Question

I have a question about GUI design, specifically with Java Swing and creating clean separation between presentation and model.

It’s a bit difficult to describe, but essentially we have lots of reference data in our system (i.e. that would correspond to lookup tables in the DB). We want people to be able to edit them all from one screen.

So, in an ideal world what we’d like is a combo box in the top-left corner with a list of ‘types’ of reference data (so each corresponding to one table in the DB).

Then, when selected, a list of the data is populated below, also a filter (or search box). When one of these items is selected, the panel to the right is activated which will allow the actual data to be edited.

Now, here’s the problem: each type of data we need to edit is different, so it has different fields etc. We could go with a generic solution but I’m not really a fan of them – there are lots of different validation rules for each etc, even for different clients, and it would be a nightmare to manage.

We’re using the Presentation Model pattern to achieve some degree of separation between GUI code and the model but I can’t think of a clean way of doing this which doesn’t somehow blur the line of responsibilities a bit.

What are the ways you have solved problems like this?

[Note: apologies for the long question, hope it’s understandable, I can re-phrase if necessary]

Answer 1

You could use the Factory Pattern to create a UI widget for the element that you are selecting. You could also use it to create a validation rule object depending on the type. This would give you some of the flexibility you desire.

So you can have something like:

IWidget widget = UIFactory.createFor(myObject.getType())

That can be invoked on the selection event to create the right widget to edit the selected element.

The IWidget could have methods such as:

validateData()
refreshData()
setDataElement(IDataElement element)

That would allow you to treat all UI widgets generically, but still have a special UI widget for each element type. I am assuming that the elements that you are selecting from the table all implement some IDataElement interface that contains the getType() method.

I used this solution tied together with the Eclipse Extension mechanism to plug-in new UI elements into my “base” solution, to have an extensible core and a high level of reuse. You could achieve something similar by injecting types and widgets into your factory, either manually or with Spring.