How to save state during orientation change in Android if the state is made of my classes?

user_138606 0
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I was looking at the way Android handles orientation change for my application (I discovered that it restarts the mainactivity on orientation change. I've seen that you can override the method 

protected void onSaveInstanceState(Bundle outState)

To save stuff, then have the in onStart. The problem is that I've my view with custom objects and a listview using a custom adapter. Everything is in a ArrayList of these objects, but I've noticed that you can't put arbitrary objects in the bundle! So how do I save the state?

android
6 Answers

For simple data, the activity can use the onSaveInstanceState() method and restore its data from the bundle in onCreate(), but this approach is only suitable for small amounts of data that can be serialized then deserialized, not for potentially large amounts of data like a list of users or bitmaps.

The ViewModel class allows data to survive configuration changes such as screen rotations.
Architecture Components provides ViewModel helper class for the UI controller that is responsible for preparing data for the UI.

**Example**:

if you need to display a list of users in your app, make sure to assign responsibility to acquire and keep the list of users to a ViewModel, instead of an activity or fragment, as illustrated by the following sample code.

public class MyViewModel extends ViewModel {
    private MutableLiveData<List<User>> users;
    public LiveData<List<User>> getUsers() {
        if (users == null) {
            users = new MutableLiveData<List<User>>();
            loadUsers();
        }
        return users;
    }

    private void loadUsers() {
        // Do an asynchronous operation to fetch users.
    }
}

public class MyActivity extends AppCompatActivity {
    public void onCreate(Bundle savedInstanceState) {
        // Create a ViewModel the first time the system calls an activity's onCreate() method.
        // Re-created activities receive the same MyViewModel instance created by the first activity.

        MyViewModel model = ViewModelProviders.of(this).get(MyViewModel.class);
        model.getUsers().observe(this, users -> {
            // update UI
        });
    }
}
user_32434920
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