public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        context = getApplicationContext();
        CreateNotification notification = new CreateNotification();
        notification.create(context);
    }

public boolean onPreferenceClick(Preference preference) {
                if (sharedPrefs.getBoolean("notification", false)) {
                //zugriff auf CreateNotification.create();
                }else{
                //zugriff auf CreateNotification.delete();
                }

public void create(Context context) {
        sharedPrefs = PreferenceManager.getDefaultSharedPreferences(context);

        if (sharedPrefs.getBoolean("notification", false)) {
            mManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);

      ....
        }
    }

    public void delete() {
        Log.d("","delete");
        // else {
        try {
            mManager.cancel(notify_id);
        } catch (Exception e) {

            // }
        }
    }