Second asynchronous NSURLConnection doesn't call delegate methods

Question

From my ApplicationDelegate, I'm doing an NSURLConnection fetch over the network (it's wrapped in a class, as you'll see below). This one seems to work correctly: I get all the data in didReceiveData and I get the completion call connectionDidFinishLoading. At the end of connectionDidFinishLoading, I instantiate one or more of a slightly different kind of wrapper class, but they're essentially the same thing. The problem is that the second NSURLConnection's delegate is never having it's methods called.

I've looked at many different answers, but all to no avail. I'm not spawning any new threads and all the [NSThread isMainThread] checks I've littered throughout the code return true.

I'm stumped. Can anyone help me out? Here's the relevant code:

App Delegate:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

    ConnectionWrapper* w = [[ConnectionWrapper alloc] initWithParams:self
    url:[NSURL URLWithString:<url>]];
[w beginFetch];

    return YES;
}

...

-(void)fetchCompleted:(NSURL*)url directory:(NSString*)directory
{
NSLog(@"fetch completed");
}

-(void)fetchFailed:(NSURL*)url
{
NSLog(@"fetch failed");
}

...

ConnectionWrapper:

-(id)initWithParams:(id<ConnectionWrapperDelegate>)d url:(NSURL*)url
{
    delegate = d;

    connURL = url;

    return [self init];
}

-(void)beginFetch
{
    NSURLRequest* request = [[NSURLRequest alloc] initWithURL:connURL];
    NSURLConnection* conn = [[NSURLConnection alloc] initWithRequest:request delegate:self];

    [conn release];
    [request release];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    NSLog(@"append");
    [responseData appendData:data];
}

- (void) connectionDidFinishLoading: (NSURLConnection*) connection
{
    ... parsing ....

    DifferentConnectionWrapper* w = [[DifferentConnectionWrapper alloc] initWithParams:self
        url:[NSURL URLWithString:<different url>]];
    [w beginFetch];
}

-(void)fetchCompleted:(NSURL*)URL
{
    NSLog(@"completed: %@", URL);
}

-(void)fetchFailed:(NSURL*)URL
{
    NSLog(@"failed");
}

DifferentConnectionWrapper:

-(id)initWithParams:(id)d url:(NSURL*)url { delegate = d;

    connURL = url;

    return [self init];
}

-(void)beginFetch
{
    NSURLRequest* request = [[NSURLRequest alloc] initWithURL:connURL];
    NSURLConnection* conn = [[NSURLConnection alloc] initWithRequest:request delegate:self];

    [conn release];
    [request release];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    NSLog(@"append");
    [responseData appendData:data];
}

- (void) connectionDidFinishLoading: (NSURLConnection*) connection
{
    ... parsing ....

    DifferentConnectionWrapper* w = [[DifferentConnectionWrapper alloc] initWithParams:self
        url:[NSURL URLWithString:<different url>]];
    [w beginFetch];
}

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    NSLog(@"got response");
    [responseData setLength:0];
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    NSLog(@"got data");
    [responseData appendData:data];
}

- (void) connectionDidFinishLoading: (NSURLConnection*) connection
{
    NSLog(@"image saver completed: %@", connURL);
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    NSLog(@"error");
}

ConnectionWrapper and DifferentConnectionWrapper have similar functions, but there's other logic that I've omitted here for brevity.

thanks for the help. I appreciate it.

Answer 1

OK. It turns out that this bug was caused by something I missed. I was going into a hard spin right after that second request, which would probably screw up just about anything. Once I fixed that problem, everything worked just fine.

Thanks for the help.

Answer 2

I believe the problem is that you’re releasing the URL connection in -beginFetch:

-(void)beginFetch
{
    NSURLRequest* request = [[NSURLRequest alloc] initWithURL:connURL];
    NSURLConnection* conn = [[NSURLConnection alloc] initWithRequest:request delegate:self];

    [conn release];
    [request release];
}

The URL connection object should be kept alive and released when the connection has finished loading:

- (void) connectionDidFinishLoading: (NSURLConnection*) connection
{
    ... parsing ....

    // *** Release the connection and whatever data you’ve kept related to
    // this particular connection
    [connection release];
    [responseData release];
    // *** or [responseData setLenght:0]; depending on how you’re
    // managing responseData

    DifferentConnectionWrapper* w = [[DifferentConnectionWrapper alloc] initWithParams:self
        url:[NSURL URLWithString:<different url>]];
    [w beginFetch];
}

or when there’s been an error:

- (void)connection:(NSURLConnection *)connection
  didFailWithError:(NSError *)error
{
    // *** Release the connection and whatever data you’ve kept related to
    // this particular connection
    [connection release];
    [responseData release];
    // *** or [responseData setLenght:0]; depending on how you’re
    // managing responseData

    // inform the user
    NSLog(@"Connection failed! Error - %@ %@",
          [error localizedDescription],
          [[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);
}

---

Edit: Your initialiser is a tad weird:

-(id)initWithParams:(id<ConnectionWrapperDelegate>)d url:(NSURL*)url
{
    delegate = d;    
    connURL = url;
    return [self init];
}

There’s no way to know what happens unless we see the code for -init and, at any rate, this should be the designated initialiser, so it shouldn’t be sending -init to self anyway. Furthermore, you should be retaining the url object that’s being passed to the initialiser.

The following makes more sense:

-(id)initWithParams:(id<ConnectionWrapperDelegate>)d url:(NSURL*)url
{
    self = [super init];
    if (self) {
        delegate = d;    
        connURL = [url retain];
    }
    return self;
}

Don’t forget to release the url object in -dealloc or when you’re assigning another value to connURL.

Answer 3

A couple of things: I don't see a didFailWithError: in your first wrapper class, and (a little off topic) are you leaking memory with your DifferentConnectionWrapper *w ?

Anyway, what I would try is: see if you can invoke DifferentConnectionWrapper directly from the appDelegate instead of the ConnectionWrapper. And I would try to decouple the two calls in any event. When the first one finishes, and calls appDelegate, can't you launch your DifferentConnectionWrapper from there?

I realize this doesn't explain your problem, but you might get it working (and which of THOSE two things is more important, is an entirely different debate.)