iOS私有API（二） UIGestureRecognizerDelegate的两个函数

UIGestureRecognizerDelegate有两个没公开的函数，只要重载了就会被调用。

即所有的UIGestureRecognizer子类.delegate = someInstance; 经过set以后，只要这个delegate实例里有这两个函数，就会被调用进入。经过验证，这两个api是可以通过apple审查上app store的。

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer canBePreventedByGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer  
{  
    BOOL result = YES; 
// something you do  
    return result;  
}  
 
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer canPreventGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer   
{  
    BOOL result = YES; 
// something you do  
    return result;  
}

实际上UIGestureRecognizerDelegate这个Protocol有7个函数，公开的只有3个，我目前发现UIWebView系统有使用5个。

@protocol UIGestureRecognizerDelegatePrivate <UIGestureRecognizerDelegate> 
 
@optional 
- (BOOL)_gestureRecognizer:(id)arg1 canBePreventedByGestureRecognizer:(id)arg2; 
- (BOOL)_gestureRecognizer:(id)arg1 canPreventGestureRecognizer:(id)arg2; 
- (BOOL)_gestureRecognizer:(id)arg1 shouldReceiveTouch:(id)arg2; 
- (BOOL)_gestureRecognizer:(id)arg1 shouldRecognizeSimultaneouslyWithGestureRecognizer:(id)arg2; 
- (BOOL)_gestureRecognizerShouldBegin:(id)arg1; 
- (BOOL)_gestureRecognizer:(id)arg1 shouldBeRequiredToFailByGestureRecognizer:(id)arg2; 
- (BOOL)_gestureRecognizer:(id)arg1 shouldRequireFailureOfGestureRecognizer:(id)arg2; 
@end

使用场景：
一个view上以及其superview和subviews上有很多个gestureRecognizers时，可以使用这两个函数做手势间的互斥。如函数名那般顾名思义，返回值为第一个手势能否阻止或被阻止第二个手势的触发。
系统使用示例：
UIWebView的非公开子view，UIWebDocumentView有使用到，经反汇编，其部分实现为：

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer canBePreventedByGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer 
{ 
    BOOL result = NO; 
//    有部分代码省略
    if (_longPressGestureRecognizer != gestureRecognizer && _highlightLongPressGestureRecognizer != gestureRecognizer) 
        result = YES; 
    return result; 
} 
 
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer canPreventGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer 
{ 
    BOOL result = YES; 
//    有部分代码省略
    if (_highlightLongPressGestureRecognizer == gestureRecognizer || _longPressGestureRecognizer == gestureRecognizer) 
    { 
        Class cls = NSClassFromString(@"UIScrollViewPanGestureRecognizer"); 
        result = [otherGestureRecognizer isKindOfClass:cls] == NO; 
    } 
    return result; 
}