Get image Asynchronously and setting setNeedsDisplay - objective-c

Question

This code is in in a cell initialization routine that sets up the elements of a custom cell. It gets the image from the web asynchronously. But I need it to redraw once it's done.
This is my snippet of code:
dispatch_async(myCustomQueue, ^{
//Look for the image in a repository, if it's not there
//load the image from the web (a slow process) and return it
mCover.image = [helperMethods imageManagerRequest:URL];
//Set the image to be redrawn in the next draw cycle
dispatch_async(dispatch_get_main_queue(), ^{
[mCover setNeedsDisplay];
});
});
But it doesn't redraw the UIImageView. I've tried to also redraw the entire cell, and that doesn't work either. Your help is much appreciated. I've been trying to fix this for some time!

Answer 1

Instead of setNeedsDisplay, you should set the image on main thread as Apple have mentioned in their documentation.
Note: For the most part, UIKit classes should be used only from an
application’s main thread. This is particularly true for classes
derived from UIResponder or that involve manipulating your
application’s user interface in any way.
This should fix your problem:
dispatch_async(myCustomQueue, ^{
//Look for the image in a repository, if it's not there
//load the image from the web (a slow process) and return it
UIImage *image = [helperMethods imageManagerRequest:URL];
//Set the image to be redrawn in the next draw cycle
dispatch_async(dispatch_get_main_queue(), ^{
mCover.image = image;
});
});