MVVM

MVVM stands for Model-View-ViewModel, an architectural pattern used to separate the development of the graphical user interface from the development of the business logic. It divides an application into three core components: the Model, which represents the domain data and business rules; the View, which is the user interface; and the ViewModel, an abstraction of the View that exposes the data and commands the View can bind to.

In MVVM, the View binds to properties and commands exposed by the ViewModel rather than directly to the Model. This binding is typically two-way, so changes in the UI update the ViewModel and vice versa. The ViewModel implements presentation logic and state, often providing change notification, such as through INotifyPropertyChanged in .NET environments. The Model remains independent of the UI, allowing it to be reused and tested separately.

The pattern is especially associated with XAML-based UI frameworks, including WPF, Silverlight, Xamarin.Forms, and UWP, where data binding and command binding simplify the interaction between the View and ViewModel. MVVM helps improve testability by enabling unit tests for the ViewModel without requiring the View, and it supports design-time data to aid UI designers.

A common point of comparison is with MVC; MVVM tends to decouple the View further by introducing the ViewModel as an intermediary, reducing direct interactions between the View and the Model. While MVVM offers clear benefits in suitable contexts, it can introduce boilerplate and complexity, and may not be the best fit for all types of applications. The pattern has since influenced other frameworks and patterns, including Knockout.js and various MVVM-inspired approaches in modern web and cross-platform development.