Question

I want to define a class of draggable images subclassing UIImageView, separating how they look (on the subclass) and what the user interface react to where they move (on the viewcontroller)

myType1Image.h

@interface myType1Image : UIImageView { } 

myType1Image.m

...
- (void) touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event { 
// Retrieve the initial touch point 
} 
- (void) touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event { 
// Move relative to the original touch point with some special effect
} 
- (void) touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event { 
// Notify the ViewController ... here is my problem...how?
// would call GotIt on viewController for example
}
...

viewcontroller implementation

....
  myType1Image *img = [[myType1Image alloc] initWithImage:[UIImage imageNamed:@"iOSDevTips.png"]];
  img.center = CGPointMake(110, 75);
  img.userInteractionEnabled = YES;
  [subview addSubview:img];
...

- (void) gotIt:(id) (myType1Image *)sender{
    if (CGRectContainsPoint( myimage.frame, [sender.center] )){
        NSLog(@"Got IT!!!");
    }
}

....

I can’t figure out how ViewController could be notified from the myType1Image class, for touchesEnded (for example).
I did it writing all code on the viewcontroller, but I want to do it using subclasses so I can separate the event handling and the visualization of the images from the real funcionality of my interface.
So if I have 15 draggable images, I haven’t to guess what image is touching, and deciding the visual effects to apply.

Is it possible? Is an erroneus aproach?

Answer 1

First, class names should always begin with a capital letter (MyType1Image).

Create a MyType1ImageDelegate protocol in which you declare delegate methods that the image view sends to its delegate (the view controller). The first argument of these methods should always be of the type MyType1Image * (to tell the delegate from which object the message comes).

Your MyType1Image also needs a id <MyType1ImageDelegate> delegate property.

When your view controller creates an image view, it sets itself as the image view’s delegate. Whenever the image view wants to send a message to the view controller, you have it send the message to the delegate.