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    <p>A couple possibilities here.</p> <p>1)</p> <p>How about [NSObject performSelectorOnMainThread: ...] ?</p> <p>E.G.</p> <pre><code>-(void) doNotification: (id) thingToPassAlong { [[NSNotificationCenter defaultCenter] postNotificationName:kImageSavedSuccessfully object:thingToPassAlong]; } -(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) { [self performSelectorOnMainThread: @selector(doNotification:) withObject: self waitUntilDone: YES]; } }); }); } </code></pre> <p>More details at <a href="http://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/Reference/Reference.html#//apple_ref/occ/instm/NSObject/performSelectorOnMainThread:withObject:waitUntilDone" rel="nofollow noreferrer">http://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/Reference/Reference.html#//apple_ref/occ/instm/NSObject/performSelectorOnMainThread:withObject:waitUntilDone</a>:</p> <p>or 2)</p> <p>Completion Callbacks</p> <p>as seen at <a href="https://stackoverflow.com/questions/3379008/how-can-i-be-notified-when-a-dispatch-async-task-is-complete">How can I be notified when a dispatch_async task is complete?</a></p>
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    1. POHow do I post a NSNotification when using Grand Central Dispatch?
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    1. USMichael Dautermann
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    1. POHow do I post a NSNotification when using Grand Central Dispatch?
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    1. COI think the simplicity of your first option is amazingly clean and clear. I was not aware of performSelectorOnMainThread:. What a great way to point out of the sub-thread and perform work in the main loop. Very good. Thx.
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    2. CODoes the code in the original question not work? It looks like it should function as intended, since you're dispatching the notification to the main queue at the end of the block passed to `myQueue`. I prefer this pattern over using `performSelector:onMainThread:` since you're not writing a separate method just to handle your notification. Cleaner code IMO.
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    3. COSo Im confused now with all the options. NSNotificationCenter, GrandCentralDispatch-Blocks & performSelectorOnMainThread. I have used pSOMT with an NSOperation & Queue, but never the first two. Can someone please explain the differences or advantages?
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      1. USmarciokoko
 

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