官方文档这样写道 create a relationship with another gesture recognizer that will prevent this gesture’s actions from being called until otherGestureRecognizer transitions to UIGestureRecognizerStateFailed if otherGestureRecognizer transitions to UIGestureRecognizerStateRecognized or UIGestureRecognizerStateBegan then this recognizer will instead transition to UIGestureRecognizerStateFailed example::a single tap may require a double tap to f
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