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PONSOperation in iOS - How to handle loops and nested NSOperation call to get Images
 

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    <p>I need help understanding how to appropriate handle the following use case:</p> <p>Say I'm writing a Chat app:</p> <ol> <li>Launch App</li> <li>Ask server (<code>AFHTTPRequestOperation</code>) to give me a list of all new messages</li> <li>Loop through those messages to see if I need to download any images</li> <li>If yes, then make another call to the server (<code>AFImageRequestOperation</code>) to get the image</li> </ol> <p>I keep getting crashes where my managed object "message" is no longer in the same context, but I'm only using one <code>managedObjectContext</code>. </p> <p>Is it because of the way I'm nesting the calls, since they are asynchronous? I am almost positive the message isn't getting deleted elsewhere, because I see it.</p> <p>One thing to note is that is seems to happen when I change view controllers. I launch the app, and at the root view controller (RVC), it performs step #2 above. If I touch to go the the "<code>MessageListViewController</code>" (MLVC) before all of the images have downloaded, the associated messages for those images that didn't finish downloading suddenly have a nil <code>managedObjectContext</code>. </p> <p>Below is the relevant code:</p> <pre><code> AFHTTPRequestOperation * operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:requestImageInfoURL success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) { NSDictionary * JSONresponse = (NSDictionary *)JSON; if( [[[JSONresponse objectForKey:@"status"] uppercaseString] isEqualToString:@"ERROR"] ) { for( id&lt;CommsObserver&gt; observer in _observers ) [observer errorOccurred:[JSONresponse objectForKey:@"message"]]; } else { if( [JSONresponse containsKey:@"convoMessages"] ) { NSArray * messageList = [JSON objectForKey:@"messages"]; for( int i = 0 ; i &lt; messageList.count ; i++ ) { __block ConversationMessage * message = [JSONUtility convoMessageFromJSON:[messageList objectAtIndex:i]]; if( !message ) NSLog( @"Couldn't create the new message..." ); else { message.unread = [NSNumber numberWithBool:YES]; [[DataController sharedController] saveContext]; if( (!message.text || [message.text isEqualToString:@""]) &amp;&amp; (message.image || message.imageInfoKey) ) { NSString * imageURL = (message.image ? [Comms urlStringForImageInfo:message.image] : [Comms urlStringForImageKey:message.imageInfoKey extension:message.imageInfoExt]); NSURLRequest *requestImageURL = [NSURLRequest requestWithURL:[NSURL URLWithString:imageURL]]; AFImageRequestOperation * imageOperation; imageOperation = [AFImageRequestOperation imageRequestOperationWithRequest:requestImageURL imageProcessingBlock:^UIImage *(UIImage *image) { return image; } success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) { if( message.image ) { NSLog( @"updating imageInfo for message" ); [Utilities updateImageInfo:message.image withImage:image asPreview:YES asThumbnail:YES preserveSize:YES]; } else { NSLog( @"creating a new imageInfo for message" ); ImageInfo * imageInfo = [Utilities createImageInfoFromImage:image asPreview:NO asThumbnail:NO preserveSize:YES]; if( imageInfo.managedObjectContext == nil ) NSLog( @"imageInfo MOC is NIL" ); else if( message.managedObjectContext == nil ) { NSLog( @"message MOC is NIL" ); message = [[DataController sharedController] convoMessageForKey:message.key]; if( !message ) NSLog( @"message is NIL, meaning it wasn't found in the MOC" ); else if( !message.managedObjectContext ) NSLog( @"message MOC was STILL NIL" ); else NSLog( @"problem solved..." ); } if( imageInfo ) [[DataController sharedController] associateImageInfo:imageInfo withMessage:message]; } [[DataController sharedController] saveContext]; } failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) { NSLog( @"Image DOWNLOAD error... \n%@" , [NSString stringWithFormat:@"%@" , error] ); }]; [imageOperation start]; } for( id&lt;CommsObserver&gt; observer in _observers ) [observer newConvoMessages:@[message.key]]; } } // End for loop of messageList } // End if JSONresponse } // End outer if ERROR statement } // End Success failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, id JSON) { NSLog( @"Error: \n%@" , [NSString stringWithFormat:@"%@" , error] ); } ]; [operation start]; </code></pre>
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    1. COYou should edit your title, it has nothing to do with AFNetworking.
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    2. CO@CouchDeveloper, good point. Replaced AFNetworking with NSOperation.
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