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：

void Widget::on_pushButton_clicked()
{
 QTimer *timerOpacity = new QTimer(this);
 connect(timerOpacity,SIGNAL(timeout()),this,SLOT(changeOpacity()));
 timerOpacity->start(100);
}

void Widget::changeOpacity()
{
if (opalevel > 8) return;
double opacity[9] ={0.9,0.8,0.7,0.6,0.5,0.4,0.3,0.2,0.1};
    ui->stackedWidget->setWindowOpacity(opacity[opalevel]);
ui->widget->setWindowOpacity(opacity[opalevel]);
this->setWindowOpacity(opacity[opalevel]);

qDebug()<<"opalevel = "<< opalevel <<" ui->widget opacity:"<<ui->widget->windowOpacity();
qDebug()<<"opalevel = "<< opalevel <<" ui->stackedWidget opacity:"<<ui->stackedWidget->windowOpacity();
qDebug()<<"opalevel = "<< opalevel <<" ui opacity : "<< this->windowOpacity()<<endl;
}

✿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 =0ui->widget opacity: 1
opalevel =0ui->stackedWidget opacity: 1
opalevel =0ui opacity0.898039
......

opalevel =8ui->widget opacity: 1
opalevel =8ui->stackedWidget opacity: 1
opalevel =8ui opacity0.0980392

✿失败原因

void QWidget::setWindowOpacity(qreal opacity)
{
Q_D(QWidget);
if (!isWindow())
return;
//...
}

✿解决方案

QGraphicsOpacityEffect

// in the constructor
opacityEffect = new QGraphicsOpacityEffect;
ui->widget->setGraphicsEffect(opacityEffect);
...
// in changeOpacity()
opacityEffect->setOpacity(opacity[opalevel]);

✿效果图