onSharedPreferenceChanged not fired if change occurs in separate activity?

The OnSharedPreferenceChangeListener gets garbage collected in your case if you use an anonymous class.

To solve that problem use the following code in PreferenceActivity to register and unregister a change listener:

public class MyActivity extends PreferenceActivity implements
    OnSharedPreferenceChangeListener {

@Override
protected void onResume() {
    super.onResume();
    // Set up a listener whenever a key changes
    getPreferenceScreen().getSharedPreferences()
            .registerOnSharedPreferenceChangeListener(this);
}

@Override
protected void onPause() {
    super.onPause();
    // Unregister the listener whenever a key changes
    getPreferenceScreen().getSharedPreferences()
            .unregisterOnSharedPreferenceChangeListener(this);
}

public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,String key) 
{
  // do stuff
}

Furthermore be aware that the listener only gets called if the actual value changes. Setting the same value again will not fire the listener.

see also SharedPreferences.onSharedPreferenceChangeListener not being called consistently

This happen because garbage collector. its works only one time. then the reference is collected as garbage. so create instance field for listener.

private OnSharedPreferenceChangeListener listner;

listner = new SharedPreferences.OnSharedPreferenceChangeListener() {        
        @Override
        public void onSharedPreferenceChanged(SharedPreferences prefs, String key) {
            //implementation goes here
        }
    };
    prefs.registerOnSharedPreferenceChangeListener(listner);