iOS UINavigationController後退按鈕事件

-(void) viewWillDisappear:(BOOL)animated
{
if ([self.navigationController.viewControllers indexOfObject:self]==NSNotFound)
{
// back button was pressed. We know this is true because self is no longer
// in the navigation stack.
NSLog(@”back button was pressed.”);
}
[super viewWillDisappear:animated];
}