Handle configuration changes

Some device configurations can change during runtime (such as screen orientation, keyboard availability, and when the user enables multi-window mode). When such a change occurs, Android restarts the running Activity ( onDestroy()is called, followed by onCreate()). The restart behaviour is designed to help your application adapt to new configurations by automatically reloading your application with alternative resources that match the new device configuration.

To properly handle a restart, it is important that your activity restores its previous state. You can use a combination of onSaveInstanceState(), ViewModel objects, and persistent storage to save and restore the UI state of your activity across configuration changes. For more information on how to save your Activity state, read Saving UI States.

To test that your application restarts itself with the application state intact, you should invoke configuration changes (such as changing the screen orientation) while performing various tasks in your application. Your application should be able to restart at any time without loss of user data or state in order to handle events such as configuration changes or when the user receives an incoming phone call and then returns to your application much later after your application process may have been destroyed. 

However, you might encounter a situation in which restarting your application and restoring significant amounts of data can be costly and create a poor user experience. In such a situation, you have two other options:

1. Retain an object during a configuration change

Allow your activity to restart when a configuration changes, but carry a stateful object to the new instance of your activity.

2. Handle the configuration change yourself

It is not recommended to handle configuration changes yourself due to the hidden complexity of handling the configuration changes. However, if you are unable to preserve your UI state using the preferred options (onSaveInstanceState(), ViewModels, and persistent storage) you can instead prevent the system from restarting your activity during certain configuration changes. Your app will receive a callback when the configurations do change so that you can manually update your activity as necessary.