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GMF: Beyond the Wizards

by Jeff Richley

In today's development environment, users expect to be able to visualize data, configuration, and even the processes of a system. For this reason, they use tools to communicate requirements visually with stakeholders and subject matter experts. Think for a moment about UML, it takes a very complex set of data and represents it visually to simplify the communication of software requirements and design. Likewise, there are potential visual tools for describing workflows, data mining, server management, and many other business processes. These tools are able to boost productivity and reduce cost, which is obviously a win-win situation.

Historically, writing these tools has been very time consuming and reserved for those GUI gurus that are well above mere mortals. However, that barrier has been broken down for us by the folks working on the Eclipse Graphical Modeling Framework (GMF).

You may be wondering, "What is GMF and what can it do for me?" GMF is a framework that takes a set of configuration files (a domain model, a graphical definition, and a tool definition), puts them all in a blender, and **poof - magic** out comes a professional looking Eclipse plug-in. Not only does it generate most of the functionality that you have designed, it also gives many freebies such as printing, drag-and-drop, save to image, and customization. Once you have completed the plug-in and all of its handy features, you can then distribute it to your user base for widespread use. There are even features of the Eclipse Plug-in Development Environment (PDE) for creating a distribution site that will help with the nightmare of keeping all of those clients up-to-date.

If you've done any UI programming at all, you realize just how much feature (read: bug) prone coding this eliminates. All of the MVC setup, layout management, property listeners, and the like are generated for you. The mundane, cookie cutter work is generated, which allows you to concentrate on the fun and creative part of your projects.

Tutorials that show you how to get started with GMF jump right into the wizards that are provided as part of the SDK. The wizards and dashboard that are used to develop GMF applications are very powerful. With the exception of your data model, all of the configuration files can be generated from wizards. I am all for wizards, but I tend to go by the motto "Don't generate what you don't understand." Let's take a look under the covers of the wizards, in particular, ecore, gmfgraph, gmftool, and gmfmap.

The domain model, ecore/genmodel files, is the starting place for development of most Eclipse-based applications. The basic development pattern for EMF is to model your domain objects and have EMF generate your entire model code base, including beans and glue code. EMF is not discussed in depth in this article, but resources are listed at the end.

The graphical and tooling definitions are straightforward. The graphical side is a list of figures, described in gmfgraph files, which will be used in the diagram to display classes from the domain model. The gmftool file is a tooling definition that defines what text you want to display on the tool palette and the button's tool tip.

The final step is to tell GMF how all of these pieces work together by creating a gmfmap file. This is the glue that brings the other three configuration files together by telling GMF what action to take when a tool is selected, what classes are to be created, and what figures to render when those classes are added to the diagram. Once everything is wired together, generate a gmfgen file and application code, fire up a test instance of Eclipse, and test out your new application.

Now that we have talked about what GMF applications are and have a general idea of the steps involved in making them, let's take a look at a sample application that models managing a coffee shop. The beginning functionality allows you to add managers and employees, as well as associate a manager to the employees that she is responsible for. This is a fairly handy little tool, but it would be even better if we could add coffee machines to the shop. After all, this is a coffee shop and we need to make hot dirty brown water, right?

Let's fire up Eclipse to see the original plug-in and then we will add a coffee machine into the mix. Once you have added the projects to Eclipse, run the sample application (see Figure 1).

Image showing how to run a new eclipse process
Figure 1. Running an Eclipse plug-in

Create a new coffee shop diagram by selecting File->New->Other->Examples->Coffee Diagram. This will give you a brand new diagram to play around with (Figure 2). Go ahead, add a manager or two, a few employees, and wire the managers with their employees. Once you have created a diagram, save it — in fact, keep it for later when you have wired in the coffee machines.

Image of the orignal version in action
Figure 2. Sample coffee shop diagram

Now that you have the original set up and working, let's add the ability to create instances of the CoffeeMachine class. The steps for adding a creation action will be:

  • Define the figure for display
  • Define the creation tool for the tool palette
  • Map the creation tool, display figure, and the backing model class

Defining the Figure for Display

Let's first look at creating figures for displaying the CoffeeMachine for your store. Open the coffee.gmfgraph file and poke around to see what is inside (Figure 3). There are four main types of elements in the hierarchy that you need to understand:

  • Figure Gallery: Shapes for the application
  • Nodes: Graphical representations of the domain model
  • Diagram Labels: Labels for the Nodes that give helpful feedback to the user
  • Connections: Lines denoting relationships between graphical elements

Image of the coffee.gmfgraph file
Figure 3. View of the coffee.gmfgraph file

The first step in defining the diagram is to create a figure for the editor to use. Right-click on the Figure Gallery and select New Child->Rectangle (or any other shape that suits your fancy). Select the newly created Rectangle and look at the Properties view. The one line item that must be filled in, at this point, is the Name field. Let me give you a sage word of advice when it comes to naming elements: "Make sure you name your elements so that they are easily identifiable." One mistake that I made was to have vague names that looked very similar to other elements. You will be very happy in the mapping phase if you stay consistent. One naming convention that I typically use is <NameOfModelClass>Figure or <NameOfModelClass>Diagram. Pick a method that works for you, but once picked, stick with it.

For a good user experience, we would like a figure label to tell what type of model is being displayed. To add a label that shows that the rectangle is actually a coffee machine, right-click on the CoffeeMachineFigure that you just created and select New Child»Label. In the Properties view, give the new Label a name; sticking with the naming convention, it would be something like CoffeeMachineFigureLabel. The Text field denotes what will be displayed on the figure label when it is drawn in the editor. Enter a phrase that would help your user know that it is a coffee machine, such as "<- Coffee Machine ->". Once again, pick a standard way of denoting figures and stick with it; this will go a long way for your users.

In order for GMF to display a model's representation in a diagram, there needs to be a Node to map it to. Create a Node by right-clicking the Canvas and selecting New Child->Nodes Node. This configuration is very straightforward; give it a name and select the figure you want it to use when displaying.

The next step is to make a Diagram Label node. This element will add text to a diagram figure for user feedback. Right-click on the Canvas and select New Child->Labels->Diagram Labels. There are two properties to complete here: Name and Figure. Sticking with our naming conventions, name the new Diagram Label CoffeeMachineDiagramLabel. The Figure is the element from the Figure Gallery to use for display. Select the CoffeeMachineFigureLabel from the drop down list.

There you have it, a finished gmfgraph definition file for adding a CoffeeMachine to a diagram.

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