1、为当前主窗口设置背景图片

QSize size  = this->size();int width   = size.width();int height  = size.height();QPixmap pixmap("../src/B002.png"); //通过构造函数载入图片方式label1 = new QLabel(this);label1->resize(width,height);pixmap.scaled(label1->size(), Qt::KeepAspectRatio,Qt::SmoothTransformation);label1->setScaledContents(true);label1->setPixmap(pixmap);label1->setStyleSheet("QLabel { background-color: rgb(238, 238, 236); }");label1->show();

 上面设置的label1在widget类的私有变量里设置，因为下面重写拉伸事件要操作这个label1

2、拉伸屏幕的时候会触发什么事件

//触发void resizeEvent(QResizeEvent *event) override;void Widget::resizeEvent(QResizeEvent *event)
{qDebug() << "clicked" ;QWidget::resizeEvent(event);
}

3、如何刷新当前界面 

void Widget::resizeEvent(QResizeEvent *event)
{QSize size  = this->size();int width   = size.width();int height  = size.height();label1->resize(width,height);label1->show();QWidget::resizeEvent(event);
}

重写鼠标事件中添加了resize()函数，show函数，实现功能