- (void)viewDidLoad
{
    [super viewDidLoad];
 // Do any additional setup after loading the view.
    
    // draw a shadow for navigation view to differ the layers obviously.
    // using this way to draw shadow will lead to the low performace
    // the best alternative way is making a shadow image.
    //

//    self.recognizer = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(paningGestureReceive:)];
//    self.recognizer.delegate = self;
//    [self.recognizer delaysTouchesBegan];
//    [self.view addGestureRecognizer:self.recognizer];

//[MyUserService shareService].isCanDragBack:这个用来判断是否开启拖拽手势    

    //系统的返回手势
    if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0) {
        // 获取系统自带滑动手势的target对象
        id target = self.interactivePopGestureRecognizer.delegate;
        // 创建全屏滑动手势，调用系统自带滑动手势的target的action方法
        UIScreenEdgePanGestureRecognizer *pan = [[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:target action:@selector(handleNavigationTransition:)];
        pan.edges = UIRectEdgeLeft;//左侧
        // 设置手势代理，拦截手势触发
        pan.delegate = self;
        // 给导航控制器的view添加全屏滑动手势
        [self.view addGestureRecognizer:pan];
        // 禁止使用系统自带的滑动手势
        self.interactivePopGestureRecognizer.enabled = NO;   // 手势的代理设置为self
    }
}

- (void)handleNavigationTransition:(UIGestureRecognizer *)recoginzer{
    
}

// 什么时候调用：每次触发手势之前都会询问下代理，是否触发。
// 作用：拦截手势触发

- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
{
    // 注意：只有非根控制器才有滑动返回功能，根控制器没有。
    // 判断导航控制器是否只有一个子控制器，如果只有一个子控制器，肯定是根控制器
    if (self.childViewControllers.count == 1) {
        // 表示用户在根控制器界面，就不需要触发滑动手势，
        return NO;
    }
    return YES;
}

- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldReceiveTouch:(UITouch *)touch {
    
    if (self.viewControllers.count <= 1 || ![MyUserService shareService].isCanDragBack)
        return NO;
    
    return YES;
}