No Data Returned Using NSURLConnection Asynchronously

Question

I am having a heck of time with something that seems rather
straightforward but I can't seem to get working. I am building an
iPhone app that retrieves data from a web host. I am trying to
establish an asynchronous connection to the host as I want to keep the
device freed up during the connection. (sendSynchronousRequest freezes
the phone until the request is done.) Here is my connection code:

//temp url to see if data is returned:
NSURL *theURL = [NSURL URLWithString:@"http://www.theappleblog.com/feed"];

NSURLRequest *dataRequest = [NSURLRequest requestWithURL:theURL
             cachePolicy:NSURLRequestReloadIgnoringLocalCacheData
             timeoutInterval:60];

/* establish the connection */  
theConnection = [[NSURLConnection alloc]
                 initWithRequest:dataRequest
                        delegate:self
                startImmediately:YES];

if (theConnection == nil) { 
    NSLog(@"Connection Failure!");
    self.urlData = nil; 
} else {
    self.urlData = [[NSMutableData data] retain];   
}

I have all of the appropriate delegate methods set up:

-(void)connection:(NSURLConnection *)connection
       didReceiveResponse:(NSURLResponse*)response
{
    [urlData setLength:0];
    UIApplication *application = [UIApplication sharedApplication];
    application.networkActivityIndicatorVisible = YES;
    NSLog(@"Received Response!");
}

-(void)connection:(NSURLConnection *)connection
       didReceiveData:(NSData*)incrementalData
{
    [self.urlData appendData:incrementalData];

    NSNumber *resourceLength = [NSNumber
              numberWithUnsignedInteger:[self.urlData length]];
    NSLog(@"resourceData length: %d", [resourceLength intValue]);
    NSLog(@"filesize: %d", self.urlDataSize);
    NSLog(@"float filesize: %f", [self.urlDataSize floatValue]);
}

-(void)connectionDidFinishLoading:(NSURLConnection*)connection
{
    NSLog(@"Connection finished loading\n");
    NSLog(@"Succeeded! Received %d bytes of data",[urlData length]);
    _isFinished = YES;
    UIApplication *application = [UIApplication sharedApplication];
    application.networkActivityIndicatorVisible = NO;
}

- (void)connection:(NSURLConnection *)connection
        didFailWithError:(NSError *)error
{
    NSLog(@"Error: %@",[error localizedDescription]);
}

As you can see, I've got a boat-load of log messages because I wanted
to see if anything was coming through at all. My connection test
comes back as TRUE but no data ever gets loaded. Like I said, I'm sure
I must be doing (or not doing) something really stupid. But what?
Any help would be most appreciated.

Thanks, Lawrence

Answer 1

The problem was that I was continuing program flow and not stopping to allow the connection to finish downloading. Thank you for all of the suggestions.

Answer 2

A few suggestions:

• In your first snippet, instead of theConnection try assigning to self.theConnection to make sure the property accessor methods are called. In various places you also interchange self.urlData and urlData. Might want to make them all consistent by going through self.

• You may want to make the dataRequest a property as well and go through self to make sure it gets retained.

• self.urlData = [[NSMutableData data] retain]; -- you shouldn't need that extra retain. Going through self does it for you. The extra retain will make it so the object will stick around and leak even when all is done.

• On a related note, in your NSLogs make sure you print out the retain count for each object. Also, you may want to have a general clean-up routine around to release these structures (or sets self.foo = nil) so at any point if it barfs out you can call the routine to get things cleaned up.

• Get a copy of Charles or WireShark (or run tcpdump in the console) and watch the network traffic. It'll help pinpoint at what stage in the flow it's failing.