Gesture Recognizers: Under the Hood
Now that basic gesture recognizers have been demonstrated in action and the first issue has been encountered with them, it is a good time to walk through, in a little more detail, how gesture recognizers work.
The first thing to understand is that gesture recognizers operate outside the normal view responder chain. The UIWindow will send touch events to gesture recognizers first, and they must indicate that they cannot handle the event in order for touches to get forwarded to the view responder chain by default.
Next, it is important to understand the basic sequence of events that takes place when an app is trying to determine whether a gesture has been recognized:
The window will send touch events to gesture ...
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