Android : Edit default shared preferences

Im having an issue with editing the DefaultSharedPreferences. Indded, I have a method that I call regularly and I would like to use its input to edit the default shared preferences.

Here is what I tried but doesn't seem to work:

 mSharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
    SharedPreferences.Editor editor = mSharedPreferences.edit();
    editor.putString(getString(R.string.pref_location_default), stringCoordinates);
    editor.commit();

And here are my concerned Strings:

<!-- Key name for storing location in SharedPreferences [CHAR LIMIT=NONE] -->
<string name="pref_location_key" translatable="false">location</string>

<!-- Default postal code for location preference [CHAR LIMIT=NONE] -->
<string name="pref_location_default" translatable="false">-34.8799074,174.7565664</string>

Can someone help me please?

Thx!