Best approach for XML parsing on the iPhone

Question

I've familiarized myself with the NSXMLParser from the iPhone SDK but I find the event-driven nature of it awkward for my purposes. I just want to extract some element values but this concept of having to handle the startElement, foundCharacters, and endElement seems like more work than it really should be. Am I just looking at this the wrong way or is there a simpler tree/DOM-based way of working with XML in the iPhone SDK?

If the advice is to just work with NSXMLParser, are there certain design patterns I can use to keep my code from having 5 levels of nested ifs in the startElement method?

Answer 1

Consider the following code snippet, that uses libxml2, Matt Gallagher's libxml2 wrappers and Ben Copsey's ASIHTTPRequest to parse an XML document.

The nodes instance of type NSArray* will contain NSDictionary* objects that you can parse recursively to get the data you want.

Or, if you know the scheme of your XML document, you can write an XPath query to get you to a nodeContent or nodeAttribute value directly.

ASIHTTPRequest *request = [ASIHTTPRequest alloc] initWithURL:[NSURL URLWithString:@"http://stackoverflow.com/"];
[request start];
NSError *error = [request error];
if (!error) {
    NSData *response = [request responseData];
    NSLog(@"Root node: %@", [[self query:@"//" withResponse:response] description]);
}
else 
    @throw [NSException exceptionWithName:@"kHTTPRequestFailed" reason:@"Request failed!" userInfo:nil];
[request release];

...

- (id) query:(NSString *)xpathQuery withResponse:(NSData *)respData {
    NSArray *nodes = PerformXMLXPathQuery(respData, xpathQuery);
    if (nodes != nil)
        return nodes;
    return nil;
}

Answer 2

Repurposing the code from Seismic XML provides a very good API that creates NSObject subclasses from XML.

If the advice is to just work with NSXMLParser, are there certain design patterns I can use to keep my code from having 5 levels of nested ifs in the startElement method?

I depends on what you are trying to do. You could put your element names in a dictionary and take action based on the relevant object in a dictionary - this is effectively what SeismicXML does.