Asynchronous URLRequest methods within the same class...

[pdd]

I have an application that needs to make a handful of web service calls. Here's how I get to the problem.

First, my app (from a modal view controller) calls a "DataServices" class I created to handle the web service calls. There can be anywhere from one to many web service calls inside the Data Services class.

I have an array of strings representing ID's of objects to be downloaded.

NSArray *list = [[NSArray alloc] initWithObjects:@"1", @"2", @"3", nil];

Then, I loop through this array.

for (NSString *item in list) {
    [self callWebService:item];
}

Then, the callWebService function is called.

- (void)callWebService:(NSString *)item
{
    // Soap message defined properly
    NSURL *url = [NSURL URLWithString:webServiceBaseAddress];
    NSMutableURLRequest *request  = [NSMutableURLRequest requestWithURL:url];
    NSString *length = [NSString stringWithFormat:@"%d", [soapMessage length]];
                        
    [request addValue:@"application/soap+xml; charset=utf-8" forHTTPHeaderField:@"Content-Type"];
    [request addValue:length forHTTPHeaderField:@"Content-Length"];
    [request setHTTPMethod:@"POST"];
    [request setHTTPBody:[soapMessage dataUsingEncoding:NSUTF8StringEncoding]];
    
    NSURLConnection *connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
    
    if (connection) {
        webData = [[NSMutableData data] retain];
    } else {
        NSLog(@"Connection is null.");
    }
}

And then I've defined didReceiveResponse, didReceiveData, didFailWithError, and connectionDidFinishLoading.The web service code works fine, because when there is one item in the array, it downloads perfectly. When there is more than one item in the loop, though, the web service call bumps into itself. It's operating asynchronously, and then returning EXC_BAD_ACCESS errors because of the thread conflicts, I'm guessing.

So, is there a way I can make sure the [self callWebService:item] method COMPLETES before moving to the next item in the loop?

Thanks for the help!

[baja_yu]

Don't call them all in a loop. Call the webservice only for the first item in the array, then when it completes (in delegate methods), remove that item from the array, and if there are other items still in it, call the service for the next one. That way it will loop through them all one by one.

[pdd]

Originally Posted by baja_yu

Don't call them all in a loop. Call the webservice only for the first item in the array, then when it completes (in delegate methods), remove that item from the array, and if there are other items still in it, call the service for the next one. That way it will loop through them all one by one.

I implemented that this morning, and it works great.

But, is there a better way to make the method execute synchronously? NSOperationQueue or something like that?

[baja_yu]

You could try that as well, Loading… see the setMaxConcurrentOperationCount to set how many operations can run at the same time. It notes:

Note: Setting the maximum number of operations to 1 effectively creates a serial queue for processing operations.