Making an Asynchronous Cocoa class work in a synchronous manner - objective-c

Question

So I'm writing a function that authenticates against an API that returns an XML document packed with things I'd like to pass. The function can make a synchronous call with NSURLConnection's sendSynchronousRequest method, quite easily. Yet, once this method returns, I need to instantiate an instance of NSXMLParser, initiate it with the data, let it parse, etc, etc.
What I'd like to do, is in my function (after sendSynchronousRequest returns), instantiate NSXMLParser, give it the data to parse, and in a single method call, get it to start the parse, and not return until the parse is over.
For example:
- (void) myFunction
{
/* other code */
NSData *returnedData = [NSURLConnection sendSynchronousRequest:authRequest returningResponse:&authResponse error:&authError];
MyParserClass *parser = [[MyParserClass alloc] initWithData:returnedData];
[parser parseData];
}
In the above example, MyParserClass is a NSXMLParser delegate, and does all the parsing in the usual, delegated fashion. parseData will start the parse, and not return until it is over.
In what manner should I write parseData? A block-approach?
EDIT: I just remembered the -parse function in NSXMLParser is synchronous. Still, i'd love to know if anyone could explain a way to do this in asynchronous classes of any sort.

Answer 1

I'd recommend writing a class that implements the NSXMLParserDelegate protocol (for example, MyParserDelegate). When the delegate methods get called by the parser, it should build up a data structure with the information you want to extract from the XML file. I'd call it as follows:
// create the delegate
MyParserDelegate *delegate = [[MyParserDelegate alloc] init];
// create the parser
NSXMLParser *parser = [[NSXMLParser alloc] initWithData:returnedData];
[parser setDelegate:delegate];
// parse the file
if ([parser parse])
{
// the XML was valid and parsed without error
// now, do something with the data you extracted
// e.g., self.xmlData = [delegate xmlBasedDataStructureBuiltByDelegate];
}
else
{
// the XML was invalid
// handle the error
}
The functionality of MyParserDelegate depends entirely on what you want to extract out of the XML file. I'd recommend reading Apple's Event-Driven XML Programming Guide for more information.
Remember, if you want to use a synchronous NSURLConnection, you should do this on a background thread.