2007-10-27 Thinking about wizards

In the previous post, I talked about how I was coding up a wizard-type bunch of screens, and was using the MVC pattern here as implemented by PEARs HTML_QuickForm_Controller class. Each screen basically has three actions: 'display screen', 'previous screen' and 'next screen'. The last screen has the action 'finish'.

You have to be careful with this approach; the number of actions probably isn't limited to these at all. Consider the following example:

1. In screen 1, the user must make a choice: do you want apples or bananas? User chooses apples.
   
2. In screen 2, the number of apples is calculated and displayed. This took 20 seconds. Then the user chooses the percentage of the apples.
   
3. In screen 3, the user must choose how the delivery is made.

Suppose the user goes back from three to two. The 'display' action is called and, using the choice from the first screen, the number of apples is recalculated. But that's not what the user wants; he just wishes to change the percentage of apples.

So what we need is an action that's derived from 'next', let's call it 'calculate'. This action then checks whether there was a previous choice, whether this differs from the current choice and if so, does a new calculation. The result is saved in the session. We then do whatever 'next' normally does.