IOS:以模式方式呈现登录屏幕的代码

Question

我想用登录屏幕(以及首次使用时加入屏幕)来密码保护应用程序。 SO 上的一些答案建议测试用户是否已在初始屏幕的 viewdidappear 中登录，如果未登录，则以模态方式呈现登录屏幕。

我尝试了这个，但代码不起作用。有谁知道用于呈现模态视图 Controller 的最新代码？注意我在 Storyboard中创建了登录屏幕，并为其指定了 Storyboard ID“login”。

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    //if not logged in, modally present login screen here.

    if(![[NSUserDefaults standardUserDefaults] boolForKey:@"loggedIn"]) {
        // go to login screen
        NSLog(@"not logged in");//this fires so logic is ok
        UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
        UIViewController *ivc = [storyboard instantiateViewControllerWithIdentifier:@"login"];//this line gives warning it is not being used
    } else {
        // go to main screen
    }
} 
/*perhaps I should call this somewhere?

- (void)presentModalViewController:(UIViewController *)modalViewController animated:(BOOL)animated
*/

Answer 1

归功于@rdelmar 评论，您必须 presentViewController:animated:completion: (presentModalViewController:animated: ivc。

- (void)viewDidAppear:(BOOL)animated
{
   [super viewDidAppear:animated];
   //if not logged in, modally present login screen here.

   if(![[NSUserDefaults standardUserDefaults] boolForKey:@"loggedIn"]) {
       // go to login screen
       NSLog(@"not logged in");//this fires so logic is ok
       UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
       UIViewController *ivc = [storyboard instantiateViewControllerWithIdentifier:@"login"];//LOOK AT NEXT LINE
       [self presentViewController:ivc animated:YES completion:nil]; //THIS LINE IS MISSING.
  } else {
    // go to main screen
  }
}