qt中如何画图，使用QPainter，提示QPainter is not active

[weixin_38048397]

如题，我只需要在窗体的一个指定区域内刷为黑色，我在程序中调用QPainter，提示QPainter is not active，难道QPainter只能在PaintEvent中才能调用吗。代码如下，请高手帮忙指点，我要的效果只是刷为黑色，用其他方法也行：void MainWindow::initLogo(){    /* brush a black background */    QPainter paint(this);    paint.setPen(QPen(Qt::black));    paint.setBrush(QBrush(Qt::black, Qt::SolidPattern));    paint.drawRect(10, 20, this->width() - 20, this->height() - 30);    .......}