mdiArea

　　　QMdiSubWindow *subWin = new QMdiSubWindow;

    showRuleDialog *showruleDialog=new showRuleDialog(this);

    subWin->setWidget(showruleDialog);

    subWin->setAttribute(Qt::WA_DeleteOnClose);

    ui->mdiArea->addSubWindow(subWin);

    subWin->show();