dragging touches) on each of these views by creating instances of UIPanGestureRecognizer and adding them to each UIImageView using method addGestureRecognizer:

When creating each UIPanGestureRecognizer, you need to designate a selector to receive the gesture events. Let say it’s called didMove:

Now, some sample code:

- (void) didMove:(UIPanGestureRecognizer*)recognizer {
    UIView* view = [recognizer view];

    // Remember our UIImageViews are class members called, a & b
    //
    UIView* otherView = view == a ? b : a;    

    if (recognizer.state == UIGestureRecognizerStateBegin 
        || recognizer.state == UIGestureRecognizerStateChanged) {

        // Moving left will have a negative x, moving right positive
        //
        CGPoint translation = [recognizer translationInView:view.superview];
        view.center = CGPointMake(view.center.x + translation.x, view.center.y);

        // Reset so we always track the translation from the current view position
        //
        [recognizer setTranslation:CGPointZero inView:view.superview];

        if (CGRectIntersectsRect(view.frame, otherView.frame)) {
            // Translate by the same number of points to keep views in sync
            //
            otherView.center = CGPointMake(otherView.center.x + translation.x, otherView.center.y);
        }
    }
}

It may not be exactly what you need, but it should give you a good idea how it could be done.