Event listener for the position of a UIImageView

How would I be able to call a method, according to the y coordinate of a UIImage view? To be more specific, I have a dragable UIImageView. When the y co-ordinate of it is greater than a certain开发者_如何转开发 value, I want the colour of the screen to change.

code for dragging:

- (void) touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{

UITouch *touch = [[event allTouches] anyObject];

 if([touch view] == toggle)

 {



    CGPoint location = [touch locationInView:self.view];
    CGPoint newLocation = CGPointMake(toggle.center.x, location.y);

    toggle.center = newLocation;
    NSLog(@"%f \n",toggle.center.y);

}  

}

I could think of two ways of doing this. First is Key-Value Observing via the following:

[self.toggle addObserver: inspector
              forKeyPath: @"frame"
                 options: NSKeyValueObservingOptionNew
                 context: NULL];

I'm not sure if the frame property is Key-Value Coding compliant, though.

Or, and this is what I would recommend, you can:

(1) Create a [Prefix]ToggleViewLocationDelegate protocol, and add a locationDelegate property to your view/view controller, like so:

// YourViewOrViewControllerClass.h
// ...


@class YourViewOrViewControllerClass

@protocol [Prefix]ToggleViewLocationDelegate

- (void) toggleViewDidChangeFrame: (UIView*) toggleView;

@end

@class YourViewOrViewControllerClass

@property (nonatomic, assign) id<[Prefix]ToggleViewLocationDelegate> locationDelegate;
...

@end

(2) Make the class interested in the coordinate changes conform to the protocol, and (3) In the touchesMoved:withEvent: method, inform the locationDelegate, like so:

- (void) touchesMoved: (NSSet*)   touches
            withEvent: (UIEvent*) event
{
  UITouch* touch = [touches anyObject];
  if (touch.view == toggle)
  {
    /* Fetch the new touch location */
    CGPoint location = [touch locationInView: self.view];

    /* Set the toggle's location */
    CGPoint newLocation = CGPointMake(toggle.center.x, location.y);
    toggle.center = newLocation;

    /* Inform the delegate when applicable */
    if (self.locationDelegate != nil)
    {
      [self.locationDelegate toggleViewDidChangeFrame: toggle];
    }
  }
}