Question

I have created an application, using ARC, that parses data from an online XML file. I am able to get everything I need using one class and one call to the API. The API provides the XML data. Due to the large xml file, I have a lot of variables, IBOutlets, and IBActions associated with this class.

But there are two approaches to this:

1) create a class which parses the XML data and also implements that data for your application
, i.e. create one class that does everything (as I have already done)

or

2) create a class which parses the XML data and create other classes which handle the data obtained from the XML parser class, i.e. one class does the parsing and another class implements that data

Note that some APIs that provide XML data track the number of calls/minute or calls/day to their service. So you would not want several classes calling the API, it would be better to make one request to the API which receives all the data you need.

So is it better to use several smaller classes to handle the xml data or is it fine to just use one large class to do everything?

Answer 1

When in doubt, smaller classes are better.

2) create a class which parses the XML data and create other classes which handle the data obtained from the XML parser class, i.e. one class does the parsing and another class implements that data

One key advantage of this is that the thing that the latter class models is separate from the parsing work that the former class does. This becomes important:

• As Peter Willsey said, when your XML parser changes. For example, if you switch from stream-based to document-based parsing, or vice versa, or if you switch from one parsing library to another.
• When your XML input changes. If you want to add support for a new format or a new version of a format, or kill off support for an obsolete format, you can simply add/remove parsing classes; the model class can remain unchanged (or receive only small and obvious improvements to support new functionality in new/improved formats).
• When you add support for non-XML inputs. For example, JSON, plists, keyed archives, or custom proprietary formats. Again, you can simply add/remove parsing classes; the model class need not change much, if at all.

Even if none of these things ever happen, they’re still better separated than mashed together. Parsing input and modeling the user’s data are two different jobs; mashing them together makes them hard or impossible to reason about separately. Keep them separate, and you can change one without having to step around the other.