PrefsFragment.java

package com.tikal.share;

import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.content.SharedPreferences.OnSharedPreferenceChangeListener;
import android.os.Bundle;
import android.preference.PreferenceFragment;

public class PrefsFragment extends PreferenceFragment implements OnSharedPreferenceChangeListener {
	@Override
    public void onCreate(Bundle savedInstanceState) {
    	super.onCreate(savedInstanceState);
        // Load the preferences from an XML resource
        addPreferencesFromResource(R.layout.pref);
    }
	
	@Override
	public void onResume() {
	    super.onResume();
	    getPreferenceManager().getSharedPreferences().registerOnSharedPreferenceChangeListener( this);

	}

	@Override
	public void onPause() {
	    getPreferenceManager().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);
	    super.onPause();
	}

	@Override
	public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
			String key) {
		if(key.equals("userName") && "".equals(sharedPreferences.getString(key, ""))){
			Editor editor = sharedPreferences.edit();
			editor.putString(key, "default");
			editor.commit();
		}
		
	}
}