试图在过渡过程中开始模式转换

Question

我正在检查用户是否登录到Facebook。如果是的话，我想把它们转移到另一个视图。

我遇到的问题是，在视图实际加载之前，loginViewFetchedUserInfo和loginViewShowingLoggedInUser都会被调用。

正因为如此，当调用[self showWelcome:self]时，我得到一个“试图在转换过程中开始模态转换”错误()。

在将视图发送到新视图之前，我似乎想不出一种等待视图完成加载的方法。

- (void)loginViewShowingLoggedInUser:(FBLoginView *)loginView {

    // Set flag
    isFirstLoginDone = YES;

    NSLog(@"User is logged in");
}

- (void)loginViewFetchedUserInfo:(FBLoginView *)loginView
                        user:(id<FBGraphUser>)user {

    // Check first login
    if(isFirstLoginDone) {
         [self showWelcome:self];
    }

    // clear the flag
    isFirstLoginDone = NO;

}

- (IBAction)showWelcome:(id)sender
{
    UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"WelcomeStoryboard" bundle:nil];
    UIViewController *vc = [mainStoryboard instantiateViewControllerWithIdentifier:@"WelcomeController"];
    [self presentViewController:vc animated:YES completion:nil];
}

Answer 1

是的，当您在出现一个viewController时，出现了另一个viewController。为此，按照下面的代码创建一个虚拟方法，并以较小的时间间隔启动它。

- (IBAction)showWelcome:(id)sender{
   [self someMethod];
}

-(void)someMethod{
    if(self.isBeingPresented){
        [self performSelector:@selector(someMethod) withObject:nil afterDelay:.1];
    }
    else{
        UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:@"WelcomeStoryboard" bundle:nil];
        UIViewController *vc = [mainStoryboard instantiateViewControllerWithIdentifier:@"WelcomeController"];
        [self presentViewController:vc animated:YES completion:nil];
    }
}