Supposing you have a UITapGestureRecognizer attached to a UIImageView, and you’d like your users to know that the image is tappable, a good way to do so is subtly highlight the image when it is touched.

UIImageViews have a setHighlightedImage method that can be used, but only if your image is static, and therefore you can create the ‘highlighted’ image in advance.

Instead, to achieve the effect we’d like, we need to subclass UIImageView. Override the following methods in the subclass:

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

self.alpha = 0.8;

}

 

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

//The touch may be cancelled, due to scrolling etc. Restore the alpha if that is the case.

self.alpha = 1;

 

}

 

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

//Restore the alpha to its original state.

self.alpha = 1;

}

 

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

 

}

 

Touching the UIImageView will now make it somewhat transparent. (The touchesMoved method is left blank, as suggested by the Apple docs – when overriding any of the above methods without calling super,  the other methods must be implemented, even if they are only stubs. Also note that userInteractionEnabled needs to be set to yes after initializing the imageView.)

To create a highlighted overlay effect, simply change the background color of the UIImageView to, say, black, in its init method.

Now simply change your existing UIImageViews to instances of your custom subclass (works inside TableView Cells also) , to enable the highlighting effect.