MVVM pattern

Model–view–viewmodel (MVVM) is a software architectural pattern that facilitates the separation of the development of the UI - rom the development of the business logic or back-end logic (the model) so that the view is not dependent on any specific model platform.

The separate code layers of MVVM are:

Model: This layer is responsible for the abstraction of the data sources. Model and ViewModel work together to get and save the data.
View: The purpose of this layer is to inform the ViewModel about the user’s action. This layer observes the ViewModel and does not contain any kind of application logic.
ViewModel: It exposes those data streams which are relevant to the View. Moreover, it servers as a link between the Model and the View.

It is important to note that in MVVM, the view doesn’t maintain state information; instead, it is synchronized with the ViewModel. In MVVM, the ViewModel isolates the presentation layer and offers methods and commands for managing the state of a view and manipulating the model.

The view and the Viewmodel in the MVVM design pattern communicate using methods, properties, and events. The view and the Viewmodel have bi-directional data binding, or two-way data binding, which guarantees that the Viewmodel’s models and properties are in sync with the view.

Examples

MVVM Architecture - Android Tutorial for Beginners - Step by Step Guide

Guide to app architecture

Pokedex

Foodium

MVVM-Kotlin-Android-Architecture

Conclusion

Advantages:

Maintainability – Can remain agile and keep releasing successive versions quickly;
Extensibility – Have the ability to replace or add new pieces of code;
Testability – Easier to write unit tests against a core logic;
Transparent Communication – The view model provides a transparent interface to the view controller, which it uses to populate the view layer and interact with the model layer, which results in a transparent communication between the layers of your application.