//create new child window and add up to QWorkspace then return a pointer
MdiChild *MainWindow::createMdiChild()
    {
        MdiChild *child = new MdiChild;
        workspace->addWindow(child);

        connect(child, SIGNAL(copyAvailable(bool)),
                cutAct, SLOT(setEnabled(bool)));
        connect(child, SIGNAL(copyAvailable(bool)),
                copyAct, SLOT(setEnabled(bool)));

        return child;
    }

//Get the current active window
MdiChild *MainWindow::activeMdiChild()
    {
        return qobject_cast<MdiChild *>(workspace->activeWindow());
    }
//Find the specify window
MdiChild *MainWindow::findMdiChild(const QString &fileName)
    {
        QString canonicalFilePath = QFileInfo(fileName).canonicalFilePath();

        foreach (QWidget *window, workspace->windowList()) {
            MdiChild *mdiChild = qobject_cast<MdiChild *>(window);
            if (mdiChild->currentFile() == canonicalFilePath)
                return mdiChild;
        }
        return 0;
    }

//update window menu
QList<QWidget *> windows = workspace->windowList();
        separatorAct->setVisible(!windows.isEmpty());

        for (int i = 0; i < windows.size(); ++i) {
            MdiChild *child = qobject_cast<MdiChild *>(windows.at(i));

            QString text;
            if (i < 9) {
                text = tr("&%1. %2").arg(i + 1)
                                    .arg(child->userFriendlyCurrentFile());
            } else {
                text = tr("%1. %2").arg(i + 1)
                                   .arg(child->userFriendlyCurrentFile());
            }
QAction *action  = windowMenu->addAction(text);
            action->setCheckable(true);
            action ->setChecked(child == activeMdiChild());
            connect(action, SIGNAL(triggered()), windowMapper, SLOT(map()));
            windowMapper->setMapping(action, child);
        }