獲取到導航欄裡的所有控制器：
NSMutableArray *viewControllers = [self.navigationController.viewControllers mutableCopy];

for (int i = 0; i < viewControllers.count; i++){
    id vc = viewControllers[i];
    //1.找到要插入介面的前一個介面
    if ([vc isKindOfClass:[LoginViewController class]]){
        UserViewController *insertVC = [[UserViewController alloc] init];
        //2.插入到介面棧中
 

        [viewControllers insertObject:insertVC atIndex:i + 1];
        //3.更新介面棧
        [self.navigationController setViewControllers:viewControllers animated:NO];
        //4.跳轉到指定介面
        [self.navigationController popToViewController:insertVC animated:YES];

        return;
      }
}