PATTERN
MVVM
MVVM (Model-View-ViewModel) is an architectural pattern that facilitates the separation of an application’s concerns – data presentation (View), interaction logic (ViewModel), and data management (Model). It’s primarily used in conjunction with data binding, allowing automatic synchronization of data between the ViewModel and the View. This reduces boilerplate code and enhances testability.
The pattern aims to create a cleaner coding separation and to simplify functional testing. The ViewModel exposes data needed by the View, and commands/methods the View can bind to for actions. The View remains passive, delegating interaction handling to the ViewModel. Changes to the Model are reflected in the ViewModel, and consequently in the View, through data binding.
Usage
MVVM is especially prominent in modern UI frameworks, providing a structured approach to building maintainable and scalable applications. It’s frequently used in:
- Desktop Applications: WPF, UWP, and other .NET-based desktop frameworks.
- Mobile Applications: iOS (using SwiftUI or UIKit), Android (using Jetpack Compose or Data Binding), and cross-platform frameworks like Xamarin and React Native.
- Web Applications: While sometimes debated, MVVM principles are employed through libraries like Vue.js, Angular, and Knockout.js.
- Any UI-driven application where a clear separation of concerns is desired for increased maintainability and testability.
Examples
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WPF (Windows Presentation Foundation): In WPF, developers commonly implement MVVM using data binding features. A
UserControl(the View) binds its UI elements (textboxes, labels, buttons) to properties and commands exposed by aViewModel. TheViewModelretrieves data from aModel(e.g., a database entity) and transforms it for display. For example, a simple form for editing user data would have a View representing the form, a ViewModel containing the user data and validation logic, and a Model representing theUserclass itself. -
SwiftUI (Apple’s UI framework): SwiftUI heavily leverages the MVVM pattern alongside its
@ObservedObjectand@Stateproperty wrappers for automatic UI updates. AViewobserves properties within aViewModeland updates its display when those properties change. Interactions from the UI trigger methods on theViewModel, which then interacts with theModel. For instance, an iOS app displaying a list of tasks could use aTaskListViewModelto manage the task data fetched from aTaskmodel, and the SwiftUIListview would bind to thetasksarray in the ViewModel.