I have a PreferenceScreen in which the user is capable, if system can't autodetect it, to enter the device's phone number. I'm still learning this part of Android but I managed to understand a bit of PreferenceScreens by examples provided by Android SDK itself and a few tutorials.

What I want is that the user can save the phone number only if null or valid, where by "valid" I mean running a generic validation logic (ie. an anonymous method that returns true or false, that can be reused in any possible situation*) or better, just to simplify things, ^(\+39)?3[0-9]{9}$

For now I have the following XML snip

<EditTextPreference
    android:inputType="phone"
    android:key="@string/preference_phoneNo"
    android:selectAllOnFocus="true"
    android:singleLine="true"
    android:summary="@string/pref_phoneNumber_description"
    android:title="@string/pref_phoneNumber" />

and following code by courtesy of Eclipse New Activity wizard:

private void setupSimplePreferencesScreen() {
    if (!isSimplePreferences(this)) {
        return;
    }

    addPreferencesFromResource(R.xml.pref_general);
    bindPreferenceSummaryToValue(findPreference(getString(R.string.preference_phoneNo)));

}

addPreferenceFromResource is supposed to load the XML node and add the preference to the screen, while binPreferenceSummaryToValue is supposed to make description text change when preference is updated. Just for sake of completeness for those who don't like code courtesy of the IDE, the second method is provided by Eclipse who also provides a private class in the code file that is

     /**
 * A preference value change listener that updates the preference's summary
 * to reflect its new value.
 */

In the general case, what should I do to perform validation logic before the preference gets saved when I click OK on the preference editor? Where is the validation logic to be put in a PreferenceScreen?

*Aren't we all here to learn?