Android : Returning information from an AlertDialog in Android

I have created the following AlertDialog. In it the user selects a range of options stored in an XML file and handled using an adapter, then can click either the positive button or the negative button. Here is the code:

public void OpenDialog() {
        AlertDialog.Builder dialog = new AlertDialog.Builder(activity);
        dialog.setTitle("Promotion Options");
        LayoutInflater inflater = (LayoutInflater) activity.getSystemService(activity.LAYOUT_INFLATER_SERVICE);
        View v = inflater.inflate(com.zlaporta.chessgame.R.layout.promotion, null);

        dialog.setView(v);
        dialog.setPositiveButton("Choose", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                if (which == 1) {
                    System.out.println("ok");
                }
            }
        });
        dialog.setNegativeButton("Undo Move", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {

            }
        });
        dialog.show();

        Spinner spinner = (Spinner) v.findViewById(com.zlaporta.chessgame.R.id.promotionSpin);

        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(activity, com.zlaporta.chessgame.R.array.option,
                android.R.layout.simple_spinner_item);
        //could be other options here instead of simple_spinner_dropdown_item. Just type simple and see what comes up next time
        adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

        spinner.setAdapter(adapter);

        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {

            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

            }
        });
    }

Now, I'd like information about the user's selection in the spinner to be passed back to the enclosing activity after the positive button is clicked. What's the best way to do this?