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.
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.
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:
NOTIFICATION: the asset library changed // my own NSLog for when the notification occurs
loading assets... // my own NSLog for when I start reloading assets in the thumbnail browser
Assertion failed: (size == bytesRead), function -[ALAssetRepresentation _imageData], file /SourceCache/AssetsLibrary/MobileSlideShow-1373.58.1/Sources/ALAssetRepresentation.m, line 224.
The specific line of code it crashes on, is in calling [currentRep metadata] as shown here:
NSURL *assetURL = [self.assetURLsArray objectAtIndex:index];
ALAsset *currentAsset;
[self.assetsLibrary assetForURL:nextURL resultBlock:^(ALAsset *asset) {
currentAsset = asset;
} failureBlock:^(NSError *error) {
NSLog(@"failed to retrieve asset: %@", error);
}];
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");
}
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?
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:
if (self.receivedLibraryChangeNotification) {
NSLog(@"received library change notification, need to abort");
}
else {
metaDictionary = [currentRep metadata];
}
Is there anything I can do? At this point I'm almost ready to give up on using the ALAssetsLibrary framework.
(note this unresolved thread on the Apple dev forums describing the same issue: https://devforums.apple.com/message/604430 )
