How can I save an arraylist filled with objects of type person using onSaveInstanceState?

Question

I have this list:

private ArrayList<Person> people = new ArrayList<>();

And this list is filled with random people. Whenever I turn my screen, the list refreshes and a new list appears. I dont want this to happen.

I have tried to do this with the onSaveInstanceState method like this:

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putParcelableArrayList("key", people);
}

but i get the following error at people:

Required type: ArrayList <? extends Parcelable>
Provided: ArrayList<Person>

I am able to fix this error by changing the code to:

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putParcelableArrayList("key", (ArrayList<? extends Parcelable>) people);
}

But when I go to the onCreate method where I want to data to load I use this code:

if(savedInstanceState != null)
    {
        people = savedInstanceState.getParcelableArrayList("key");
    }

I get the following error:

Required type: ArrayList <Person>
Provided: ArrayList<Parcelable>

What can I do to make this work? Ive looked everywhere but cannot seem to find the solution. I just need the list to remain the same whenever the screen rotates.

Answer 1

There are a few possible ways to solve the problem:

• Save the list in onSaveInstanceState() by having your class Person implement the Parcelable interface. See the Android documentation about how to implement Parcelable (you will need to implement a few additional methods to save and restore the data in the Person instance.
• Use onRetainNonConfigurationInstance() and getLastNonConfigurationInstance(). You can return your list of Person objects in onRetainNonConfigurationInstance() and then you can retrieve it in onCreate() when your Activity is recreated (after Android kills it due to the orientation change).
• Declare the variable static, in which case it will not be reinitialized after Android kills your Activity and creates a new one. This is not the preferred method, but it is the simplest one.