UIGestureRecognizer is an abstract base class for concrete gesture-recognizer classes. A gesture-recognizer object (or, simply, a gesture recognizer) decouples the logic for recognizing a gesture and acting on that recognition. When one of these objects recognizes a common gesture or, in some cases, a change in the gesture, it sends an action message to each designated target object.
The
UIGestureRecognizerclass defines a set of common behaviors that can be configured for all concrete gesture recognizers. It can also communicate with its delegate (an object that adopts theUIGestureRecognizerDelegateprotocol), thereby enabling finer-grained customization of some behaviors.A gesture recognizer operates on touches hit-tested to a specific view and all of that view’s subviews. It thus must be associated with that view. To make that association you must call the
UIViewmethodaddGestureRecognizer:. A gesture recognizer does not participate in the view’s responder chain.A gesture recognizer has one or more target-action pairs associated with it. If there are multiple target-action pairs, they are discrete, and not cumulative. Recognition of a gesture results in the dispatch of an action message to a target for each of those pairs. The action methods invoked must conform to one of the following signatures:
- (void)handleGesture;
- (void)handleGesture:(UIGestureRecognizer *)gestureRecognizer;
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