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);}