由于以前没有很细致的研究过长按手势，所以今天使用的时候发现长按手势会调用两次响应事件。
主要原因是长按手势会分别在UIGestureRecognizerStateBegan和UIGestureRecognizerStateEnded状态时调用响应函数
这时就需要在响应事件中增加手势状态的判断，根据具体的应用情况在相应的状态中执行操作。
typedefNS_ENUM(NSInteger, UIGestureRecognizerState) {
UIGestureRecognizerStatePossible,// the recognizer has not yet recognized its gesture, but may be evaluating touch events. this is the default state
UIGestureRecognizerStateBegan,// the recognizer has received touches recognized as the gesture. the action method will be called at the next turn of the run loop
UIGestureRecognizerStateChanged,// the recognizer has received touches recognized as a change to the gesture. the action method will be called at the next turn of the run loop
UIGestureRecognizerStateEnded,// the recognizer has received touches recognized as the end of the gesture. the action method will be called at the next turn of the run loop and the recognizer will be reset to UIGestureRecognizerStatePossible
UIGestureRecognizerStateCancelled,// the recognizer has received touches resulting in the cancellation of the gesture. the action method will be called at the next turn of the run loop. the recognizer will be reset to UIGestureRecognizerStatePossible
UIGestureRecognizerStateFailed,// the recognizer has received a touch sequence that can not be recognized as the gesture. the action method will not be called and the recognizer will be reset to UIGestureRecognizerStatePossible
// Discrete Gestures – gesture recognizers that recognize a discrete event but do not report changes (for example, a tap) do not transition through the Began and Changed states and can not fail or be cancelled
UIGestureRecognizerStateRecognized =UIGestureRecognizerStateEnded// the recognizer has received touches recognized as the gesture. the action method will be called at the next turn of the run loop and the recognizer will be reset to UIGestureRecognizerStatePossible
};
if (longPressGesture.state == UIGestureRecognizerStateBegan) {
// do something
}else if (longPressGesture.state == UIGestureRecognizerStateEnded){
// do something
}
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