QPainter 无法显示图像？解决办法

QPainter 无法显示图像？？
我创建了一个项目，继承于QWidget，在构造函数中添加如下代码：

C/C++ code

    QPainter painter(this); QPixmap pix;     pix.load(":/Rotate/Resources/loading.png");        //painter.translate(50,50);                //使图片的中心作为旋转的中心    // painter.rotate(90);                //顺时针旋转90°  //painter.translate(-50,-50);        //将原点复位  painter.drawPixmap(0,0,100,100,pix);

可是现实不出该图片？求解！！

------解决方案--------------------
Warning: When the paintdevice is a widget, QPainter can only be used inside a paintEvent() function or in a function called by paintEvent(); that is unless the Qt::WA_PaintOutsidePaintEvent widget attribute is set. On Mac OS X and Windows, you can only paint in a paintEvent() function regardless of this attribute's setting.

你既然是在构造函数中添加的就看看这段话！