Is this the right way of using NSOperation (AFXMLRequestOperation)? - ios

Question

In my app I have a series of background tasks to be performed one after the other (say tasks : A, B and C). Each of these tasks talk to different web services (XML). I am using AFXMLRequestOperation of AFNetworking library to initiate request to the web service and handling the parsing logic at the success block.
Each following task is dependent on the successful completion of the previous task. Also, I want the following task to be called after a delay of few seconds after the successful completion of previous. Once task C completes successfully, I'm done.
All of this is happening in the background thread, and hence UI thread is always responsive throughout (my UIActivityIndicator keeps moving throughout for each tasks separately).
Here's the pseudo code snippet:
-(void)viewDidLoad
{
_operationQueue = [[NSOperationQueue alloc]init];
[_operationQueue setMaxConcurrentOperationCount:1];
[self taskA];
}
- taskA
{
NSMutableURLRequest *request = urlA;
AFXMLRequestOperation *operationA = [AFXMLRequestOperation XMLParserRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, NSXMLParser *XMLParser) {
XMLParser.delegate = someClass;
[XMLParser parse];
// Now since the operation is successful, start task B after a delay of 5 seconds
[self performSelector:#selector(taskB) withObject:nil afterDelay:5];
failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, NSXMLParser *XMLParser) {
NSLog(#"NSError: %#",error);
}];
[_operationQueue addOperation: operationA];
}
- taskB
{
NSMutableURLRequest *request = urlB;
AFXMLRequestOperation *operationB = [AFXMLRequestOperation XMLParserRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, NSXMLParser *XMLParser) {
XMLParser.delegate = someOtherClass;
[XMLParser parse];
// Now since the operation is successful, start task C after 10 seconds
[self performSelector:#selector(taskC) withObject:nil afterDelay:10];
failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, NSXMLParser *XMLParser) {
}];
[_operationQueue addOperation: operationB];
[operationB addDependency:operationA]; // This code seems to produce no result and hence seems redundant
}
- taskC
{
NSMutableURLRequest *request = urlB;
AFXMLRequestOperation *operationC = [AFXMLRequestOperation XMLParserRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, NSXMLParser *XMLParser) {
XMLParser.delegate = yetAnotherClass;
[XMLParser parse];
// Now since the operation is successful, mission accomplished!
NSLog(#"Mission accomplished!");
failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error, NSXMLParser *XMLParser) {
}];
[_operationQueue addOperation: operationB];
[operationC addDependency:operationB]; // This code seems to produce no result and hence seems redundant
}
Questions:
I'm able to achieve what I wanted to from the app with this implementation, but I'm not sure if I'm making the right use of NSOperation and NSOperationQueue. Of what I read from Apple docs and tutorials, one of the strengths of NSOperation is using it for dependency establishment between different operations. However, in my example how can I ensure operationB gets executed only after the 'successful' completion of task A and thus leverage the "addDependency" feature of NSOperation?
I also want to ensure that 'taskB' gets called only after a certain
delay after successful completion of 'taskA' and so on. Is [self performSelector:#selector(taskB) withObject:nil afterDelay:5];
the only way to do it? Or are there alternative ways, where I could
use some elements of NSOperation/NSOperationQueues? Or maybe use
something like "dispatch_after"??
Overall, how can I redesign the code better to get the same tasks accomplished using NSOperation?