UI got a little stuck since fetching a photo

Question

Now I'm using this code, with a little modification:

if (self._photoPath && !self._photo) {
        dispatch_queue_t bg_thread = dispatch_queue_create("com.yourcompany.bg_thread", NULL);
        dispatch_queue_t main_queue = dispatch_get_main_queue();
        dispatch_async(bg_thread,^{
            NSData *data = [NSData dataWithContentsOfFile:self._photoPath];
            if(data != nil) {
                dispatch_async(main_queue,^{ 
                    self._photo = [UIImage imageWithData:data];
                    [self.photoButton setImage:[UIImage imageNamed:@"photoButton.png"] forState:UIControlStateNormal];
                });
            }
        });

    }

As you can see, in fact after I get that photo I want set it immediately to my "photoButton", but now, UI got smoothed, but my photoButton's appearance is always black...

What should I do next?

_______________________Updated___________________

I have 2 viewControllers, A and B. A is the root viewController, and B is A's child viewController. In B, there is a button for calling the camera to take a photo.

After user took a photo, the photo's appearance becomes that photo.

When I push a new B (with no photo) from A, things goes smoothly. But when there is an old B with a photo in it, the animation gets a little stuck, caused by the following code I guess:

- (void)viewWillAppear:(BOOL) animated {
    if (self._photoPath && !self._photo) {
            NSData *data = [NSData dataWithContentsOfFile:self._photoPath];
            if(data != nil)
                self._photo = [UIImage imageWithData:data];
    }
    [super viewWillApear];
}

But I do need to get that photo before the view is displayed since I need to set that photo to my photoButton's background.

So, is there a way to avoid sticking the view's animation? Because it really result in bad user experience.

Answer 1

Try fetching the photo in a backgroudn thread (I'm using GCD here):

- (void)viewWillAppear:(BOOL) animated {
    if (self._photoPath && !self._photo) {
      dispatch_queue_t bg_thread = dispatch_queue_create("com.yourcompany.bg_thread", NULL);
      dispatch_queue_t main_queue = dispatch_get_main_queue();
      dispatch_async(bg_thread,^{
          NSData *data = [NSData dataWithContentsOfFile:self._photoPath];
          if(data != nil) {
            dispatch_async(main_queue,^{ self._photo = [UIImage imageWithData:data]; });
          }
      });
    }
    [super viewWillApear];
}