MVVM (Model - View - ViewModel) is a software architectural pattern commonly used in application development. The main goal of MVVM is to completely separate the user interface from business logic, making it easier to develop, maintain, and test applications.
Main components of MVVM
MVVM consists of three main components that interact with each other:
- Model: Represents data and business logic. It has no knowledge of the View or ViewModel. The Model is responsible for retrieving and storing data, typically through APIs or a database.
- View: The user interface that users interact with. It displays data and sends user actions (such as button clicks) to the ViewModel. The View references the ViewModel but has no knowledge of the Model.
- ViewModel: The intermediary that connects the View and the Model. The ViewModel exposes data from the Model for the View to display. It handles requests from the View and interacts with the Model to fetch or update data. The ViewModel does not reference the View, which keeps it independent of any specific UI platform (e.g., Android, iOS, Windows).
Advantages of using MVVM
- Separation of concerns: MVVM clearly separates the UI from business logic, allowing UI and logic developers to work independently.
- Easy to test: Because the ViewModel does not depend on the View, it can be unit tested independently and easily.
- Reusability: A ViewModel can be reused across multiple Views as long as those Views need to display the same type of data or execute the same kind of logic.
- Simplified state management: The ViewModel helps manage application state more effectively, especially in configuration changes (such as device rotation).
Disadvantages of using MVVM
- Initial complexity: For small and simple applications, adopting MVVM can feel unnecessary and increase the initial complexity of the project.
- More code: Splitting responsibilities into separate classes can lead to more files and classes compared to simpler approaches, which can be challenging for beginners.
- Risk of an overloaded ViewModel: Without care, the ViewModel can become too large and contain too much logic (often called a ‘massive ViewModel’). This undermines the model’s clarity and maintainability. To avoid this, use Services to extract complex business logic.
- Debugging challenges: Due to automatic data binding mechanisms, tracing data flow can be more complex, especially when there are many two-way bindings.