Android Checkbox preference

I cannot find any tutorials on checkbox preference. I can use a listpreference, but I can't use checkbox preference. For now, I want that if user sets on the checbox, a toast msg says "true" and if he sets it off, the toast msg says "false". So far I have this:

preferences.xml:

 <CheckBoxPreference
          android:title="Show Call UI"
          android:defaultValue="true"
          android:summary="Show Call Interface when clicking call button"
          android:key="checkboxPref" />

EditPreferences.java:

public class EditPreferences extends PreferenceActivity {

    String listPreference;
    boolean checkboxPreference;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.preferences);
    }

    public void onStart(Intent intent, int startId) {
        getPrefs();
    }

    private void getPrefs() {
        SharedPreferences prefs = PreferenceManager
                .getDefaultSharedPreferences(getBaseContext());
        listPreference = prefs.getString("listPref", "nr1");
        checkboxPreference = prefs.getBoolean("checkboxPref", true);
    }
}

Edit: Solution thanks to David Caunt:

checkboxPreference.
    setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {

    public boolean onPreferenceChange(Preference preference, Object newValue) {
        if (newValue.toString().equals("true")) {
            Toast.makeText(getApplicationContext(), "CB: " + "true",
                                                    Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(getApplicationContext(), "CB: " + "false",
                                                    Toast.LENGTH_SHORT).show();
        }
        return true;
    }
});