android sharedpreferences: null pointer exception

I'm no expert but I'll try to help.

The format to save SharedPreferences is like this example:

SharedPreferences settings = getSharedPreferences("MY_PREFS", MODE_PRIVATE);
SharedPreferences.Editor editor = settings.edit();
editor.putBoolean("audio_playing", true);
editor.commit();

And the format to retrieve SharedPreferences is like this:

SharedPreferences settings = getSharedPreferences("MY_PREFS", MODE_PRIVATE);        
boolean audio_playing = settings.getBoolean("audio_playing", false);

So I'd rewrite what you have something like this:

SharedPreferences mPrefs = getSharedPreferences("xyz", 0);
SharedPreferences.Editor ed = mPrefs.edit();
ed.putString("names", names);
ed.putString("numbers", numbers);
ed.commit();

And then to retrieve the value:

SharedPreferences mPrefs = getSharedPreferences("xyz", 0);
String name = mPrefs.getString("names","");
String number = mPrefs.getString("numbers),"");

I hope this helps. If not, oh well I tried.

 // add this inside onCreate Method

pref = getSharedPreferences("user_details",MODE_PRIVATE);

// Your Modified Code is :

protected void onPause() {
    super.onPause();

SharedPreferences.Editor ed = mPrefs.edit();
    ed.putString("names", names);
    ed.putString("numbers", numbers);
    ed.commit();
}   

@Override
protected void onResume() {
    // TODO Auto-generated method stub
    super.onResume();

    SharedPreferences mPrefs = getSharedPreferences("user_details", Context.MODE_PRIVATE);
    mPrefs.getString("names", "");
    mPrefs.getString("numbers", "");

}