UIPanGestureRecognizer and Simultaneous Recognizers
Once a line is selected during a long press, we want the user to be able to move that line around the screen by dragging it with a finger. So we need a gesture recognizer for a finger moving around the screen. This gesture is called panning, and its gesture recognizer subclass is UIPanGestureRecognizer.
Normally, a gesture recognizer does not share the touches it intercepts. Once it has recognized its gesture, it “eats” that touch, and no other recognizer gets a chance to handle it. In our case, this is bad: the entire pan gesture we want to recognize happens within a long press gesture. We need the long press recognizer and the pan recognizer to be able to recognize their gestures simultaneously. ...
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