- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    
    self.window = [[UIWindow alloc]initWithFrame:[[UIScreen mainScreen] bounds]];
    
    ViewController* viewController = [[ViewController alloc]
                                          initWithNibName:@"ViewController" bundle:nil];
    
    self.navigationController = [[UINavigationController alloc]
                                 initWithRootViewController:viewController];
    
    self.window.rootViewController = self.navigationController;
    [self.window makeKeyAndVisible];
    
    return YES;
}

SecondViewController* secondView = [[SecondViewController alloc]
                                      initWithNibName:@"SecondViewController" bundle:nil];
    
    [self.navigationController pushViewController:secondView animated:nil];

    //回到上一级视图
//    [self.navigationController popViewControllerAnimated:YES];
    
    //回到根视图
//    [self.navigationController popToRootViewControllerAnimated:YES];
    
    //回到指定视图
    NSArray * ctrlArray = self.navigationController.viewControllers;
    [self.navigationController popToViewController:[ctrlArray objectAtIndex:0] animated:YES];