dispatch_async and NSURLConnection

[WillshawMedia]

I'm really struggling with an app I'm writing at the moment.

I've got some intense string manipulation, which I'm performing inside a dispatch_async block.

At the end of the block I've got a dispatch_async(dispatch_get_main_queue()) block, which calls a custom function: getPrices();

Inside getPrices() I use an NSURLConnection. The delegate methods are not being called, my connection is made, but I don't get a fail, success, authentication challenge, anything at all.

The code looks like this:

- (void)performSearch {

    // set some defaults and work out if it is a valid search, setting bSearchOk

    if (bSearchOk) {

        // update some interface elements
        self.msgBox.text = @"Translating...";            
        self.plateInput.enabled = NO;
        self.searchProgress.hidden = NO;

        dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

            // create a new search
            Search *oPlateSearch = [[Search alloc] initWithTerm:thisTerm];

            // ...
            // perform search... this calls a variety of slow and intensive functions
            // ...

            self.aFinalPlates = [oPlateSearch.aValidated copy];
            self.aCurrentPlates = [oPlateSearch.aFinals copy];        

            dispatch_async( dispatch_get_main_queue(), ^{                 
                [oPlateSearch release];              

                // make ajax call to check if plates can be bought
                [self getPrices];                 
            });
        });

    } else {
        // hide results
        self.searchResults.hidden = YES;
    }

}

And this is getPrices()

/* call to get plate availability and prices */
-(void) getPrices {
    // set return message
    self.msgBox.text = @"Getting prices and availability";

    // ...
    // then I build my strRequest var, which is a valid working URL
    // ...

    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:strRequest]];

    NSURLConnection *loginConnection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
[loginConnection scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
[loginConnection start];

    NSLog('This will get logged');

    if(loginConnection) {
        NSLog('This will also get logged');
        self.jsonSearchResponse = [[[NSMutableData data] retain] autorelease];
        NSLog('And this will get logged, so it's not throwing errors');
    } else {
        NSLog(@"Failed to get search results");
    }
}

Any ideas what I'm doing wrong?

[Duncan C]

Originally Posted by WillshawMedia

I'm really struggling with an app I'm writing at the moment.

I've got some intense string manipulation, which I'm performing inside a dispatch_async block.

At the end of the block I've got a dispatch_async(dispatch_get_main_queue()) block, which calls a custom function: getPrices();

Inside getPrices() I use an NSURLConnection. The delegate methods are not being called, my connection is made, but I don't get a fail, success, authentication challenge, anything at all.

The code looks like this:

- (void)performSearch {

    // set some defaults and work out if it is a valid search, setting bSearchOk

    if (bSearchOk) {

        // update some interface elements
        self.msgBox.text = @"Translating...";            
        self.plateInput.enabled = NO;
        self.searchProgress.hidden = NO;

        dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

            // create a new search
            Search *oPlateSearch = [[Search alloc] initWithTerm:thisTerm];

            // ...
            // perform search... this calls a variety of slow and intensive functions
            // ...

            self.aFinalPlates = [oPlateSearch.aValidated copy];
            self.aCurrentPlates = [oPlateSearch.aFinals copy];        

            dispatch_async( dispatch_get_main_queue(), ^{                 
                [oPlateSearch release];              

                // make ajax call to check if plates can be bought
                [self getPrices];                 
            });
        });

    } else {
        // hide results
        self.searchResults.hidden = YES;
    }

}

And this is getPrices()

/* call to get plate availability and prices */
-(void) getPrices {
    // set return message
    self.msgBox.text = @"Getting prices and availability";

    // ...
    // then I build my strRequest var, which is a valid working URL
    // ...

    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:strRequest]];

    NSURLConnection *loginConnection = [[NSURLConnection alloc] initWithRequest:request delegate:self startImmediately:NO];
[loginConnection scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
[loginConnection start];

    NSLog('This will get logged');

    if(loginConnection) {
        NSLog('This will also get logged');
        self.jsonSearchResponse = [[[NSMutableData data] retain] autorelease];
        NSLog('And this will get logged, so it's not throwing errors');
    } else {
        NSLog(@"Failed to get search results");
    }
}

Any ideas what I'm doing wrong?

Call your getPrices method using preformSelectorOnMainThread.

Make getPrices simply call [connection start] without using scheduleInRunLoop.

Set your object to be the delegate of the connection, so you get callbacks as the download progresses.

[WillshawMedia]

Originally Posted by Duncan C

Call your getPrices method using preformSelectorOnMainThread.

Make getPrices simply call [connection start] without using scheduleInRunLoop.

Set your object to be the delegate of the connection, so you get callbacks as the download progresses.

I don't think I fully understand the documentation for performSelectorOnMainThread.

I've tried this:

 [self performSelectorOnMainThread:getPrices withObject:Nil waitUntilDone:NO];

But I'm getting the error: "Use of undeclared identifier getPrices". The docs say that parameter should be a "selector that identifies the method to invoke" and I want to invoke getPrices.

I thought delegate:self was already setting the delegate to be the object calling the method? Is that not right?

[apatsufas]

The appropriate syntax for performSelectorOnMainThread is

- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait

in your case that would be

 [self performSelectorOnMainThread:@selector(getPrices) withObject:Nil waitUntilDone:NO];

[WillshawMedia]

Originally Posted by apatsufas

in your case that would be

 [self performSelectorOnMainThread:@selector(getPrices) withObject:Nil waitUntilDone:NO];

That fixed it, that was perfect. Thanks to both of you for helping!