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POHow do I post a NSNotification when using Grand Central Dispatch?
 

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  1. POHow do I post a NSNotification when using Grand Central Dispatch?
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    <p>I found that as predicted when I was writing an image to file that my UI was blocked for the duration, which was not acceptable. When I write the image to file I then post an NS Notification so that I can do some other specific jobs related to that completion. Original working but UI blocking code:</p> <pre><code>-(void)saveImageToFile { NSString *imagePath = [self photoFilePath]; BOOL jpgData = [UIImageJPEGRepresentation([[self captureManager] stillImage], 0.5) writeToFile:imagePath atomically:YES]; if (jpgData) { [[NSNotificationCenter defaultCenter] postNotificationName:kImageSavedSuccessfully object:self]; } </code></pre> <p>To avoid the UI blocking I have put the writeToFile: into a Grand Central Dispatch queue so it runs as a concurrent thread. But when the write is completed and the thread is done, I want to post an NSNotification. I cannot as the code is shown here because it is in a background thread. But that is the functionality I want to accomplish, realizing this is not workable code:</p> <pre><code>-(void)saveImageToFile { NSString *imagePath = [self photoFilePath]; // execute save to disk as a background thread dispatch_queue_t myQueue = dispatch_queue_create("com.wilddogapps.myqueue", 0); dispatch_async(myQueue, ^{ BOOL jpgData = [UIImageJPEGRepresentation([[self captureManager] stillImage], 0.5) writeToFile:imagePath atomically:YES]; dispatch_async(dispatch_get_main_queue(), ^{ if (jpgData) { [[NSNotificationCenter defaultCenter] postNotificationName:kImageSavedSuccessfully object:self]; } }); }); } </code></pre> <p>What is the correct mechanism here to post this notification to gain the functionality I want ?</p>
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