Parse Two (YouTube) JSON links at once - ios

Question

I am having an issue parsing two JSON urls at once. YouTube only permits 50 results per request, so I'd like to add a second with a start-index of 51, to continue the request.
NSString *urlAsString = #"https://gdata.youtube.com/feeds/api/playlists/PLgw1uRYia2CRvuF4Y3KLuvFSWY6lmuY8T?v=2&alt=json&max-results=50&orderby=published";
NSString *urlAsString2 = #"https://gdata.youtube.com/feeds/api/playlists/PLgw1uRYia2CTSBBNrTDjdEcswVFjPkCr9?v=2&alt=json&max-results=50&orderby=published";
Combining two of them, I tried this:
NSString *finallink = [NSString stringWithFormat:#"%#,%#", urlAsString, urlAsString2];
Then making the actual request with Afnetworking, I added:
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
[manager GET:finallink parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
manager.requestSerializer = [AFHTTPRequestSerializer serializer];
manager.responseSerializer = [AFHTTPResponseSerializer serializer];
NSDictionary *feed = [[NSDictionary alloc] initWithDictionary:[responseObject valueForKey:#"feed"]];
videoArray = [NSMutableArray arrayWithArray:[feed valueForKey:#"entry"]];
[self.videoMetaData addObjectsFromArray:[videoArray valueForKeyPath:#"title.$t"]];
operation.responseSerializer.acceptableContentTypes = [NSSet setWithObject:#"text/html"];
[self.videolist reloadData];
[self->activityind startAnimating];
NSLog(#"JSON: %#", responseObject);
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:#"Error Retrieving Videos"
message:[error localizedDescription]
delegate:nil
cancelButtonTitle:#"Ok"
otherButtonTitles:nil];
[alertView show];
NSLog(#"Error: %#", error);
}];
This does not work for some reason. I get this error:
Error: Error Domain=NSCocoaErrorDomain Code=3840 "The operation couldn’t be completed. (Cocoa error 3840.)"
What could be wrong?!

Answer 1

As mentioned in the comments, this code fails because you are trying to retrieve the result of two URLs joined to one another. The way it is set up now is equivalent to trying to visit http://google.com,http://google.com in a web browser, which will of course fail.
Instead, the solution is to retrieve the results in batches, one after the other. Here's one way to do it:
Write a method which retrieves the YouTube results at a given offset. If you want to retrieve all links starting at 51, then a good idea would be to have a method which takes an offset and returns the results in a completion block.
Write another method which can use the previous one to retrieve the entire list of results. This will need to send multiple network requests to YouTube, one for each batch of 50 that you need, and collect the results somewhere.
There are a couple other issues I noticed in your code sample. One is that you are setting a new request and response serializer in the success block of your network request – instead, you should set these once somewhere in your app, because reallocating them after each request is inefficient. AFHTTPRequestOperationManager does create default instances of these, so you can get away with not setting them at all.
Another potential issue is that you are displaying an alert view in your failure block. Because AFNetworking performs network requests on a background thread by default (from what I recall), you might run into some weird problems (the usual symptom is that your UI will not show up for a few seconds). Apple requires that UI-related methods are called on the main thread.