Presentation Model

About 3 min

Intent

To separate the logic of the user interface (UI) from the business logic by creating a model that represents the data and behavior of the UI independently.

Explanation

Real world example

An analogous real-world example of the Presentation Model design pattern is the relationship between a scriptwriter, an actor, and a director in a theater production. The scriptwriter creates the script (analogous to the business logic), which the actor then interprets and performs on stage (analogous to the user interface). The director acts as the intermediary, ensuring that the actor's performance aligns with the script and the vision of the play (similar to the Presentation Model coordinating the UI and the business logic). This separation allows the script to be rewritten without changing the actor's techniques or the director's interpretation, ensuring flexibility and maintainability.

In plain words

The Presentation Model design pattern separates the UI logic from the business logic by creating an intermediate model that represents the data and behavior of the UI independently, enhancing testability, maintainability, and flexibility.

Programmatic example

The Presentation Model design pattern is a pattern that separates the responsibility of managing the state and behavior of the GUI in a separate model class. This model class is not tied to the view and can be used to test the GUI behavior independently from the GUI itself.

Let's take a look at the code provided and see how it implements the Presentation Model pattern.

First, we have the Album class. This class represents the data model in our application. It contains properties like title, artist, isClassical, and composer.

public class Album {
    private String title;
    private String artist;
    private boolean isClassical;
    private String composer;

    public Album(String title, String artist, boolean isClassical, String composer) {
        this.title = title;
        this.artist = artist;
        this.isClassical = isClassical;
        this.composer = composer;
    }

    // getters and setters...
}

Next, we have the DisplayedAlbums class. This class is responsible for managing a collection of Album objects.

public class DisplayedAlbums {
    private List<Album> albums;

    public DisplayedAlbums() {
        this.albums = new ArrayList<>();
    }

    public void addAlbum(String title, String artist, boolean isClassical, String composer) {
        if (isClassical) {
            this.albums.add(new Album(title, artist, true, composer));
        } else {
            this.albums.add(new Album(title, artist, false, ""));
        }
    }

    // other methods...
}

The PresentationModel class is where the Presentation Model pattern is implemented. This class is responsible for managing the state and behavior of the GUI. It contains a reference to the DisplayedAlbums object and provides methods for interacting with the selected album.

public class PresentationModel {
    private final DisplayedAlbums data;

    private int selectedAlbumNumber;
    private Album selectedAlbum;

    public PresentationModel(final DisplayedAlbums dataOfAlbums) {
        this.data = dataOfAlbums;
        this.selectedAlbumNumber = 1;
        this.selectedAlbum = this.data.getAlbums().get(0);
    }

    // other methods...
}

The App class is the entry point of the application. It creates a View object and calls its createView method to start the GUI.

public final class App {
    public static void main(final String[] args) {
        var view = new View();
        view.createView();
    }
}

In this example, the PresentationModel class is the Presentation Model. It separates the GUI's state and behavior from the View class, allowing the GUI to be tested independently from the actual GUI components.

Class diagram

Applicability

Use the Presentation Model Pattern when

Use when you want to decouple the UI from the underlying business logic to allow for easier testing, maintenance, and the ability to support multiple views or platforms.
Ideal for applications where the UI changes frequently or needs to be different across various platforms while keeping the core logic intact.

Known Uses

JavaFX applications: Utilizing JavaFX properties and bindings to create a clear separation between the UI and business logic.
Swing applications: Employing a Presentation Model to decouple Swing components from the application logic, enhancing testability and flexibility.
Android apps: Implementing MVVM architecture using ViewModel classes to manage UI-related data and lifecycle-aware components.

Consequences

Benefits:

Decoupling: Enhances separation of concernsopen in new window, making the system more modular and testable.
Testability: Facilitates unit testing of UI logic without the need for actual UI components.
Maintainability: Simplifies maintenance by isolating changes to the UI or business logic.
Flexibility: Supports multiple views for the same model, making it easier to adapt the UI for different platforms.

Trade-offs:

Complexity: Can introduce additional layers and complexity in the application architecture.
Learning Curve: May require a deeper understanding of binding mechanisms and state management.

Model-View-Controller (MVC)open in new window: Similar in that it separates concerns, but Presentation Model encapsulates more of the view logic.
Model-View-Presenter (MVP)open in new window: Another UI pattern focusing on separation of concerns, but with a different interaction model.
Observeropen in new window: Often used within the Presentation Model to update the UI when the model changes.