Unpinch custom gesture recognizer with three fingers in iOS

Question

I want to make a custom gesture recognizer with three fingers. Which is similar to unpinch gesture recognizer.

All I need is an idea about how to recognize it.

My gesture needs to recognize three fingers with three directions. For example:

I hope images makes sense. I need to make it flexible for any three opposite directions. Thanks in advance. Any help would be appreciated.

I am aware about the subclass methods and I've created custom gestures already with single finger like semicircle, full circle. I need a coding idea about how to handle that.

Answer 1

You need to create a UIGestureRecognizer subclass of your own (let's call it DRThreeFingerPinchGestureRecognizer) and in it to implement:

– touchesBegan:withEvent:
– touchesMoved:withEvent:
– touchesEnded:withEvent:
– touchesCancelled:withEvent:

These methods are called when touches are accepted by the system and possibly before they are sent to the view itself (depending on how you setup the gesture recognizer). Each of these methods will give you a set of touches, for which you can check the current location in your view and previous location. Since pinch gesture is relatively very simple, this information is enough for you to test if the user is performing a pinch, and fail the test (UIGestureRecognizerStateFailed). If state was not failed by – touchesEnded:withEvent:, you can recognize the gesture.

I say pinch gestures are simple, because you can easily track each touch and see how it moves compared to other touches and itself. If a threshold of an angle is passed and broken, you fail the test, otherwise you allow it to continue. If touches do not move in separate angles to each other, you fail the test. You will have to play with what angles of the vectors are acceptable, because 120 degrees are not optimal for the three most common fingers (thumb + index + middle fingers). You may just want to check that the vectors are not colliding.

Make sure to read the UIGestureRecognizer documentation for an in-depth look at the various methods, as well as subclassing notes.