NSURLRequest with caching not working

Question

I am trying to cache my nsurlrequest data. Prior to this i was successfully downloading data from the server, ever since I tried to implement this cache its been making my application fall over. Im hoping someone can look at the code i have so far and help me to get it workig.. I think I have roughly 95% of it done.

- (IBAction)setRequestString:(NSString *)string
{
    //Set database address
    NSMutableString *databaseURL = [[NSMutableString alloc] initWithString:@"http://127.0.0.1:29/"]; // imac development


    //PHP file name is being set from the parent view
    [databaseURL appendString:string];

    //call ASIHTTP delegates (Used to connect to database)
    NSURL *url = [NSURL URLWithString:databaseURL];

    //SynchronousRequest to grab the data, also setting up the cachePolicy
    NSURLRequest *request = [NSURLRequest requestWithURL:url cachePolicy:NSURLRequestReturnCacheDataElseLoad timeoutInterval:60.0]; //if request dose not finish happen within 60 second timeout.

    //This nsdata will be used to put the cache into
    NSData *cacheData = [[NSData alloc] init];
    //Create my own NSCachedURLResponse and add it to the cache
    NSURLResponse *responseToCache = [[NSURLResponse alloc] initWithURL:url MIMEType:@"text/xml" expectedContentLength:[cacheData length] textEncodingName:nil];
    //Set up the cache
    NSCachedURLResponse *cacheResponse = [[NSCachedURLResponse alloc] initWithResponse:responseToCache data:cacheData];
    [[NSURLCache sharedURLCache] storeCachedResponse:cacheResponse forRequest:request];

    //check if its really there
    NSLog(@"cache = %@", [[NSURLCache sharedURLCache] cachedResponseForRequest:request]);


    //If no cache do this stuff, connect to the db and perform these actions. I think this is what i am supposed to be doing.
    NSOperationQueue *queue = [[NSOperationQueue alloc] init];
    [NSURLConnection sendAsynchronousRequest:request queue:queue completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
    {
        if ([data length] > 0 && error == nil){
            [self receivedData:data];
        }else if ([data length] == 0 && error == nil){
            [self emptyReply];
        }else if (error != nil && error.code == NSURLErrorTimedOut){
            [self timedOut];
        }else if (error != nil){
            [self downloadError:error];
        }
    }];
}

Answer 1

Follow this link for an dead simple way of doing this using a category method on NSURLConnection. It's for asynchronous requests but can be adapted easily for synchronous ones.

Also I strongly advise that you use a private property or instance variable for your NSOperationQueue so that all your requests use the same operation queue.