ios 侧滑返回

ios7开始 苹果增加了页面 右滑返回的效果；具体的是以UINavigationController为容器的ViewController间右滑切换页面。代码里的设置是：self.navigationController.interactivePopGestureRecognizer.enabled = YES;（default is YES）

可以看到苹果给navigationController添加了一个手势（具体为UIScreenEdgePanGestureRecognizer（边缘手势，同样是ios7以后才有的）），就是利用这个手势实现的 ios7的侧滑返回。问题1：然而事情并非我们想的那么简单。

1.当我们用系统的UINavigationController，并且也是利用系统的navigateBar的时候，是完全没有问题的2.但是当我们没有用系统的navigateBar或者自定义了返回按钮的时候，这个时候 右滑返回是失效的。解决（问题1）办法：对于这种失效的情况，考虑到interactivePopGestureRecognizer也有delegate属性，替换默认的self.navigationController.interactivePopGestureRecognizer.delegate来配置右滑返回的表现也是可行的。我们可以在主NavigationController中设置一下：self.navigationController.interactivePopGestureRecognizer.delegate =(id)self问题2：但是出现很多问题，比如说在rootViewController的时候这个手势也可以响应，导致整个程序页面不响应；push了多层后，快速的触发两次手势，也会错乱解决（问题2）办法：

@interface NavRootViewController : UINavigationController

@property(nonatomic,weak) UIViewController* currentShowVC;

@end

@implementation NavRootViewController-(id)initWithRootViewController:(UIViewController *)rootViewController{

NavRootViewController* nvc = [super initWithRootViewController:rootViewController];

self.interactivePopGestureRecognizer.delegate = self;

nvc.delegate = self;return mvc;

} 

-(void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated{

}

-(void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated{

if (navigationController.viewControllers.count == 1)self.currentShowVC = Nil;elseself.currentShowVC = viewController;

} 

-(BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer{

if (gestureRecognizer == self.interactivePopGestureRecognizer) {return (self.currentShowVC == self.topViewController); //the most important}return YES;

} 

@end

借鉴了别人的方法：具体是通过 获取当前pushView栈里的当前显示的VC,根据这个VC来决定 是否开启手势（如果currentShowVC 是当前显示的，则开启手势；如果 currentShowVC为nil,则代表在主页面，关闭手势）注：当时试了一种方法 就是滑动的时候来回设置 interactivePopGestureRecognizer的delegate；发现 会有crash，原因就是 因为 我把 当前显示的VC设置为了这个手势的delegate，但当这个VC消失的时候，这个delegate便被释放了，导致crash至此，觉得ios7上的右滑返回大功告成了，心里正happy，妈蛋，发现了一个可耻的bug：UIScrollView 上 右滑返回的手势失灵了，靠！！！！！！

问题三：UIScrollView上手势失灵：经研究，发现是UIScrollView上已经添加了 panGestureRecognizer（滑动）手势ios7侧滑返回解决（问题三）办法：参考：http://www.cnblogs.com/lexingyu/p/3702742.html【

解决方案】苹果以UIGestureRecognizerDelegate的形式，支持多个UIGestureRecognizer共存。其中的一个方法是：1 // called when the recognition of one of gestureRecognizer or otherGestureRecognizer would be blocked by the other 2 // return YES to allow both to recognize simultaneously. the default implementation returns NO (by default no two gestures can be recognized simultaneously) 3 // 4 // note: returning YES is guaranteed to allow simultaneous recognition. returning NO is not guaranteed to prevent simultaneous recognition, as the other gesture's delegate may return YES 5 - (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer; 一句话总结就是此方法返回YES时，手势事件会一直往下传递，不论当前层次是否对该事件进行响应。 

@implementation UIScrollView (AllowPanGestureEventPass)- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer{    

if ([gestureRecognizer isKindOfClass:[UIPanGestureRecognizer class]]        && [otherGestureRecognizer isKindOfClass:[UIScreenEdgePanGestureRecognizer class]])    {

        return YES;   

 }    else    { 

       return  NO;   

 }

}

事实上，对UIGestureRecognizer来说，它们对事件的接收顺序和对事件的响应是可以分开设置的，即存在接收链和响应链。接收链如上文所述，和UIView绑定，由UIView的层次决定接收顺序。而响应链在apple君的定义下，逻辑出奇的简单，只有一个方法可以设置多个gestureRecognizer的响应关系：// 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 usage: a single tap may require a double tap to fail - (void)requireGestureRecognizerToFail:(UIGestureRecognizer *)otherGestureRecognizer;每个UIGesturerecognizer都是一个有限状态机，上述方法会在两个gestureRecognizer间建立一个依托于state的依赖关系，当被依赖的gestureRecognizer.state = failed时，另一个gestureRecognizer才能对手势进行响应。所以，只需要[_scrollView.panGestureRecognizer requireGestureRecognizerToFail:screenEdgePanGestureRecognizer];

 - (UIScreenEdgePanGestureRecognizer *)screenEdgePanGestureRecognizer{    UIScreenEdgePanGestureRecognizer *screenEdgePanGestureRecognizer = nil;    if (self.view.gestureRecognizers.count > 0)    { 

       for (UIGestureRecognizer *recognizer in self.view.gestureRecognizers)        { 

           if ([recognizer isKindOfClass:[UIScreenEdgePanGestureRecognizer class]])            { 

               screenEdgePanGestureRecognizer = (UIScreenEdgePanGestureRecognizer *)recognizer;                

break;            }        }    }    

return screenEdgePanGestureRecognizer;

}

参考：牛逼 解决了iOS7下滑动返回与ScrollView共存http://www.cnblogs.com/lexingyu/p/3702742.html更牛逼  解决了interactivePopGestureRecognizer.delegate 的 释放导致crash的问题http://www.2cto.com/kf/201401/272886.html