Question

How to recognize double touch on UIButton ?

Answer 1

Add an target-action for the control event UIControlEventTouchDownRepeat, and do action only when the touch’s tapCount is 2.

Objective-C:

[button addTarget:self action:@selector(multipleTap:withEvent:) 
             forControlEvents:UIControlEventTouchDownRepeat];

...

-(IBAction)multipleTap:(id)sender withEvent:(UIEvent*)event {
   UITouch* touch = [[event allTouches] anyObject];
   if (touch.tapCount == 2) {
     // do action.
   }
}

As @Gavin commented, double-tap on a button is an unusual gesture. On the iPhone OS double-tap is mostly used for zoomable views to zoom into/out of a region of focus. It may be unintuitive for the users if you make the gesture to perform other actions.

Swift 3:

button.addTarget(self, action: #selector(multipleTap(_:event:)), for: UIControlEvents.touchDownRepeat)

And then:

func multipleTap(_ sender: UIButton, event: UIEvent) {
    let touch: UITouch = event.allTouches!.first!
    if (touch.tapCount == 2) {
        // do action.
    }
}