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POALAssetsLibrary - crash after receiving ALAssetsLibraryChangedNotification
 

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    <p>Part of my app has a photo browser, somewhat similar to Apple's Photos app, with an initial view controller to browse photo thumbnails and a detail view that's shown when you tap on a photo.</p> <p>I'm using ALAssetsLibrary to access photos, and I pass an array of ALAsset URL's to my detail view controller so you can swipe from one photo to the next.</p> <p>Everything works great, until I receive an ALAssetsLibraryChangedNotification while swiping from one photo to another (in the detail view controller), which often results in a crash:</p> <blockquote> <p>NOTIFICATION: the asset library changed // my own NSLog for when the notification occurs</p> <p>loading assets... // my own NSLog for when I start reloading assets in the thumbnail browser</p> <p>Assertion failed: (size == bytesRead), function -[ALAssetRepresentation _imageData], file /SourceCache/AssetsLibrary/MobileSlideShow-1373.58.1/Sources/ALAssetRepresentation.m, line 224.</p> </blockquote> <p>The specific line of code it crashes on, is in calling [currentRep metadata] as shown here:</p> <pre><code>- (void)someMethod { NSURL *assetURL = [self.assetURLsArray objectAtIndex:index]; ALAsset *currentAsset; [self.assetsLibrary assetForURL:assetURL resultBlock:^(ALAsset *asset) { [self performSelectorInBackground:@selector(configureDetailViewForAsset:) withObject:asset]; } failureBlock:^(NSError *error) { NSLog(@"failed to retrieve asset: %@", error); }]; } - (void)configureDetailViewForAsset:(ALAsset *)currentAsset { ALAssetRepresentation *currentRep = [currentAsset defaultRepresentation]; if (currentAsset != nil) { // do some stuff } else { NSLog(@"ERROR: currentAsset is nil"); } NSDictionary *metaDictionary; if (currentRep != nil) { metaDictionary = [currentRep metadata]; // do some other stuff } else { NSLog(@"ERROR: currentRep is nil"); } } </code></pre> <p>I understand that once a notification is received, it invalidates any references to ALAsset and ALAssetRepresentation objects... but how am I supposed to deal with the situation where it invalidates something right in the middle of trying to access it?</p> <p>I've tried setting a BOOL, right when receiving the notification to completely abort and prevent [currentRep metadata] from ever being called, but even that doesn't catch it every time:</p> <pre><code>if (self.receivedLibraryChangeNotification) { NSLog(@"received library change notification, need to abort"); } else { metaDictionary = [currentRep metadata]; } </code></pre> <p>Is there anything I can do? At this point I'm almost ready to give up on using the ALAssetsLibrary framework.</p> <p>(note this unresolved thread on the Apple dev forums describing the same issue: <a href="https://devforums.apple.com/message/604430" rel="nofollow noreferrer">https://devforums.apple.com/message/604430</a> )</p>
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