Question

I have seen the sample application of iPhone MP-movie player – controller.

They have added a notification on the sample code.

// Register to receive a notification that the movie is now in memory and ready to play
[[NSNotificationCenter defaultCenter] addObserver:self 
                 selector:@selector(moviePreloadDidFinish:) 
                 name:MPMoviePlayerContentPreloadDidFinishNotification 
                 object:nil];

In above code, When MPMoviePlayerController finishes loading, it invokes moviePreloadDidFinish method.

Similarly, I want to fire an method when user press back button from navigation bar, (back to previous view controller through navigation controller ).

I don’t know how to add a notification for that.

Answer 1

Put your own custom back button in the navigationItem:

UIBarButtonItem *btn = [[UIBarButtonItem alloc] initWithImage:yourImage style:UIBarButtonItemStyleBordered target:self action:@selector(goBack)];
self.navigationItem.leftBarButtonItem = btn;
[btn release];

In the goBack method of your viewController, you’ll put whatever code you need and then pop the viewController:

- (void)goBack {
 /* your code here */

[self.view.navigationController popToRootViewControllerAnimated:YES];
}