Question

Is it possible to fire a UIPinchGestureRecognizer action just once?

I want to enable my users to pinch (actually spread) to fire of an action but the method gets called constantly which I understand is the functionality of a UIPinchGestureRecognizer.

UPDATED CODE USING ANSWER BELOW (just detects zoom):

-(void) handlePinchGesture: (UIPinchGestureRecognizer *) sender {
    if (sender.state == UIGestureRecognizerStateBegan) {
        self.startingScale = sender.scale;
    }
    if (sender.state == UIGestureRecognizerStateEnded) {
        if (sender.scale > self.startingScale) {
            [self zoomIn];
        }
    }
}

Answer 1

Gesture recognizers are state machines, and if you don’t specify which state you want to listen to simply calling a selector from a gesture will fire for any/every state across the board.

To limit detection to when the gesture starts you can use:

- (void)myGestureRecognized:(UIGestureRecognizer*)sender
{
    if (sender.state == UIGestureRecognizerStateBegan) {
        //do something
    }
}

Other recognition states include:

typedef enum {
   UIGestureRecognizerStatePossible,

   UIGestureRecognizerStateBegan,
   UIGestureRecognizerStateChanged,
   UIGestureRecognizerStateEnded,
   UIGestureRecognizerStateCancelled,

   UIGestureRecognizerStateFailed,

   UIGestureRecognizerStateRecognized = UIGestureRecognizerStateEnded
} UIGestureRecognizerState;