Accessing XML data online?

Question

I am just testing an app to get data off our web server, previously I had been using:

NSURL, NSURLRequest, NSURLConnection etc. to get the data that I wanted.

But I have just noticed that if I swap to using XML I can simply do the following and pass the results to NSXMLParser:

NSURL *url = [NSURL URLWithString:@"https://www.fuzzygoat.com/turbine?nbytes=1&fmt=xml"];

Am I right in thinking that if your just after XML this is an acceptable method? It just seems strongly short compared to what I was doing before?

gary

Answer 1

That code only creates a URL object that represents a URL. It doesn't make any request or download any data. You still need to use NSURLRequest and NSURLConnection in order to actually download any data from the server.

Also, stay away from methods like 'initWithContentsOfURL:` and friends, unless you understand that they will block the thread that they are called on until complete. For network services, this method shouldn't be used because it'll block your UI for an indeterminate time, because you can't predict how fast the internet connection will be wherever the app is used.

NSURLConnection's asynchronous request system is exactly what you need. It won't block the UI, and provides a nice encapsulated interface to downloading data from a remote location.

Answer 2

Depending on how much XML you get back from the web service, NSXMLParser may not be ideal because the entire XML document has to be read into memory.

Memory is pretty scarce on an iPhone, so using a SAX parser like that in libxml2 is probably better for larger XML files. Instead of reading the entire document into memory, the XML is streamed through and parsed for specific nodes of interest. The memory overhead is lower because less data is stored at once.

Once a node of interest is parsed, an event handler is called to do something useful, like store the node data somewhere.

In this case, take a look at Apple's XMLPerformance sample project for example code.

Answer 3

This is definitely the right way to go. There do exist many different connection methods (including my favorite, ASIHTTPRequest) and many, many different xml parsers (including my favorite, KissXML) that are faster or more memory efficient than the Apple built in methods.

But to answer your question, yes, your logic and design pattern is correct.

UPDATE: Because Jasarien seems to think the question talks about asynchronous actions, I will discuss that here. ASIHTTPRequest handles async very very easily. Just check out the quick samples.