objective-c - 错误:在应用程序启动结束时，应用程序应具有 Root View Controller

Question

打开应用程序时，我首先调用UIAlertView，但出现错误Applications are expected to have a root view controller at the end of application launch
任何想法为什么会这样

- (void)viewDidLoad
{
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
if([userDefaults stringForKey:@"kUserName"] == nil) 
{
    NSLog(@"enter a username");
    askForUserName = [[UIAlertView alloc] initWithTitle:@"First time here I see!" 
                                                             message:@"Please enter a username:\n\n" 
                                                            delegate:self 
                                                            cancelButtonTitle:@"Done" 
                                                            otherButtonTitles:nil];


    CGRect frame = CGRectMake(48, 70, 200, 20);
    usernameField = [[UITextField alloc] initWithFrame:frame];
    usernameField.placeholder = @"Username";        
    usernameField.backgroundColor = [UIColor whiteColor];       
    usernameField.autocorrectionType = UITextAutocorrectionTypeDefault;         
    usernameField.keyboardType = UIKeyboardTypeAlphabet;        
    usernameField.returnKeyType = UIReturnKeyDefault;   
    usernameField.clearButtonMode = UITextFieldViewModeWhileEditing;
    [askForUserName addSubview:usernameField];  

    [askForUserName show];        


} else
{
    userName = [userDefaults stringForKey:@"kUserName"];
}

// Do any additional setup after loading the view, typically from a nib.
}

Answer 1

我也注意到这是在我的一个应用程序中发生的。我认为这是因为UIAlertViews阻止了触发应用程序的主线程。我从来没有任何实际的问题(它不会使应用程序或任何应用程序崩溃)，但是您可以尝试在延迟后使用NSTimer和阻塞/不同线程来调用它，以消除警告。