漸漸顯示

    QPropertyAnimation *animation = new QPropertyAnimation(this, "windowOpacity");
    animation->setDuration(1000);
    animation->setStartValue(0);
    animation->setEndValue(1);
    animation->start();

漸漸關閉

QPropertyAnimation *animation = new QPropertyAnimation(this, "windowOpacity");
animation->setDuration(1000);
animation->setStartValue(1);
animation->setEndValue(0);
animation->start();
connect(animation, SIGNAL(finished()), this, SLOT(close()));