`1.Specifying a One-Way Relationship Between Two Gesture Recognizer
為了在一個view中（有兩個gesture recognize）制造一個單線程的關系套才，比如你想讓旋轉手勢成功響應并且阻止響應捏合手勢迂猴，可以do like this:
[rotationGestureRecognizer canPreventGestureRecognizer: pinchGestureRecognizer];
(注意看完之后一定要去看 Creating a Custom Gesture Recognizer)
如果不想阻止，就使用如下方法：
gestureRecognizer:shouldRecognizerSimutaneouslyWithGestureRecognizer:
By default, a pinch gesture prevents a rotation and vice versa(反之亦然) because two gestures cannot be recognized at the same time.
對于這之前的內容海需要好好的研讀背伴。
