The Model-View-ViewModel (MVVM) architecture is a software design pattern that provides a clear separation between the graphical user interface and the business logic of an application. This structure ensures that the user interface does not interact directly with the business logic, increasing the usability and organization of the application.
Data flow in MVVM
Data flow in MVVM is a key principle that keeps an application organized and maintainable. For example, pressing a button triggers an event in the View layer, which is then passed to the ViewModel. The ViewModel processes this event and updates the model accordingly. The model then handles the data persistence and business logic, resulting in a cyclical data flow that supports the user interface updates. This pattern effectively hides the business and validation logic from the View tier, ensuring a clear separation of concerns.
Model, View and ViewModel interaction
The interaction between Model, View, and ViewModel forms the basis of the MVVM architecture. Each of these components plays a separate role in the application. The Model handles data storage and business logic, serving as the server side of the application. ViewModel, acting as the model platform, handles user interactions and updates the model. On the other hand, the View provides the user interface by presenting data and accepting user input. This separation of roles in the architecture ensures efficient data flow and interaction within the computer software.
Delving into the code levels of MVVM
The MVVM architecture is divided into three key layers of code: the model, the view, and the view model. The Model tier is responsible for abstracting data sources, working together with the ViewModel to retrieve and store data. The View layer informs the ViewModel about user actions and observes changes in the ViewModel, but does not contain any program logic or user interface logic. The ViewModel layer opens data streams related to the View and serves as a link between the Model and the View. This multi-tiered structure facilitates the separation of tasks, improving the maintainability and scalability of the application.
Presentation tier
The presentation layer in the MVVM architecture is crucial for the user’s interaction with the application. This layer contains components such as activities, snippets, and view models. The role of the Activity is to facilitate communication between the user and the application, while the ViewModel is responsible for interacting with the domain layer to perform actions. It is important that the Activity should be as simple as possible, and all business logic should be encapsulated in the ViewModel. Such a division of tasks ensures the system’s modularity and efficiency, providing more focused development and easier debugging. In this process, creating a flawless user interface is extremely important.
Domain level
In the MVVM architecture, the domain layer is responsible for processing application use cases. It is here that actions are defined and executed, forming the main business logic of the system. This layer consists of abstract classes known as UseCases, which are extended by other classes to perform specific actions. The UseCaseHandler manages the execution of these use cases, ensuring that data retrieval actions do not block the user interface. The goal is to execute these actions in the background thread and deliver the response in the main thread, thus maintaining a seamless user experience.
Data layer
The data tier is an integral part of the MVVM architecture where all the repositories that interact with the domain tier are contained. This layer provides a data source API that the domain layer can use to retrieve or store data. The data tier decides whether to retrieve data from a local database or a remote server, thus providing flexibility and optimizing performance. The use of a binding adapter further simplifies the process of binding data between the data tier and the user interface, making the process more efficient and maintainable.
Advantages of MVVM architecture
The MVVM architecture, originally introduced by John Gossman, offers numerous advantages that have led to its widespread adoption by developers to create reliable and scalable applications. The architecture promotes code reuse, greatly simplifying the process of creating simple user interfaces. By separating the business logic from the user interface, MVVM facilitates independent testing of each layer, which ensures more reliable applications. The architecture also supports dependency injection, which provides better modularity and easier maintenance. With opportunities for increased code reuse and improved team collaboration, MVVM is the preferred choice for modern application development.