ViewController *Controller = [[ViewController alloc] init];  

UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:Controller];  

[self presentViewController:nav animated:YES completion:nil];  

//未登录，跳转到登录页面    TLDLoginViewController *loginVC = [[TLDLoginViewController alloc]init];    TLDNavigationController *nv = [[TLDNavigationController alloc] initWithRootViewController:loginVC];//将普通视图添加到NavigationController    [self presentViewController:nv animated:YES completion:^{        NSLog(@"模态视图");    }];//退出登录页面    [self dismissViewControllerAnimated:YES completion:nil];