View models

In C# and .NET, a view model is a design pattern used to separate the presentation logic and data from the actual model classes.

View models are primarily used in the context of user interfaces, such as web applications (ASP.NET MVC or ASP.NET Core MVC), desktop applications (WPF, WinForms), or mobile apps (Xamarin).

The key concepts related to view models, are:

1. Purpose of View Models:

• Separation of Concerns: View models help separate the concerns of the user interface from the business logic or data access. They act as intermediaries between the user interface and the underlying data models.
• Customized Data: View models allow you to shape and customize the data that is presented to the user. They can include properties, methods, and validation specific to the view’s needs.

1. Characteristics of View Models:

• Data Representation: View models represent data that is meant to be displayed or edited in a particular view, screen, or form. They may include only a subset of the properties from one or more data models.
• Presentation Logic: View models can contain presentation logic related to formatting, validation, and user-friendly data representation.
• Validation: They often include validation rules specific to the view, such as required fields or format constraints.
• UI State: View models may include properties to store the current state of the user interface, such as selected items, pagination settings, or sort orders.

1. Benefits:

• Flexibility: View models provide flexibility in shaping data for different views or screens. You can tailor the view model to match the specific requirements of each UI component.
• Testability: They simplify unit testing of the presentation logic because you can test it independently of the actual UI components.
• Maintainability: By separating concerns, view models contribute to the maintainability and readability of your codebase.

1. Usage in ASP.NET Core MVC:

• In ASP.NET Core MVC, view models are commonly used to pass data from controllers to views. Each view typically has its associated view model, which contains the data needed for rendering that view.
• View models are also used to collect data from user input (e.g., form submissions) and pass it back to controllers for processing.

Here’s a simplified example of a view model in an ASP.NET Core MVC application:

public class ProductViewModel
{
    public int ProductId { get; set; }
    public string ProductName { get; set; }
    public decimal Price { get; set; }
    public string Category { get; set; }
}

In this example, ProductViewModel represents a subset of data from a Product model and may include additional properties or validation rules specific to a product listing or editing view.

In summary, view models in C# and .NET are an essential concept for separating presentation concerns from data models, allowing to customize data for views and maintain clean and testable code in UI-related components.