Using FXForm2 with EMF Models

Based on these considerations from July, we gave FXForm2 a shot for generating forms from EMF models. It worked quite smoothly after we wrote the factories that defined how the custom data types used in our models should be displayed.

We found a few things that are worth noting:

  1. Using Java Bean Validation
    In order to validate our EMF models using the Java Bean Validation API (JSR-303) that comes with FXForm2, we wrote wrapper classes for those model elements that we wanted to add constraints to. We decided to not touch the generated code.
  2. Using another validation implementationFXForm2 can use any implementation of JSR-303. Using the Hibernate implementation is suggested on the FXForm2 website, but we found it easy to supply our own implementation based on EMF’s validation features such as the Diagnostician class.
  3. Validation philosophies
    When you enter an invalid value into a field, FXForm2 won’t update the corresponding model attribute. The value you see in the form differs from the value in the model. The model thus always has a valid state.EMF validation typically works in a different way: you start the validation operation only after all model values were set. This allows for invalid states of the model.
  4. Dynamic beans
    An open issue
    seems to be (as least for us) the handling of a String-to-String Map attribute inside an EMF bean class that stores user-supplied key-value pairs which should be displayed as regular attributes of the bean. Antoine suggested a solution based on a custom control (with a factory and a skin), but it comes with a different visual appearance for the user-defined attributes. This is work in progress.

GUI Generation with JavaFX

Recently, we have had a look at JavaFX libraries for generating UIs in a dynamic way. The idea is that we have a data model (a JavaBean class, an EMF model class, a model class with JavaFX properties,…) as input for some GUI builder that takes the model and generates a matching user interface with bindings between the model and the JavaFX controls. In a perfect world, this library would allow us to use a variety of data models and to customise the generated user interface.

We have had three candidates (all open source). As we use EMF a lot, two of them are based on EMF models.

1. FXForm2

This pops up early when you are looking for UI generation libraries for JavaFX. As the name implies, it is meant for generating forms from model beans.

A sample form generated by FXForm2

The main features include:

  • Automatic form generation and binding to bean properties
  • CSS support
  • Bean Validation handling (JSR 303)
  • Fields reordering and filtering
  • Tooltips
  • Localization

It takes three lines to add a generated form to your JavaFX scene graph:

2. EMF Edit for JavaFX

This library has a broader scope than FXForm2 as it can generate an entire RCP application with a sophisticated visual model editor rather than just a couple of form fields. Or you can define your own controls and easily bind your EMF model instances to these controls, including support for drag & drop and undo/redo commands. An example of a user interface based on a “Contacts” model can be seen in Tom’s video from the link above.

A sample application using EMF Edit for JavaFX

3. EMF Client Platform

This takes the idea of EMF Edit one step further. As the ECP website says:

The goal is to provide a one-click application based on a given EMF model. Besides the EMF model, no additional components have to be developed or generated.

A sample application as generated by the EMF Client Platform

So when you have your EMF model, you are only one click away from a complete client application with a model explorer, an editor, a persistence mechanism, and a couple of other nice things. The editor for the model attributes is similar to the data form generated by FXForm2, but it is embedded in an entire application whose pieces are customisable and extensible.

The bad news is that there is currently no JavaFX support for ECP.
As Tom Schindl has pointed out in the comments section, there is a first version of JavaFX support for ECP in one of the development branches of the e(fx)clipse project. See here.

4. Summary

We have not found the perfect solution yet. FXForm2 has a promising approach for easily generating forms, of which we are going to have a lot in our final product. It requires some tweaks to make it work with EMF models but that is a small obstacle. What worries me a bit is the maturity of this library: the latest version is 0.2.2. So is it ready for production use? Well, there’s at least one real-world application that uses it.

EMF Edit is a very powerful framework but does not generate controls on the granularity we require for most parts of our application. It will certainly be of use for fancy features like drag & drop and the command stack. Maybe we can combine its strengths with the power of FXForm2 for generating really rich forms.

The EMF Client platform has a very appealing one-click approach but it lacks support for JavaFX. Once this limitation is gone, we may give it another look. A major question will then be how far we can customise the basic layout of the generated application which by default is very different from what we have in mind for our user interface.


Dear tree huggers,

I’m one of you. I like trees – preferably on the left of my application. They give me the impression that I exactly know where I am and where I can go next. Just recently I learnt how much I appreciate a tree as a navigation element when I worked with Confluence 5 for the first time and tried to replace the navigation tree on the left by the new space sidebar. It felt strange to me because I always looked for things that were not there. I tried to familiarise myself with the dynamic contents of the sidebar, but I gave up after a couple of days. The mental overload was too high.

Why was it so difficult to get rid of the tree?

  • As a developer I’m used to thinking about tree-structured data so trees are in my head all the time..
  • I encounter trees in many of my tools: my IDE, my file manager, my email client.

So I live in a forest. As this is my natural habitat, I’m pretty good with trees. I know how they work and how to find what I want as they are an accurate representation of my mental model in most cases. In other words: my brain was not ready for that sidebar thing.

But there are other people in the world. People who tend to think in different ways than a software developer. Scary, I know.
Some of these people use the software I build and at the same time do not like trees, in particular as navigational elements. Their mental model is different from mine, maybe workflow-centric rather than data-centric. They might not think of the data they’re working with in the same way I do. It’s not unlikely that some of them do not think about their data at all but simply execute a given (no-brainer) task.

In these use cases, a tree is of limited value at best and can even be harmful when the user is faced with too many options and too many paths that do not get him where he wants to go. It is better to restrict user choices and thereby make the user focus on the current task. A context-sensitive UI helps guide the user through the given workflow whereas a tree might encourage the user to meander through the application and explore things are are not to be explored.

No wonder a full chapter of Designing Interfaces is about navigation. No wonder the first paragraph in Microsoft’s developer documentation on tree views is titled “Is this the right control?” No wonder even a small thing like a breadcrumb bar deserves a full-blown description on patternry. Because even with a limited set of navigational widgets, you have many options to do it right and many more to do it wrong. There’s more to navigation than just putting an extra menu bar somewhere. Or worse: a tree.

Having written this already helps me to let go of the tree. Now it’s time to look for alternatives. In my JavaFX world this means goodbye TreeView and hello …

I’ll save the answer for another blog post. Stay tuned.