Saving object reference in onSaveInstanceState using Serializable?

Question

I need clarification on how I can save the state of an object that has a reference to another object?

Lets say I have the below class objects that I need to save and restore:

public class ObjectA implements Serializable{
    private List<ObjectB> mObjectBList;
}

public clas ObjectB implements Serializable {
    // some other members here
    private ObjectA mParent;
}

Here are the code to invoke the save and restore in a fragment:

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putSerializable("ObjectA", mObjectA);
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    if (savedInstanceState != null) {
        mObjectA = (mObjectA) savedInstanceState.getSerializable("ObjectA");
    }
}

Questions:

1. Will saving mObjectA also save every object in mObjectBList?
2. Since mObjectB has a reference to its parent ObjectA, will ObjectA be re-instantiated for each ObjectB? Which then in turn will re-instantiate ObjectB, and then it will re-instantiate ObjectA, and so forth, leading to an infinite loop?
3. How would you solve this problem?

I'm not clear on what happens when an object gets saved as a Serializable, so please help me understand how Android distinguishes when to instantiate a new object and when it will reproduce an actual reference.

Answer 1

1. Yes. But List is not Serializable. Change List to ArrayList for example.

2. It works fine. Java serialization works for cyclic references. Here is similar question.

3. I think there is no problem.

I did test with following code.

public class MainActivity extends AppCompatActivity {

    private ObjectA mObjectA;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (savedInstanceState != null) {
            mObjectA = (ObjectA) savedInstanceState.getSerializable("ObjectA");
            // check mObjectA == mObjectA.getObjectBList().get(0).getParent();

        } else {
            mObjectA = new ObjectA();
            ArrayList<ObjectB> list = new ArrayList<>();
            list.add(createB());
            list.add(createB());
            list.add(createB());
            list.add(createB());
            list.add(createB());
            mObjectA.setObjectBList(list);
        }
    }

    private ObjectB createB() {
        ObjectB objectB = new ObjectB();
        objectB.setParent(mObjectA);
        return objectB;
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putSerializable("ObjectA", mObjectA);
    }
}

public class ObjectA implements Serializable {
    private ArrayList<ObjectB> mObjectBList;

    public void setObjectBList(ArrayList<ObjectB> objectBList) {
        mObjectBList = objectBList;
    }

    public ArrayList<ObjectB> getObjectBList() {
        return mObjectBList;
    }
}

public class ObjectB implements Serializable {
    // some other members here
    private ObjectA mParent;

    public void setParent(ObjectA parent) {
        mParent = parent;
    }

    public ObjectA getParent() {
        return mParent;
    }
}