dispatch_sync block my UI, I cant click any button

Question

I have 2 blocks with dispatch_sync, when the first block ends I show the window for the user and starts run the second block. But I'm not getting click any button on the screen until the second block ends..

Look the code:

[HUD showUIBlockingIndicatorWithText:@"Loading..."];
dispatch_queue_t queue = dispatch_queue_create("myQueue", DISPATCH_QUEUE_CONCURRENT);
dispatch_async(queue, ^ {
        dispatch_sync(dispatch_get_main_queue(), ^{
                [UIView beginAnimations:@"fade" context:nil];
                [UIView setAnimationDuration:0.5];
                self.capa.alpha = 0.0;
                [UIView commitAnimations];
                [HUD hideUIBlockingIndicator];
        });
});

dispatch_barrier_async(queue, ^ {
    //code executed in the background
    dispatch_async(dispatch_get_main_queue(), ^{
        NSLog(@"entrou na foto");
        //[self getFotos];
    });
});

Answer 1

If you call any code on the main thread, it will block your UI, so calling

dispatch_async(dispatch_get_main_queue(), ^{
    NSLog(@"entrou na foto");
    [self getFotos];
});

will block your UI until [self getFotos] has returned.