Qt ：非window子窗体的透明度设置

✿问题的由来

心血来潮，想利用QTimer 配合 setWindowOpacity()方法来实现一个窗体淡入的效果。

✿实验代码

粗糙的实验代码：

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. }
7.
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]);
15.
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. }

✿实验失败

现象是主窗体的有淡入的效果，即透明度有变化，但是子窗体没有，opacity始终为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

✿失败原因

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

✿解决方案

QGraphicsOpacityEffect

1. // in the constructor
2. opacityEffect = new QGraphicsOpacityEffect;
3. ui->widget->setGraphicsEffect(opacityEffect);
4. ...
5. // in changeOpacity()
6. opacityEffect->setOpacity(opacity[opalevel]);

✿效果图