Model-View-Controller (MVC) Pattern Explained

Posted on Apr 29, 2025 in Computers

Understanding the MVC Pattern

Model-View-Controller (MVC) is a software architectural style that separates application data, user interface (UI), and control logic into three distinct components. The MVC pattern is frequently used in web applications, where the View is often the HTML page and associated code rendering dynamic data, the Model encompasses the data management system (like a database) and business logic, and the Controller handles user input events received from the View.

Component Descriptions

Model

This component represents the specific information the system operates on. Essentially, the Model manages the application’s data and business rules. It should ideally remain independent of the View and Controller, focusing solely on the data state and logic. While it provides data, it doesn’t dictate how that data is presented.

View

This component displays the Model’s data in a format suitable for user interaction, typically the user interface. It renders the data provided by the Model and forwards user input (like clicks or form submissions) to the Controller.

Controller

This component responds to events, usually user actions initiated through the View. It processes these events, interacts with the Model (e.g., querying or updating data), and selects the appropriate View to display the results.

Many systems utilize a database management system, which broadly aligns with the Model component of MVC. While related to layered architectures, MVC specifically aims to separate the presentation layer (View and parts of the Controller handling UI logic) from the data access and business logic (Model and parts of the Controller handling business rules). This separation facilitates parallel development and maintenance, as the UI (View) and interaction logic (Controller) often have different lifecycles than the underlying data model.

Typical Control Flow

Although different MVC implementations exist, the control flow generally proceeds as follows:

  1. The user interacts with the user interface (e.g., clicks a button or link).
  2. The Controller receives notification of the user’s action from the View object. The Controller handles the incoming event, often via an event handler or callback function.
  3. The Controller accesses the Model, potentially updating it based on the user’s action (e.g., adding an item to a shopping cart). Complex controllers might use the Command pattern to encapsulate actions.
  4. The Controller then instructs the appropriate View object to update the user interface. The View retrieves the necessary data from the Model to generate the UI, reflecting any changes in the Model (e.g., displaying the updated shopping cart contents). The Model should not have direct knowledge of the View. However, the Observer pattern can be used to allow the Model to notify registered Views of changes indirectly. A View object registers with the Model to be notified of changes, but the Model itself remains unaware of the specific View. Note: In some implementations, the View does not access the Model directly; instead, the Controller retrieves data from the Model and passes it to the View.
  5. The user interface waits for the next user interaction, restarting the cycle.