Code JavaFX

Architecture: Model - View - (Controller) - ViewModel (MV(C)VM)

The goal of the MVVM architecture is to separate the state/behavior from the appearance of the ui. This is archived by dividing JabRef into different layers, each having a clear responsibility.

• The Model contains the business logic and data structures. These aspects are again encapsulated in the logic and model package, respectively.
• The View controls the appearance and structure of the UI. It is usually defined in a FXML file.
• View model converts the data from logic and model in a form that is easily usable in the gui. Thus it controls the state of the View. Moreover, the ViewModel contains all the logic needed to change the current state of the UI or perform an action. These actions are usually passed down to the logic package, after some data validation. The important aspect is that the ViewModel contains all the ui-related logic but does not have direct access to the controls defined in the View. Hence, the ViewModel can easily be tested by unit tests.
• The Controller initializes the view model and binds it to the view. In an ideal world all the binding would already be done directly in the FXML. But JavaFX's binding expressions are not yet powerful enough to accomplish this. It is important to keep in mind that the Controller should be as minimalistic as possible. Especially one should resist the temptation to validate inputs in the controller. The ViewModel should handle data validation!

The only class which access model and logic classes is the ViewModel. Controller and View have only access the ViewModel and never the backend. The ViewModel does not know the Controller or View.

More details about the MVVM pattern can be found in an article by Microsoft.

An example

ViewModel:

• The ViewModel should derive from AbstractViewModel.

public class MyDialogViewModel extends AbstractViewModel {
}

• Add a (readonly) property as a private field and generate the getters according to the JavaFX bean conventions:

    private final ReadOnlyStringWrapper heading = new ReadOnlyStringWrapper();

    public ReadOnlyStringProperty headingProperty() {
        return heading.getReadOnlyProperty();
    }

    public String getHeading() {
        return heading.get();
    }

• Create constructor which initializes the fields to their default values. Write tests to ensure that everything works as expected!

public MyDialogViewModel(Dependency dependency) {
    this.dependency = Objects.requireNonNull(dependency);
    heading.set("Hello " + dependency.getUserName());
}

• Add methods which allow interaction. Again, don't forget to write tests!

public void shutdown() {
    heading.set("Goodbye!");
}

Controller:

• The "code-behind" part of the view, which binds the View to the ViewModel.

public class AboutDialogController extends AbstractController<AboutDialogViewModel>

@FXML protected Button helloButton;
@FXML protected ImageView iconImage;

• Dependencies can easily be injected into the controller using the @Inject annotation.

@Inject private DialogService dialogService;

@FXML
private void initialize() {
    viewModel = new AboutDialogViewModel(dialogService, clipBoardManager, buildInfo);
}

• The initialize method may use data-binding to connect the ui-controls and the ViewModel. However, it is recommended to do as much binding as possible directly in the FXML-file.

    helloLabel.textProperty().bind(viewModel.helloMessageProperty());

@FXML
private void openJabrefWebsite() {
    viewModel.openJabrefWebsite();
}

• The current stage can be received using getStage(), which is helpful to close the current dialog getStage().close().

View:

The view consists of two parts:

• a FXML file "MyDialog.fxml" which defines the structure and the layout of the UI. It is recommended to use a graphical design tools like SceneBuilder to edit the FXML file. The tool Scenic View is very helpful in debugging styling issues.

• a View class that loads the FXML file. The fxml file is loaded automatically using the same name as the class. To make this convention-over-configuration approach work, both the FXML file and the View class should have the same name and should be located in the same package.

• For dialogs, we simply derive from AbstractDialogView and implement the show method.

public class MyDialogView extends AbstractDialogView {

    @Override
    public void show() {
        FXDialog myDialog = new FXDialog(AlertType.INFORMATION, Localization.lang("My first dialog"));
        myDialog.setDialogPane((DialogPane) this.getView());
        myDialog.show();
    }
}

Resources:

• curated list of awesome JavaFX frameworks, libraries, books and etc...
• ControlsFX amazing collection of controls
• usage of icon fonts with JavaFX
• Undo manager
• Docking manager or
• additional bindings or EasyBind
• Validation framework
• mvvm framework
• CSS Reference

Features missing in JavaFX:

• bidirectional binding in FXML, see official feature request