How to edit ArrayList in MainActivity from second activity

I have an ArrayList in MainActivity, and I want to modify that list in ActivityB. How would I achieve this?

My current solution is that I made the ArrayList a static variable so that I can access it in ActivityB using MainActivity.ArrayList. However, I have seen that this may not be good practice and is not good information hiding. This list is the only static variable I have. Could I keep using this method or would it be better if I did something else? If so, how else could I do this?

Maybe You can try to send this array from MainActivity to SecondActivty and in Your SecondActivity when You change that array in the way You want You can send it back and to MainActivity? This is sample code, I am sending int ( named myValue) from MainActivity to SecondActivity and change it there. And then send it back to MainActivity

MainActivity:

public class MainActivity extends AppCompatActivity
{
private static final int LAUNCH_SECOND_ACTIVITY = 1;
public static final String MY_VALUE_KEY = "MY_VALUE_KEY";
private int myValue = 1;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Log.d("MyTag", "MAIN ACTIVITY. On create, myValue = " + myValue);
findViewById(R.id.buttonGoToSecond).setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View view)
{
startSecondActivity();
}
});
}
private void startSecondActivity()
{
Intent i = new Intent(this, SecondActivity.class);
i.putExtra(MY_VALUE_KEY, myValue);
startActivityForResult(i, LAUNCH_SECOND_ACTIVITY);
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data)
{
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == LAUNCH_SECOND_ACTIVITY)
{
if (resultCode == Activity.RESULT_OK)
{
myValue = data.getIntExtra(MY_VALUE_KEY, -1);
Log.d("MyTag", "MAIN ACTIVITY. Result, myValue = " + myValue);
}
else if (resultCode == Activity.RESULT_CANCELED)
{
Log.d("MyTag", "No result");
}
}
}
}

SecondActivity:

public class SecondActivity extends AppCompatActivity
{
private int dataFromMain;
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_second);
// Get data from MainActivity
dataFromMain = getIntent().getIntExtra(MainActivity.MY_VALUE_KEY, -1);
Log.d("MyTag", "SECOND ACTIVITY. Data retrieved: " + dataFromMain);
//Do something with data
dataFromMain *= 2;
findViewById(R.id.buttonGoToMain).setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View view)
{
goToMain();
}
});
}
private void goToMain()
{
Intent returnIntent = new Intent();
Log.d("MyTag", "SECOND ACTIVITY. Data send back: " + dataFromMain);
returnIntent.putExtra(MainActivity.MY_VALUE_KEY, dataFromMain);
setResult(Activity.RESULT_OK, returnIntent);
finish();
}
}

And the logs look like this:

D/MyTag: MAIN ACTIVITY. On create, myValue = 1
D/MyTag: SECOND ACTIVITY. Data retrieved: 1
D/MyTag: SECOND ACTIVITY. Data send back: 2
D/MyTag: MAIN ACTIVITY. Result, myValue = 2