What is the working principle of Android ViewModel?

The Android ViewModel is a class used to manage UI-related data, working primarily through the following steps:

1. Create a ViewModel: Create a subclass of ViewModel in the Activity or Fragment, and define the data that needs to be managed and related methods in this class.
2. Bound to the UI lifecycle: The ViewModel is bound to the lifecycle of the UI component (such as an Activity or Fragment), so when the UI component is destroyed, the ViewModel is also destroyed.
3. Caching data: ViewModel saves the data before being destroyed, so it can be restored when recreated to prevent data loss during changes like screen rotation.
4. Provide data to UI: The ViewModel supplies data to UI components for display on the interface. UI components can access and update the data by observing the LiveData in the ViewModel or using Data Binding.
5. Handling business logic: ViewModels can incorporate certain business logic, responsible for managing user interactions and data operations. This logic helps UI components stay focused on displaying the interface, preventing an overload of code logic.

By using ViewModel, the separation of UI components and data is achieved, improving the testability and maintainability of the code, and also better handling situations such as device configuration changes.