Using shared preferences listener.

gistfile1.java

public class MyApp extends Application { //This is the Android Application object...
//if your app exists, so does it, and you are guarenteed only one

private String mPrefA;
private String mPrefB;

private mPrefsChanged = false; //Guarded by "this"

@Override
public void onCreate() {
	//Fetch application preferences
	SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(this);
	prefs.registerOnSharedPreferenceChangeListener(this);
	mPrefA = prefs.getString(getString(R.string.pref_key_A), "");
	mPrefB = prefs.getString(getString(R.string.pref_key_B), "");
}

@Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
	synchronized(this) {
		if (key.equals(getString(R.string.pref_key_A))) {
			mPrefA = sharedPreferences.getString(getString(R.string.pref_key_A), "");
			mPrefsChanged = true;
		} else if (key.equals(getString(R.string.pref_key_B))) {
			mPrefB = sharedPreferences.getString(getString(R.string.pref_key_B), "");
			mPrefsChanged = true;
		}
	}
}

public boolean havePrefsChanged() {
	synchronized(this) {
		mPrefsChanged = false;
		return mPrefsChanged;
	}
}

//Getters and setters for your preferences here, though I recomend a single data object which you update/provide atomicly,
//otherwise there will be a lot of flag checking and you arent guarenteed of its thread safety. Alternatively, you could register
//a thread safe LIST of listeners with this class and notify them of each change.