iOS, ARC: Background thread freezes UI

Question

I have a UIViewController with a UITableView as subview. When a certain cell was clicked an UIImagePickerController should be presented. Because of the long initialization time it takes, I perfom this process in the background when the UIViewController did appear.
Now I added ARC to my project and then it didn't still work. The UI was freezed by the initial process.

Here's my code.

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];

    [self performSelectorInBackground:@selector(initImagePickerControllerInBackground) withObject:nil];
}

...

- (void)initImagePickerController
{
    if (imagePickerController != nil)
        return;

    imagePickerController = [[UIImagePickerController alloc] init];
    imagePickerController.allowsEditing = YES;
    imagePickerController.delegate = self;
    imagePickerController.mediaTypes = [NSArray arrayWithObject:(NSString *)kUTTypeImage];
}

- (void)initImagePickerControllerInBackground
{
    @autoreleasepool
    {
        [self initImagePickerController];
    }
}

What should I change to get it working for me?

Answer 1

UIKit is not a thread safe class and should not be called from outside the main thread. You should not perform this UIImagePickerController allocation/interaction in the background.