Question

I am getting this cryptic message: wait_fences: failed to receive reply: 10004003
I have googled and people think it has something to do with not properly dismissing a UITextField or Alert. I have one textfield in my app and I assure you I release it properly using resignFirstResponder, etc…
I get this message when I am opening a MPMusicPickerController from a subview, does that make any difference. I really need to get this fixed because it is messing up my whole app!

Thanks,
Brad

Edit1:

    - (IBAction)openMediaPicker:(id)sender {
    [[UIApplication sharedApplication] setStatusBarHidden:YES withAnimation:UIStatusBarAnimationFade];
    MPMediaPickerController *mediaPicker = [[MPMediaPickerController alloc] initWithMediaTypes:MPMediaTypeAny];
    mediaPicker.delegate = self;
    mediaPicker.allowsPickingMultipleItems = YES;
    mediaPicker.prompt = @"Select songs to play";
    [self presentModalViewController:mediaPicker animated:YES];
    [mediaPicker release];
} 

// Media picker delegate methods
- (void)mediaPicker: (MPMediaPickerController *)mediaPicker didPickMediaItems:(MPMediaItemCollection *)mediaItemCollection {

    AppAppDelegate *appDelegate = (AppAppDelegate *)[[UIApplication sharedApplication] delegate];
    [appDelegate.tr2 stop];
    [playstopButton setHidden:NO];
    [playstopButton setImage:[UIImage imageNamed:@"Stop-Music-Button.png"] forState:UIControlStateNormal];
    // We need to dismiss the picker
    [self dismissModalViewControllerAnimated:YES];
    [[UIApplication sharedApplication] setStatusBarHidden:NO withAnimation:UIStatusBarAnimationFade];

    // Assign the selected item(s) to the music player and start playback.
    [self.musicPlayer stop];
    [self.musicPlayer setQueueWithItemCollection:mediaItemCollection];
    [self.musicPlayer play];

}

- (void)mediaPickerDidCancel:(MPMediaPickerController *)mediaPicker {
    // User did not select anything
    // We need to dismiss the picker
    [self dismissModalViewControllerAnimated:YES];
    [[UIApplication sharedApplication] setStatusBarHidden:NO withAnimation:UIStatusBarAnimationFade];
}

Answer 1

Generally:

1. You should not do any animations in viewWillAppear only in viewDidAppear. Only prepare your data, outlets etc. in viewWillAppear.

2. Also a very common case where wait_fences might arise is when you have an animated dialog (Like your MPMediaPickerController) that causes another animated view to appear (Like a custom modal UIViewController) or the like, in which case you need to “postpone” the presentation of the second viewcontroller like this:

       [self performSelector:@selector(showMyOtherViewController) 
                  withObject:nil 
                  afterDelay:0.1];
   

Also check out this answer https://stackoverflow.com/7194182.

Edit

A good way to “debug” conflicting animations is to simply set the animation to NO so in your code instead of

    [self presentModalViewController:mediaPicker animated:YES];
    [self dismissModalViewControllerAnimated:YES];

Simply do:

    [self presentModalViewController:mediaPicker animated:NO];
    [self dismissModalViewControllerAnimated:NO];

and check if the wait_fences error goes away and the correct behaviour (but without animation) is achieved. If this is the case you need some of the performSelector:withObject:afterDelay:-magic.

Edit: Please note that you can do the following in iOS 5.0:

[self dismissViewControllerAnimated:YES completion:^{
    [self presentViewController:anotherViewController animated:YES completion:NULL]
}

That means that first, the currently presented View Controller (e.g. a ModalViewController) is dismissed and when the animation is finished you can invoke another block. In this case show another UIViewController