Question

I am showing a login screen with an error, like:

_loginViewController.error = error;
[_navigationController presentModalController: _loginViewController
                                     animated: YES];

In LoginViewController, I want to slide the error message onto the screen like this:

- (void)showErrorAnimated: (BOOL)animated;
{
    _errorLabel.text = [_error localizedDescription];

    [UIView beginAnimations: @"showError"
                    context: NULL];
    CGRect frame = [_errorView frame];
    frame.origin.y = 0; // starts at -frame.size.height
    [_errorView setFrame: frame];
    [UIView commitAnimations];
}

But I don’t know how to call this to match the timing of the view controller finishing it’s slide to the top of the screen begun by presentModalController:animated:.

How can I get this timing working?

Answer 1

You should use the viewDidAppear method of your controller, which will be called the time the view is displayed.

http://developer.apple.com/library/ios/documentation/uikit/reference/UIViewController_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40006926-CH3-SW17

Just be careful with viewDidAppear because it is called whenever your view is shown. This means that if your controller presents a modal controller and then it is dismissed, the viewWillAppearand viewDidAppear methods will be called again.