Question

I am struggling with understanding why the first method below works for hiding and removing a subview of a view. In this first method I pass the pointer by reference. In the second method, which is less general, I have a delegate method designed for removing a specific view. I would like to use the first method, because I have several views that I would like to apply this too. I should mention that the first method works without fail as long as it is called within the implementing class. It fails when I call it from the view controller that I wish to dismiss. I get an EXC_BAD_ACCESS on the removeFromSuperview line when it fails in the first method.

-(void)closeView:(UIViewController **)viewController
{
 [UIView transitionWithView:self.view 
                   duration:UINavigationControllerHideShowBarDuration
                    options:UIViewAnimationOptionCurveLinear
                 animations:^
  {
   [[*viewController view] setAlpha:0.0];
  }
                 completion:^(BOOL finished)
  {   
   [[*viewController view] removeFromSuperview];
   [*viewController release], *viewController = nil;
  }];
}

-(void)closeButtonClicked
{
 [delegate closeView:&self];
}

//
// This method works without fail:
//

-(void)closeView
{
 [UIView transitionWithView:self.view 
                   duration:UINavigationControllerHideShowBarDuration
                    options:UIViewAnimationOptionCurveLinear
                 animations:^
  {
   // In this context viewController is defined in the class interface
   [[viewController view] setAlpha:0.0];
  }
                 completion:^(BOOL finished)
  {      
   [[viewController view] removeFromSuperview];
   [viewController release], viewController = nil;       
  }];
}

-(void)closeButtonClicked
{
 [delegate closeView];
}

Answer 1

First of all, it is not according to the style guides, and not a good idea in general, to do a release of the viewController within a method like this. It will get you into trouble quickly. If the caller of this method is responsible for the viewController (it has done the retain), then it should release it as well. This is likely the cause of the first method not working from within the viewcontroller itself.

In the second method you do not pass in the viewController as parameter, which means it needs to be defined in the context.

If you don’t release the viewController in this method, then you don’t need to set its variable to nil either, and you can simply pass it as normal parameter:

-(void)closeView:(UIViewController *)viewController
{
 [UIView transitionWithView:self.view 
                   duration:UINavigationControllerHideShowBarDuration
                    options:UIViewAnimationOptionTransitionCrossDissolve
                 animations:^
  {
    [[viewController view] removeFromSuperview];
  }
                 completion:nil];
}

you would then do this at the call-site:

[self closeView:childViewController];
[childViewController release]; childViewController = nil;

It safe to release the child in this way before the animation is done, because the animations block implicitly retains all objects referenced from the block, including the viewController parameter. Therefore, the child’s dealloc is not called until the animations block releases it.
This does not work in your first code example, because you pass a pointer to a variable. That is, the animations block does not know it needs to retain the child.

BTW, I am not sure why you want to set the alpha, in the example above I show that you can also remove the view already in the animations block. See more about that in the UIView Class Reference.