Qt ：非window子窗體的透明度設置

問題的由來

心血來潮，想利用QTimer 配合 setWindowOpacity()方法來實現一個窗體淡入的效果。

實驗代碼

粗糙的實驗代碼：

1. void Widget::on_pushButton_clicked()
2. {
3. QTimer *timerOpacity = new QTimer(this);
4. connect(timerOpacity,SIGNAL(timeout()),this,SLOT(changeOpacity()));
5. timerOpacity->start(100);
6. }
8. void Widget::changeOpacity()
9. {
10. if (opalevel > 8) return;
11. double opacity[9] = {0.9,0.8,0.7,0.6,0.5,0.4,0.3,0.2,0.1};
12. ui->stackedWidget->setWindowOpacity(opacity[opalevel]);
13. ui->widget->setWindowOpacity(opacity[opalevel]);
14. this->setWindowOpacity(opacity[opalevel]);
16. qDebug()<<"opalevel = "<< opalevel <<" ui->widget opacity:"<<ui->widget->windowOpacity();
17. qDebug()<<"opalevel = "<< opalevel <<" ui->stackedWidget opacity:"<<ui->stackedWidget->windowOpacity();
18. qDebug()<<"opalevel = "<< opalevel <<" ui opacity : "<< this->windowOpacity()<<endl;
19. }

實驗失敗

現象是主窗體的有淡入的效果，即透明度有變化，但是子窗體沒有，opacity始終為1 。
Log ：
opalevel = 0 ui->widget opacity: 1
opalevel = 0 ui->stackedWidget opacity: 1
opalevel = 0 ui opacity 0.898039
......

opalevel = 8 ui->widget opacity: 1
opalevel = 8 ui->stackedWidget opacity: 1
opalevel = 8 ui opacity 0.0980392

失敗原因

1. void QWidget::setWindowOpacity(qreal opacity)
2. {
3. Q_D(QWidget);
4. if (!isWindow())
5. return;
6. //...
7. }