Cocoa Image Gallery Window

Question

I have a HUD panel in an app and I want to be able to take a set of images and show each image on the panel for a few seconds before displaying the next image. I'm very new to Cocoa and am having trouble implementing this so some pointers would be welcomed. Here's what I'm currently trying:

[newShots enumerateObjectsUsingBlock:^(NSDictionary *obj, NSUInteger idx, BOOL *stop) 
 {
     //get url
     NSURL *imageUrl = [[NSURL alloc] initWithString:[obj objectForKey:@"image_url"]];;

     //get image from url
     NSImage *image = [[NSImage alloc] initWithContentsOfURL:imageUrl];

     //set it to shot panel
     [shotPanelImageView setImage:image]; 

     //clean up
     [imageUrl release];
     [image release];

     //set needs refresh
     [shotPanelImageView setNeedsDisplay:YES];

     //sleep a few before moving to next
     [NSThread sleepForTimeInterval:3.0];
 }]; 

As you can see I'm just looping the info for each image, grabbing it via URL, setting it to the view, and then calling thread sleep for a few seconds before moving on. The issue is that the view will not redraw with the new image when it is assigned. I thought that setNeedsDisplay:YES would force a redraw but only the first image in the collection is ever displayed. I've put in NSLog()'s and debugged and I know for sure the enumeration is working correctly as I can see the new image information being set as it should.

Is there something I'm missing or is this a completely wrong way of going about solving this problem?

Thanks,

Craig