How to read in and parse an XML file on the iphone?

Question

I have a web server which returns an XML file. Lets say http://www.foo.bar/foo.php?wantXML=1

How would I fetch that file from the server and then parse it to access the data? I guess I would have to spawn a new thread and do the whole thing in the background to not block the UI? What classes must I look at?

Answer 1

You can attempt to do:

• String manipulations
• XPATH

Id opt for xpath in all but the most simple cases - and even in those, you can't argue against xpath. Im not sure of the libraries though, but I know libXML is written in C and supported on the iphone.

For string manipulations, you can use the NS* family of methods.(substringFromIndex, substringToIndex, etc) And don't forget: http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Classes/NSXMLParser_Class/Reference/Reference.html

Big Nerd Ranch, 'Parsing XML in Cocoa': http://weblog.bignerdranch.com/?p=48

Answer 2

I've used two approaches: NSXMLParser for simple and small files, and libxml for larger files. But there are libraries such as TouchXML that can simplify the process as well.

Basically, if you have a small data set, in memory DOM processing can work fine. But in a device such as the iPhone, you're better off using SAX-based parsers such as libxml2.

When you need to load the data:

[self performSelectorInBackground:@selector(LoadYourData) withObject:nil];

will not block the main UI thread.

For libxml2, you will need to implement C callbacks to process the chunks of data coming in from a NSURLConnection.

Answer 3

To pull down XML or other stuff over http I recommend looking into using ASIHTTPRequest

Feel free to have a look at my convenient classes I created to parse simple XML documents like you can get from Nike+. Link

Basically the usage is as follows

NameValueParser *parser = [NameValueParser parser];
[parser addFieldName:@"screenName"]; // Name
[parser addFieldName:@"rank"];       // Position
[parser addFieldName:@"progress"];   // Distance
[parser parseData:data];

NSLog(@"%@", [parser list]); // Lets see what we got

Answer 4

SeismicXML sample from Apple is exaclty what you are looking for.