The Model-View-Controller (MVC) is one of the classic architectural patterns from the book ““. It addresses interactive applications with a  flexible human-machine interface.

The MVC divides the program logic of a user interface into separate components model, view, and controller. The model manages the data and rules of the application. The view represents the data, and the controller interacts with the user.

Model-View-Controller

Purpose

• User interfaces need to be changed frequently
• Different user interfaces must be supported
• The data model is stable

Solution

• The application is divided into the components Model (data model), View (output components), and Controller (input components)
• Multiple output components can use the same data model

Structure

Model

• The central component of the pattern
• Contains the data (and the business logic)
• Is independent of the View and Controller

View

• Is responsible for the representing of the data and user interaction
• Observes the Model
• A View is associated with a Controller to manipulate the Model

Controller

• Manages one or more Views
• Accepts user interactions and prepares them for the Model or View
• Observes the Model
• Implements the update logic

There are two exciting aspects of the MVC: initialization and user input:

Initialization

The following steps happen during the initialization of the MVC:

• The model is created, and it initializes its data
• The view is created and observes the Model
• The controller is created and gets references to the model and the view; it observes the model
• The application starts event processing

User Input

In case of a user event, the following steps happen:

• The controller accepts the user input, handles them, and triggers the model
• The model changes its internal data
• The model notifies all views and controllers about the change of the internal data
• The views and controller update themself
  • If the PIN is entered incorrectly in an ATM for the third time, this can mean: The display shows that your account is locked. The ATM confiscates your debit card
• The controller continues to process events

Example

The following program mvc.cpp applies the MVC.

// mvc.cpp

#include 
#include 
#include 


class DefectModel {
 public:                                                                      // (5)
     mutable std::unordered_map<std::string, std::string> defects_ = { {"XYZ" , "File doesn't get deleted."},
                                                                       {"XAB" , "Registry doesn't get created."},
                                                                      {"ABC" , "Wrong title get displayed."} };

    std::string getDefectComponent(const std::string& component) const {
        return defects_[component];
    }

    int getSummary() const {
        return defects_.size();
    }

    std::unordered_map<std::string, std::string> getAllDefects() const {
        return defects_;
    }

};

class DefectView {
 public:
    void showSummary(int num) con