public static void fadeIn(View view, float startAlpha, float endAlpha, long duration) {
        if (view.getVisibility() == View.VISIBLE) return;

        view.setVisibility(View.VISIBLE);
        Animation animation = new AlphaAnimation(startAlpha, endAlpha);
        animation.setDuration(duration);
        view.startAnimation(animation);
    }

    public static void fadeIn(View view) {
        fadeIn(view, 0F, 1F, 400);

        // We disabled the button in fadeOut(), so enable it here.
        view.setEnabled(true);
    }

    public static void fadeOut(View view) {
        if (view.getVisibility() != View.VISIBLE) return;

        // Since the button is still clickable before fade-out animation
        // ends, we disable the button first to block click.
        view.setEnabled(false);
        Animation animation = new AlphaAnimation(1F, 0F);
        animation.setDuration(400);
        view.startAnimation(animation);
        view.setVisibility(View.GONE);
    }