The Model-View-ViewModel (MVVM) pattern is a software design pattern used to separate the presentation layer from the business logic in a WPF (Windows Presentation Foundation) application. This pattern was designed specifically for WPF, but it can be applied to any .NET platform, including C#. The MVVM is a variation of the Model-View-Controller (MVC) pattern and is used to separate the user interface logic from the business logic. In MVVM, the Model represents the data and the business logic, the View is the user interface, and the ViewModel is a mediator between the Model and the View. The ViewModel is responsible for exposing the data from the Model to the View, and it also takes care of any UI-related logic, such as handling user input and displaying data to the user. This allows the View to be completely unaware of the underlying Model and business logic, making it easier to maintain and test the application. To implement MVVM in C#, you will need to create a ViewModel class and a View class, and then bind the View to the ViewModel using data binding. Here is an example of a simple MVVM implementation in C#: Figure 1. Code Snippet on View, and View Model In the above example, the ViewModel class exposes a single property called "Message", which will be displayed in the View. The View is a WPF Window and sets its DataContext to an instance of the ViewModel. The DataContext is used to bind the View to the ViewModel. In the XAML code for the View, you can bind the ViewModel's "Message" property to a TextBlock control: Figure 2. Property Binding on View and View Model In this example, the TextBlock's Text property is bound to the ViewModel's "Message" property. When the ViewModel's "Message" property changes, the TextBlock's Text will automatically update to reflect the change. Figure 1. The function of the Separate Divisions In figure 1 above, each of the MVVM Sections are detailed below: Model: This component represents the data and the business logic of an application. It is the source of truth for the state of an application, and it is responsible for storing and managing the data used by the application. View: This component represents the user interface of an application, and it is responsible for rendering the data provided by the model to the user. The view is only concerned with the presentation of the data and should not contain any business logic. ViewModel: This component acts as a bridge between the model and the view. It is responsible for exposing the data from the model to the view in a format that is easily consumable, and for handling any actions initiated by the view. The ViewModel should not contain any information about the view, but it should provide the data and behavior that the view needs to display and manipulate the model. Figure 2. Data flow from View-to-View Model and Model In this diagram, the arrows indicate the flow of data and updates between the components. The Model contains the data and business logic of the application, and the ViewModel acts as an intermediary between the Model and View. The View displays the data from the ViewModel, and the ViewModel updates the View when the data changes. The key advantage of the MVVM pattern is that it provides a clean separation of concerns between the Model, View, and ViewModel. This makes it easier to manage and maintain complex user interfaces, particularly as the application grows in size and complexity. Additionally, it makes it easier to test the application, as the Model and ViewModel can be tested independently of the View. In summary, the MVVM pattern is a powerful architectural pattern for building user interfaces and is well-suited for modern UI frameworks. By following the MVVM pattern, developers can enjoy the benefits of a clean, maintainable codebase, and can more easily test and debug their applications The Stepwise creation of the Model-View-ViewModel Pattern Step 1: Create a ViewModel class. The ViewModel is the core of the MVVM pattern and acts as the intermediary between the Model and the View. It holds the data that needs to be displayed in the View and provides methods for updating the Model. Step 2: Define the Model. The Model represents the data and the business logic of your application. It should contain the data that needs to be displayed in the View, and any methods or operations that manipulate that data. Step 3: Connect the View and ViewModel Once the ViewModel and Model are defined, the next step is to connect the View and ViewModel. This can be done using data binding, which is a mechanism that automatically updates the View when the data in the ViewModel changes. Step 4: Implement the View The View is responsible for displaying the data in the ViewModel. It should be designed to be as simple as possible, and should only contain the necessary UI elements for displaying the data. Summary Model-View-ViewModel (MVVM) is a design pattern used in software development that separates an application into three distinct components: model, view, and view model. The purpose of this separation is to make the code more maintainable and testable, and to separate concerns.