UIAlertView Delegates

Question

Can someone explain how the delegate to a UIAlertView works? Is it automatically called or do I have to call it? Eg:

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex

Answer 1

So long as you're correctly setting the delegate property of the UIAlertView and implementing the protocol, it will be automatically called when a user clicks on a button in your alert.

Take a look at the projects listed under "Related sample code" at http://developer.apple.com/library/ios/#documentation/UIKit/Reference/UIAlertViewDelegate_Protocol/UIAlertViewDelegate/UIAlertViewDelegate.html to see it in action.

Answer 2

The alertView:clickedButtonAtIndex: method of the delegate is automatically called by UIAlertView. The init method for UIAlertView takes a delegate as one of the parameters. Just make sure to pass in an object that responds to alertView:clickedButtonAtIndex:.

Answer 3

Let's say you showed an alert where the delegate was "self"

- (void)showAlert {
        UIAlertView *myAlert = [[UIAlertView alloc] initWithTitle:@"My Alert" 
                                                       message:@"Do you want to continue?"
                     delegate:self
                  cancelButtonTitle:nil
                  otherButtonTitles:@"No", @"Yes", nil];
        [myAlert show];
        [myAlert release];
}

In order for the following to work in your .m file:

- (void)alertView:(UIAlertView *)alertView clickedButtonAtIndex:(NSInteger)buttonIndex

Your .h file will need to reference the UIAlertViewDelegate in the implementation statement like so:

@interface myViewController : UIViewController <UIAlertViewDelegate> {
}

This is what allows your .m file to respond to UIAlertViewDelegate method calls.