Handle checked and then unchecked checkbox's value in listview android

In my activity I have 4 items in a list view with checkboxes in each row. After I leave activity I want all the checked item position numbers in an arraylist. This code works fine when user clicks all the checkboxes ones and leave the activity. But when user clicks a checkbox and then unchecks it, item position is arraylist doesnt able to clear. This methood is in my CustomAdapter class.

class GameAdapter extends BaseAdapter{
  private ArrayList<Integer> positions = new ArrayList<Integer>();
  public ArrayList<Integer> getPositions() {
      return positions;
  }

getView(....){
 final ViewHolder holder;
 holder.checkBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {

            if(holder.checkBox.isChecked()) {

                positions.add(position);

            }
        }
    });
}
}

I am handling this adapter class in the activity where my listview resides. There I am taking this arraylist values like this

ArrayList<Integer> gamePositions = mGameAdapter.getPositions();
String itemNumbers = gamePositions.toString();

in itemNumber string I want all the checked item number values.

Thank you in advance for guidance....