public class AppsFlyerUtils implements AppsFlyerConversionListener {
    private static AppsFlyerLib sTracker;
    private static AppsFlyerUtils sInstance;
    private static WeakReference<Context> mContextReference;

    private AppsFlyerUtils(Application application, boolean debug) {
        mContextReference = new WeakReference<>(application.getApplicationContext());

        if (sTracker == null) {
          sTracker = AppsFlyerLib.getInstance();
        }

        sTracker.setGCMProjectNumber(mContextReference.get(), App.getResString(R.string.appsflyer_server_api_key));
        sTracker.startTracking(application, App.getResString(R.string.appsflyer_dev_key));
        sTracker.registerConversionListener(mContextReference.get(), this);

        . . .
    }

    public static void initialize(Application application, boolean debug) {
        if (sInstance == null) {
            sInstance = new AppsFlyerUtils(application, debug);
        }
    }

    @Override
    public void onInstallConversionDataLoaded(Map<String, String> map) {
        // This gets called every time.
    }

    @Override
    public void onAppOpenAttribution(Map<String, String> map) {
        // Never gets called.
    }

    . . .
}