37.2 Implementing ViewModel State Saving
Basic ViewModel state saving is made possible through the introduction of the ViewModel Saved State library. This library essentially extends the ViewModel class to include support for maintaining state through the termination and subsequent relaunch of a background process.
The key to saving state is the SavedStateHandle class which is used to save and restore the state of a view model instance. A SavedStateHandle object contains a key-value map that allows data values to be saved and restored by referencing corresponding keys.
To support saved state, a different kind of ViewModel subclass needs to be declared, in this case one containing a constructor which can receive a SavedStateHandle instance. Once declared, ViewModel instances of this type can be created by including a SavedStateViewModelFactory object at creation time. Consider the following code excerpt from a standard ViewModel declaration:
package com.ebookfrenzy.viewmodeldemo...