OnSharedPreferenceChangeListener is not called # 2

Ok, I started implementing this awful code from google android. OnSharedPreferenceChangeListener is not called. This is my code, can you consult?

Class definition:

private SharedPreferences sPrefs;
private PreferenceChangedListener prefsChangedListener;

I have a private inner class:

private class PreferenceChangedListener implements
        OnSharedPreferenceChangeListener {

    public void onSharedPreferenceChanged(
            SharedPreferences sharedPreferences, String key) {
        if (key == "highThreshold") {
            try {
                highThreshold = Float.parseFloat(sharedPreferences
                        .getString(key, "0"));
            } catch (Exception e) {
            }
        }
    }
}

I tried the following code in OnResume and registered the listener after running the "Voorkeuren" preference function. Both do not work.

sPrefs = getPreferences(MODE_PRIVATE);
prefsChangedListener = new PreferenceChangedListener(); 
sPrefs.registerOnSharedPreferenceChangeListener(prefsChangedListener );

I defined a Voorkeuren class that extends PreferenceActivity

public class Voorkeuren extends PreferenceActivity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.preferences);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_voorkeuren, menu);
        return true;
    }
}

What I open as follows:

Intent intent = new Intent(getBaseContext(),Voorkeuren.class);
startActivity(intent);

The class displays perfectly and stores values ​​between sessions. But my application should not be polled if the settings are stalled. Any ideas? I have something red about SharedPreferences.Editor, but I'm not sure how this is related.