QT4怎么给QMainWindow增加背景图片啊

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    //设置编码,显示中文
    QTextCodec::setCodecForTr( QTextCodec::codecForName("GB2312") );

      
    COrderComm oOdCm;
    oOdCm.showMaximized();   
    
    return a.exec();
}

COrderComm::COrderComm(QWidget  *parent)
    : QMainWindow(parent)
    {

    //这里如何加在背景图片啊

    }

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QPalette palette;
    palette.setBrush(QPalette::Background, QBrush(QPixmap("1.jpg")));
    this->setPalette(palette);
}