title: Sorting an array with instances of a custom class
body: <p>I have an array filled with instances of a custom class which contains two String properties, firstname and lastname. Both have a getter method which is equal to the name of the property itself. There is also a method for retrieving the Full name of a person called "getFullName". Consider the example below.</p>
  
  <pre><code> CustomClass *person = [[CustomClass alloc] ...];
   person.firstname  // Returns "Thomas"
   person.lastname // Returns "Meier"
   [person getFullName] // Returns "Thomas Meier"
  </code></pre>
  
  <p>Now I would like to sort this Array by Fullname in a descending Order. I have been looking at some array sorting methods but was not quite able to figure out how to go about this. I guess that I have to create some kind of comparison function which compares two elements, yet how do I tell the SDK which values to pass to this method and where should I place it (in the custom class or in the class where the sorting happens?). Maybe there is another/better way of going about this? Admittedly I have close to none experience with sorting arrays.</p>
  
  <p>Thanks a lot for your help!</p>
  
  <p>Ps. The code should run on iOS 3.2</p>