在iOS 7，如何检测到系统自带ViewController手势返回结束

-(void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:YES];
    if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0) {
        self.navigationController.delegate = self;
    }
}

- (void)viewWillDisappear:(BOOL)animated
{
    [super viewWillDisappear:YES];
    if ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0) {
        self.navigationController.delegate = nil;
    }
}

- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    id<UIViewControllerTransitionCoordinator> tc = navigationController.topViewController.transitionCoordinator;
    [tc notifyWhenInteractionEndsUsingBlock:^(id<UIViewControllerTransitionCoordinatorContext> context) {
        NSLog(@"7: %i", [context isCancelled]);
    }];
}