scrollbar animation effect

[IknowQT]

I want to give an animation effect that makes the qScrollbar appear whenever I move it and hide it when it stops moving, how can I do that?
There is a user class that inherits Scrollbar, and we want to animate it by receiving the valuechanged signal.

void usrScrollBar::VisibleSlider(bool bShow)
{
	if (bShow)
	{
		auto anim = new QPropertyAnimation(this, "AnmFrameAlpha", this);
		anim->setDuration(2000);
		anim->setStartValue(0.00);
		anim->setEndValue(1.00);
		anim->start(QAbstractAnimation::DeleteWhenStopped);
	}
	else
	{
		auto anim = new QPropertyAnimation(this, "windowOpacity");
		anim->setDuration(2000);
		anim->setStartValue(1.00);
		anim->setEndValue(0.00);
		anim->start(QAbstractAnimation::DeleteWhenStopped);

		emit UserDefineFinishScroll();
	}

	this->setVisible(bShow);
}

qreal usrScrollBar::AnmFrameAlpha() const
{
	qDebug() << QString("AnmFrameAlpha : %1").arg(this->windowOpacity());
	return this->windowOpacity();
}

void usrScrollBar::SetAnmFrameAlpha(qreal rAlpha)
{
	this->setWindowOpacity(rAlpha);
	this->update();
}