Dialog::Dialog(QWidget *parent) :

    QDialog(parent),

    ui(new Ui::Dialog)

{

    ui->setupUi(this);

    this->setParent(parent);

    this->setWindowFlags(Qt::CustomizeWindowHint|Qt::FramelessWindowHint);

    this->hide();

}

Dialog *dlg;

void MainWindow::on_pushButton_clicked()

{

    dlg=new Dialog(this);

    dlg->show();

    //在父窗体位置

    dlg->move(,);

    //子窗体大小

    dlg->resize(,);

}

void MainWindow::resizeEvent(QResizeEvent *e)

{

      int realWidth = this->width();

      int realHeight = this->height();

     if(dlg!=NULL)

     {

         dlg->resize(realWidth-,realHeight-);

     }

}