Model-View-Presenter

About 3 min

Intent

MVP aims to separate the user interface (UI) logic from the business logic and model in a software application, enabling easier testing and maintenance.

Explanation

Real-world example

Consider a real-world analogy of the Model-View-Presenter (MVP) pattern using a restaurant scenario:
Model: This is the kitchen in a restaurant, where all the cooking and preparation of dishes happens. It's responsible for managing the food ingredients, cooking processes, and ensuring that recipes are followed correctly.
View: This represents the dining area and the menu presented to the customers. It displays the available dishes, takes orders, and shows the final presentation of the food. However, it doesn't decide what's cooked or how it's prepared.
Presenter: Acting as the waiter, the presenter takes the customer's order (input) and communicates it to the kitchen (model). The waiter then brings the prepared food (output) back to the customer in the dining area (view). The waiter ensures that what the customer sees (the menu and food presentation) aligns with what the kitchen can provide, and also updates the view based on the kitchen's capabilities (e.g., out-of-stock items).
In this analogy, the clear separation of roles allows the restaurant to operate efficiently: the kitchen focuses on food preparation, the dining area on customer interaction, and the waiter bridges the two, ensuring smooth operation and customer satisfaction.

In plain words

The Model-View-Presenter (MVP) pattern separates the user interface, business logic, and data interaction in an application, with the presenter mediating between the view and the model to facilitate clear communication and updates.

Wikipedia says

Model–view–presenter (MVP) is a derivation of the model–view–controller (MVC) architectural pattern, and is used mostly for building user interfaces. In MVP, the presenter assumes the functionality of the "middle-man". In MVP, all presentation logic is pushed to the presenter.

Programmatic example

The Model-View-Presenter (MVP) design pattern is a derivative of the well-known Model-View-Controller (MVC) pattern. It aims to separate the application's logic (Model), GUIs (View), and the way that the user's actions update the application's logic (Presenter). This separation of concerns makes the application easier to manage, extend, and test.

Let's break down the MVP pattern using the provided code:

Model: The Model represents the application's logic. In our case, the FileLoader class is the Model. It's responsible for handling the file loading process.

@Getter
public class FileLoader implements Serializable {
  //...
  public void setFileName(String fileName) {
    this.fileName = fileName;
  }
  
  public boolean fileExists() {
    //...
  }

  public String loadData() {
    //...
  }
}

View: The View is responsible for displaying the data provided by the Model. Here, the FileSelectorView interface and its implementation FileSelectorJFrame represent the View. They define how to display data and messages to the user.

public interface FileSelectorView {
  //...
  void setPresenter(FileSelectorPresenter presenter);
  void open();
  void close();
  void showMessage(String message);
  void displayData(String data);
  String getFileName();
}

public class FileSelectorJFrame implements FileSelectorView {
  //...
  @Override
  public void displayData(String data) {
    this.dataDisplayed = true;
  }
}

Presenter: The Presenter acts as a bridge between the Model and the View. It reacts to the user's actions and updates the View accordingly. In our example, the FileSelectorPresenter class is the Presenter.

public class FileSelectorPresenter implements Serializable {
  //...
  public void setLoader(FileLoader loader) {
    this.loader = loader;
  }

  public void start() {
    view.setPresenter(this);
    view.open();
  }

  public void fileNameChanged() {
    loader.setFileName(view.getFileName());
  }

  public void confirmed() {
    //...
  }

  public void cancelled() {
    view.close();
  }
}

Finally, we wire up the Presenter, the View, and the Model in the App class:

public class App {
  public static void main(String[] args) {
    var loader = new FileLoader();
    var frame = new FileSelectorJFrame();
    var presenter = new FileSelectorPresenter(frame);
    presenter.setLoader(loader);
    presenter.start();
  }
}

In this setup, the App class creates instances of the Model, View, and Presenter. It then connects these instances, forming the MVP triad. The Presenter is given a reference to the View, and the Model is set on the Presenter. Finally, the Presenter is started, which in turn opens the View.

Applicability

Use MVP in applications where a clear separation of concernsopen in new window is needed between the presentation layer and the underlying business logic. It's particularly useful in client-server applications and enterprise-level applications.

Known Uses

Desktop applications like those built using Java Swing or JavaFX.
Web applications with complex user interfaces and business logic.

Consequences

Benefits:

Enhances testability of UI logic by allowing the presenter to be tested separately from the view.
Promotes a clean separation of concerns, making the application easier to manage and extend.
Facilitates easier UI updates without affecting the business logic.

Trade-offs:

Increases complexity with more classes and interfaces.
Requires careful design to avoid over-coupling between the presenter and the view.

Model-View-Controller (MVC)open in new window: MVP is often considered a variant of MVC where the presenter takes over the controller's role in managing user input and updating the model.
Model-View-ViewModel (MVVM)open in new window: Similar to MVP but adapted for frameworks like WPF or frameworks that support data binding, making the view update automatically when the model changes.