Let’s say you’re making HTTP requests and handling responses as we described last time. Parsing the results is usually pretty easy, but what happens when you have a large blob of data, be it XML or JSON or whatever? Any lengthly processing on the main thread, more than a couple hundred milliseconds, will introduce a noticeable hiccup in the UI. Adding a worker thread would help, but perhaps the easiest method is to use the non-blocking NSOperationQueue. With NSOperationQueue you simply package up the work to be done into an NSOperation instance and add it to the queue.
Your application can create any number of NSOperationQueue objects, but the documentation suggests there is a practical limit to how many operations are executing at any given time. Specifically, adding additional queues does not mean you can execute additional operations. I find that a single queue is usually sufficient. Having access to a global operation queue means you can add, suspend, and cancel operations as needed. Add something like this to ApplicationDidFinishLaunching:
// Create the shared operation queue
sharedOperationQueue = [[NSOperationQueuealloc] init];
id delegate = self;
myConnectionController* connectionController = [[[myConnectionController alloc] initWithDelegate:delegate
selSucceeded:@selector(connectionSucceededWrapper:)
selFailed:@selector(connectionFailed:)] autorelease];
[myConnectionController startRequestForURL:[NSURLURLWithString:@"http://request.org/somequery.php"]];
Notice all we did was change the selSucceeded selector to connectionSucceededWrapper:. The new wrapper method creates and adds the operation to the queue, as follows:
- (void)connectionSucceededWrapper:(NSMutableData*)data
{
NSInvocationOperation* theOp = [[NSInvocationOperation alloc] initWithTarget:self
selector:@selector(connectionSucceeded:) object:data];
[sharedOperationQueue addOperation:theOp];
}
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