//dismiss到根视图

 - (void)dismissToRootViewController{

     UIViewController *vc = self;

     while (vc.presentingViewController) {

         vc = vc.presentingViewController;

     }

     [vc dismissViewControllerAnimated:YES completion:nil];

 }
//这种更有效

　　UIViewController *vc =self.presentingViewController;

while (![vc isKindOfClass:[[UIApplication sharedApplication].keyWindow.rootViewController class]]) {

vc = vc.presentingViewController;

}

[vc dismissViewControllerAnimated:YES completion:nil];

     //dismiss到指定界面

     UIViewController *vc =self.presentingViewController;

     while (![vc isKindOfClass:[[UIApplication sharedApplication].keyWindow.rootViewController class]]) {

         vc = vc.presentingViewController;

     }

     [vc dismissViewControllerAnimated:YES completion:nil];

  [self.navigationController popToRootViewControllerAnimated:YES];//pop到根视图

   for (UIViewController *controller in self.navigationController.viewControllers) {

         if ([controller isKindOfClass:[WekeWordLockViewController class]]) {

             WekeWordLockViewController *vc = (WekeWordLockViewController *)controller;

             [self.navigationController popToViewController:vc animated:YES];

         }

     }