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Editorial Team
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Asked: 2026-05-20T23:21:44+00:00

I’m trying to load an image from a url inside of drawRect: . Our

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I’m trying to load an image from a url inside of drawRect:. Our image-loading code is a method that looks like this: - (void) loadImage:(NSURL*)url done:(void(^)(UIImage*))done;, which creates an asynchronous NSURLConnection and calls back with the image.

So, my code in drawRect: looks like this:

CGContextRef context = UIGraphicsGetCurrentContext()
[service loadImage:url done:^(UIImage * image){
    CGContextDrawImage(context, frame, image.CGImage);
}];

Unfortunately, this doesn’t work. The image is never drawn.

I’ve also tried using synchronous connections ([NSData dataWithContentsOfUrl:]), but it blocks the thread and slows things down unnecessarily. I don’t want to use a UIImageView.

What is the correct way to do this? Thanks!

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1 Answer

  1. Editorial Team

    I think the correct way would either be to load the image beforehand or draw the image as soon as you receive it by either calling “setNeedsDisplayInRect:” or doing your own drawing handling in a separate method (iOS might discourage you from doing this though, I am not sure). Obviously the setNeedsDisplayInRect variation would require you to have the image at hand for drawing the second time around (cache it).

    If you load the image asynchronously your drawRect method will moste likely have exited before the image is loaded and the draw focus is no longer locked on your drawRect, thus making it impossible to draw the image in the context. Did you try to set a breakpoint to verify this though? I might be wrong about the locking, but thought I read something alike this at some point.

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