Supervising Presenter

The Supervising Presenter pattern addresses the challenge of separating application logic from the user interface in a way that allows for testability and maintainability. It achieves this by introducing a Presenter that mediates between the Application (containing business logic) and the View (UI). The Presenter receives user input from the View, instructs the Model to perform actions, and then formats the Model’s output for display in the View. Crucially, the Presenter doesn’t directly manipulate the View; it provides data and instructions, and the View is responsible for rendering them.

This pattern is particularly useful in applications with complex UI logic or where the UI might be swapped out (e.g., web, mobile, desktop). It promotes a clear separation of concerns, making it easier to test the application logic independently of the UI and to evolve the UI without impacting the core behavior. This is a variation of the traditional MVP (Model-View-Presenter) pattern, emphasizing the Presenter’s role in coordinating and supervising the view’s updates.

Usage

The Supervising Presenter pattern is commonly used in:

• Web Applications (especially Single Page Applications - SPAs): Frameworks like React, Angular, and Vue.js often utilize variations of this pattern. The “controller” or component receives user events (input), interacts with services (the Model), and then provides data for the view to render.
• Desktop Applications: When building desktop applications with UI frameworks like Qt or WPF, this pattern helps isolate the UI from the application’s core logic.
• Mobile Applications: Similar to web applications, mobile apps benefit from the separation of concerns, especially when dealing with asynchronous data loading and complex UI interactions.
• Test-Driven Development (TDD): The clear separation of concerns makes it easier to write unit tests for the application logic without needing to mock or interact with the UI.

Examples

1. AngularJS/Angular: In Angular, components often act as Presenters. They receive user input through event bindings, call services (representing the Model), and then update the view by assigning data to component properties. The view is defined in the component’s template and automatically reflects these changes. Angular’s data binding effectively represents the supervised updates by the presenter.

2. ASP.NET MVC/Razor Pages: While ASP.NET MVC doesn’t strictly enforce an MVP pattern, the Controller often functions as the Presenter. It handles user requests, interacts with data models (the Model), and then passes data to the View (Razor Page) for rendering. ViewModels are frequently used to format the data specifically for the View, further embodying the Presenter’s role.