How to prevent custom views from losing state across screen orientation changes

Question

I\'ve successfully implemented onRetainNonConfigurationInstance() for my main Activity to save and restore certain critical components across screen orientation

Answer 1

Instead of using onSaveInstanceState and onRestoreInstanceState, you can also use a ViewModel. Make your data model extend ViewModel, and then you can use ViewModelProviders to get the same instance of your model every time the Activity is recreated:

class MyData extends ViewModel {
    // have all your properties with getters and setters here
}

public class MyActivity extends FragmentActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // the first time, ViewModelProvider will create a new MyData
        // object. When the Activity is recreated (e.g. because the screen
        // is rotated), ViewModelProvider will give you the initial MyData
        // object back, without creating a new one, so all your property
        // values are retained from the previous view.
        myData = ViewModelProviders.of(this).get(MyData.class);

        ...
    }
}

To use ViewModelProviders, add the following to dependencies in app/build.gradle:

implementation "android.arch.lifecycle:extensions:1.1.1"
implementation "android.arch.lifecycle:viewmodel:1.1.1"

Note that your MyActivity extends FragmentActivity instead of just extending Activity.

You can read more about ViewModels here:

• Android Developer Guide, Handle configuration changes
• Android Developer Guide, Saving UI States, Use ViewModel to handle configuration changes
• Tutorial ViewModels : A Simple Example