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Oliver Kopp edited this page Jan 7, 2020 · 20 revisions

Please head to https://jabref.readthedocs.io/en/latest/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! It is often convenient to load the FXML file directly from the controller.

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 and in an article focusing on the implementation with JavaFX.

An example

ViewModel:

  • The ViewModel should derive from AbstractViewModel.
public class MyDialogViewModel extends AbstractViewModel {
}
    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!");
}

View - Controller:

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

  • The usual convention is that the controller ends on the suffix *View. Dialogs should derive from BaseDialog.

public class AboutDialogView extends BaseDialog<Void>
  • You get access to nodes in the FXML file by declaring them with the @FXML annotation.
@FXML protected Button helloButton;
@FXML protected ImageView iconImage;
  • Dependencies can easily be injected into the controller using the @Inject annotation.
@Inject private DialogService dialogService;
  • It is convenient to load the FXML-view directly from the controller class. The FXML file is loaded using ViewLoader based on the name of the class passed to view. 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. Note that fields annotated with @FXML or @Inject only become accessible after ViewLoader.load() is called. a View class that loads the FXML file.
private Dependency dependency;

public AboutDialogView(Dependency dependency) {
        this.dependency = dependency;

        this.setTitle(Localization.lang("About JabRef"));

        ViewLoader.view(this)
                  .load()
                  .setAsDialogPane(this);
}
  • Dialogs should use setResultConverter to convert the data entered in the dialog to the desired result. This conversion should be done by the view model and not the controller.
setResultConverter(button -> {
    if (button == ButtonType.OK) {
        return viewModel.getData();
    }
    return null;
});
  • 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.
@FXML
private void initialize() {
    viewModel = new AboutDialogViewModel(dialogService, dependency, ...);

    helloLabel.textProperty().bind(viewModel.helloMessageProperty());
@FXML
private void openJabrefWebsite() {
    viewModel.openJabrefWebsite();
}

View - FXML:

The view consists a FXML file MyDialog.fxml which defines the structure and the layout of the UI. Moreover, the FXML file may be accompanied by a style file that should have the same name as the FXML file but with a css ending, e.g., MyDialog.css. 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.

Resources:

Features missing in JavaFX:

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