Problems with uiimageview.image

Question

Hello!

I want to change an uiimage.image by calling a method in my viewcontroller:

-(void) aendereBild: (NSData*)bildngage {
    UIImage *uiimageAusData = [UIImage imageWithData: bildngage];
    drawImage.image = uiimageAusData;
}

To make it short: The image is not changing. This is not due to the NSData I pass (which i first thought was the problem). This method is called from the appdelegate.

In another void in this viewcontroller I can change the image with drawimage.image = otherimage without any problems, so I think the call from the AppDelegate is causing the problem. Anyone an idea what I did wrong? Thankie!

Answer 1

I think @tonclon has it right that the call from the appDelegate isn't happening in the right thread. An easy way to check is to put a breakpoint on the line that works and the line that doesn't and look at what thread is being used (shown in the Xcode debugger).

This question shows you how you do the update in the right thread if that's the case:

http://stackoverflow.com/questions/805410/how-do-i-update-the-ui-in-the-middle-of-this-thread

You need something like

  [drawImage performSelectorOnMainThread:@selector(setImage:) withObject:uiimageAusData waitUntilDone:NO];

The threads that make calls onto the appDelegate aren't necessarily the main thread -- you should check. Your app starts with a few threads, even if you didn't make any.