Question

I can successfully retrieve data asynchronously through NSURLConnection from any other part in the code base except in the canDrawMapRect function in my subclassed TileOverlayView class.

I’m modifying the MapKit sample called tileMap to download tiles from a server and overlay that information on the map. In the canDrawMapRect I call a function in the overlay class which in turn creates the url and opens up a connection. I have already tested my connection class and have confirmed that it does indeed work. I’ve run it in the init functions of overlay and overlayView with success. The urls are good too since I can throw them in a browser and they show the right pngs. I know that canDrawMapRect is running on multiple threads and I only have novice experience with threads.

Here is my connection code,

- (id)initWithStringUrl: (NSString*) url {

    NSLog(@"Test Connect Init URL %@", url);

    self = [super init];
    if (self)
    {
        [self loadURL:[NSURL URLWithString:url]];    
    }

    return self;
}
+ (UIImage*)connectSynchronousWithURL:(NSString*) url {
    NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:url]];

    NSURLResponse* response = [[NSURLResponse alloc] init];
    NSError* error = [[NSError alloc] init];
    NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];
    UIImage *image = [UIImage imageWithData: data];

    return image;
}
- (BOOL)loadURL:(NSURL *)inURL {
    NSURLRequest *request = [NSURLRequest requestWithURL:inURL];
    NSURLConnection *conn = [NSURLConnection connectionWithRequest:request delegate:self];

    if (conn) {
        receivedData = [[NSMutableData data] retain];
        NSLog(@"Connection Success");
    } else {
        NSLog(@"Connection Failed");        
        return FALSE;
    }

    return TRUE;
}
- (void)connection:(NSURLConnection *)conn didReceiveResponse:(NSURLResponse *)response {
    NSLog(@"didReceiveResponse");
    [receivedData setLength:0]; 
}
- (void)connection:(NSURLConnection *)conn didReceiveData:(NSData *)data {
    NSLog(@"didReceiveData");
    [receivedData appendData:data];
}

- (void)connectionDidFinishLoading:(NSURLConnection *)conn {
    NSLog(@"Succeeded! Received %d bytes of data", [receivedData length]);
}

Pretty standards stuff. If I run the code in the init of TileOverlayView it’ll work just fine but if I run it in canDrawMapRect then none of the delegate functions get called. I suppose it’s also worth mentioning that the synchronous connection to the server does work in the canDrawMapRect method. I don’t get it at all T_T

Any help would be greatly appreciated. Thank you.

Answer 1

From the docs about NSURLConnection, this pretty much sums it up.

Note that these delegate methods will be called on the thread that started the asynchronous load operation for the associated NSURLConnection object.

Looks like I’ll be needing to use CFRunLoopRun() and CFRunLoopStop(CFRunLoopGetCurrent()); to keep the thread alive. Or find an alternative to making these async calls in the thread.