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QXmlStream Bookmarks Example

The QXmlStream Bookmarks example provides a reader for XML Bookmark Exchange Language (XBEL) files using Qt's QXmlStreamReader class for reading, and QXmlStreamWriter class for writing the files.


XbelWriter Class Definition

The XbelWriter class is a subclass of
QXmlStreamReader, which provides an XML parser with a streaming API. XbelWriter also contains a private instance of QTreeWidget in order to display the bookmarks according to hierarchies.
class XbelWriter : public QXmlStreamWriter
{
public:
    XbelWriter(QTreeWidget *treeWidget);
    bool writeFile(QIODevice *device);

private:
    void writeItem(QTreeWidgetItem *item);
    QTreeWidget *treeWidget;
};

XbelWriter Class Implementation

The XbelWriter constructor accepts a treeWidget to initialize within its definition. We enable
QXmlStreamWriter's auto-formatting property to ensure line-breaks and indentations are added automatically to empty sections between elements, increasing readability as the data is split into several lines.

The following code example is written in c++.
XbelWriter::XbelWriter(QTreeWidget *treeWidget)
    : treeWidget(treeWidget)
{
    setAutoFormatting(true);
}
The writeFile() function accepts a QIODevice object and sets it using setDevice(). This function then writes the document type definition(DTD), the start element, the version, and treeWidget's top-level items.

The following code example is written in c++.
bool XbelWriter::writeFile(QIODevice *device)
{
    setDevice(device);

    writeStartDocument();
    writeDTD("<!DOCTYPE xbel>");
    writeStartElement("xbel");
    writeAttribute("version", "1.0");
    for (int i = 0; i < treeWidget->topLevelItemCount(); ++i)
        writeItem(treeWidget->topLevelItem(i));

    writeEndDocument();
    return true;
}
The writeItem() function accepts a QTreeWidget object and writes it to the stream, depending on its tagName, which can either be a "folder", "bookmark", or "separator".

The following code example is written in c++.
void XbelWriter::writeItem(QTreeWidgetItem *item)
{
    QString tagName = item->data(0, Qt::UserRole).toString();
    if (tagName == "folder") {
        bool folded = !treeWidget->isItemExpanded(item);
        writeStartElement(tagName);
        writeAttribute("folded", folded ? "yes" : "no");
        writeTextElement("title", item->text(0));
        for (int i = 0; i < item->childCount(); ++i)
            writeItem(item->child(i));
        writeEndElement();
    } else if (tagName == "bookmark") {
        writeStartElement(tagName);
        if (!item->text(1).isEmpty())
            writeAttribute("href", item->text(1));
        writeTextElement("title", item->text(0));
        writeEndElement();
    } else if (tagName == "separator") {
        writeEmptyElement(tagName);
    }
}

XbelReader Class Definition

The XbelReader class is a subclass of
QXmlStreamReader, the pendent class for QXmlStreamWriter. XbelReader contains a private instance of QTreeWidget to group bookmarks according to their hierarchies.
class XbelReader : public QXmlStreamReader
{
public:

    XbelReader(QTreeWidget *treeWidget);


    bool read(QIODevice *device);

private:

    void readUnknownElement();
    void readXBEL();
    void readTitle(QTreeWidgetItem *item);
    void readSeparator(QTreeWidgetItem *item);
    void readFolder(QTreeWidgetItem *item);
    void readBookmark(QTreeWidgetItem *item);

    QTreeWidgetItem *createChildItem(QTreeWidgetItem *item);

    QTreeWidget *treeWidget;


    QIcon folderIcon;
    QIcon bookmarkIcon;
};

XbelReader Class Implementation

The XbelReader constructor accepts a
QTreeWidget to initialize the treeWidget within its definition. A QStyle object is used to set treeWidget's style property. The folderIcon is set to QIcon::Normal mode where the pixmap is only displayed when the user is not interacting with the icon. The QStyle::SP_DirClosedIcon, QStyle::SP_DirOpenIcon, and QStyle::SP_FileIcon correspond to standard pixmaps that follow the style of your GUI.

The following code example is written in c++.
XbelReader::XbelReader(QTreeWidget *treeWidget)
    : treeWidget(treeWidget)
{
    QStyle *style = treeWidget->style();

    folderIcon.addPixmap(style->standardPixmap(QStyle::SP_DirClosedIcon),
                         QIcon::Normal, QIcon::Off);
    folderIcon.addPixmap(style->standardPixmap(QStyle::SP_DirOpenIcon),
                         QIcon::Normal, QIcon::On);
    bookmarkIcon.addPixmap(style->standardPixmap(QStyle::SP_FileIcon));
}
The read() function accepts a QIODevice and sets it using setDevice(). The actual process of reading only takes place in event the file is a valid XBEL 1.0 file. Otherwise, the raiseError() function is used to display an error message.

The following code example is written in c++.
bool XbelReader::read(QIODevice *device)
{
    setDevice(device);

    while (!atEnd()) {
        readNext();

        if (isStartElement()) {
            if (name() == "xbel" && attributes().value("version") == "1.0")
                readXBEL();
            else
                raiseError(QObject::tr("The file is not an XBEL version 1.0 file."));
        }
    }

    return !error();
}
The readUnknownElement() function reads an unknown element. The Q_ASSERT() macro is used to provide a pre-condition for the function.

The following code example is written in c++.
void XbelReader::readUnknownElement()
{
    Q_ASSERT(isStartElement());

    while (!atEnd()) {
        readNext();

        if (isEndElement())
            break;

        if (isStartElement())
            readUnknownElement();
    }
}
The readXBEL() function reads the name of a startElement and calls the appropriate function to read it, depending on whether if its a "folder", "bookmark" or "separator". Otherwise, it calls readUnknownElement().

The following code example is written in c++.
void XbelReader::readXBEL()
{
    Q_ASSERT(isStartElement() && name() == "xbel");

    while (!atEnd()) {
        readNext();

        if (isEndElement())
            break;

        if (isStartElement()) {
            if (name() == "folder")
                readFolder(0);
            else if (name() == "bookmark")
                readBookmark(0);
            else if (name() == "separator")
                readSeparator(0);
            else
                readUnknownElement();
        }
    }
}
The readTitle() function reads the bookmark's title.

The following code example is written in c++.
void XbelReader::readTitle(QTreeWidgetItem *item)
{
    Q_ASSERT(isStartElement() && name() == "title");

    QString title = readElementText();
    item->setText(0, title);
}
The readSeparator() function creates a separator and sets its flags. The text is set to 30 "0xB7", the HEX equivalent for period, and then read using readElementText().

The following code example is written in c++.
void XbelReader::readSeparator(QTreeWidgetItem *item)
{
    QTreeWidgetItem *separator = createChildItem(item);
    separator->setFlags(item->flags() & ~Qt::ItemIsSelectable);
    separator->setText(0, QString(30, 0xB7));
    readElementText();
}

MainWindow Class Definition

The MainWindow class is a subclass of
QMainWindow, with a File menu and a Help menu.
class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow();

public slots:
    void open();
    void saveAs();
    void about();

private:
    void createActions();
    void createMenus();

    QTreeWidget *treeWidget;

    QMenu *fileMenu;
    QMenu *helpMenu;
    QAction *openAct;
    QAction *saveAsAct;
    QAction *exitAct;
    QAction *aboutAct;
    QAction *aboutQtAct;
};

MainWindow Class Implementation

The MainWindow constructor instantiates the
QTreeWidget object, treeWidget and sets its header with a QStringList object, labels. The constructor also invokes createActions() and createMenus() to set up the menus and their corresponding actions. The statusBar() is used to display the message "Ready" and the window's size is fixed to 480x320 pixels.

The following code example is written in c++.
MainWindow::MainWindow()
{
    QStringList labels;
    labels << tr("Title") << tr("Location");

    treeWidget = new QTreeWidget;
    treeWidget->header()->setResizeMode(QHeaderView::Stretch);
    treeWidget->setHeaderLabels(labels);
    setCentralWidget(treeWidget);

    createActions();
    createMenus();

    statusBar()->showMessage(tr("Ready"));

    setWindowTitle(tr("QXmlStream Bookmarks"));
    resize(480, 320);
}
The open() function enables the user to open an XBEL file using QFileDialog::getOpenFileName(). A warning message is displayed along with the fileName and errorString if the file cannot be read or if there is a parse error.

The following code example is written in c++.
void MainWindow::open()
{
    QString fileName =
            QFileDialog::getOpenFileName(this, tr("Open Bookmark File"),
                                         QDir::currentPath(),
                                         tr("XBEL Files (*.xbel *.xml)"));
    if (fileName.isEmpty())
        return;

    treeWidget->clear();


    QFile file(fileName);
    if (!file.open(QFile::ReadOnly | QFile::Text)) {
        QMessageBox::warning(this, tr("QXmlStream Bookmarks"),
                             tr("Cannot read file %1:\n%2.")
                             .arg(fileName)
                             .arg(file.errorString()));
        return;
    }

    XbelReader reader(treeWidget);
    if (!reader.read(&file)) {
        QMessageBox::warning(this, tr("QXmlStream Bookmarks"),
                             tr("Parse error in file %1 at line %2, column %3:\n%4")
                             .arg(fileName)
                             .arg(reader.lineNumber())
                             .arg(reader.columnNumber())
                             .arg(reader.errorString()));
    } else {
        statusBar()->showMessage(tr("File loaded"), 2000);
    }

}
The saveAs() function displays a QFileDialog, prompting the user for a fileName using QFileDialog::getSaveFileName(). Similar to the open() function, this function also displays a warning message if the file cannot be written to.

The following code example is written in c++.
void MainWindow::saveAs()
{
    QString fileName =
            QFileDialog::getSaveFileName(this, tr("Save Bookmark File"),
                                         QDir::currentPath(),
                                         tr("XBEL Files (*.xbel *.xml)"));
    if (fileName.isEmpty())
        return;

    QFile file(fileName);
    if (!file.open(QFile::WriteOnly | QFile::Text)) {
        QMessageBox::warning(this, tr("QXmlStream Bookmarks"),
                             tr("Cannot write file %1:\n%2.")
                             .arg(fileName)
                             .arg(file.errorString()));
        return;
    }

    XbelWriter writer(treeWidget);
    if (writer.writeFile(&file))
        statusBar()->showMessage(tr("File saved"), 2000);
}
The about() function displays a QMessageBox with a brief description of the example.

The following code example is written in c++.
void MainWindow::about()
{
   QMessageBox::about(this, tr("About QXmlStream Bookmarks"),
            tr("The <b>QXmlStream Bookmarks</b> example demonstrates how to use Qt's "
               "QXmlStream classes to read and write XML documents."));
}
In order to implement the open(), saveAs(), exit(), about() and aboutQt() functions, we connect them to QAction objects and add them to the fileMenu and helpMenu. The connections are as shown below:

The following code example is written in c++.
void MainWindow::createActions()
{
    openAct = new QAction(tr("&Open..."), this);
    openAct->setShortcut(tr("Ctrl+O"));
    connect(openAct, SIGNAL(triggered()), this, SLOT(open()));

    saveAsAct = new QAction(tr("&Save As..."), this);
    saveAsAct->setShortcut(tr("Ctrl+S"));
    connect(saveAsAct, SIGNAL(triggered()), this, SLOT(saveAs()));

    exitAct = new QAction(tr("E&xit"), this);
    exitAct->setShortcut(tr("Ctrl+Q"));
    connect(exitAct, SIGNAL(triggered()), this, SLOT(close()));

    aboutAct = new QAction(tr("&About"), this);
    connect(aboutAct, SIGNAL(triggered()), this, SLOT(about()));

    aboutQtAct = new QAction(tr("About &Qt"), this);
    connect(aboutQtAct, SIGNAL(triggered()), qApp, SLOT(aboutQt()));
}
The createMenus() function creates the fileMenu and helpMenu and adds the QAction objects to them in order to create the menu shown in the screenshot below:






The following code example is written in c++.
void MainWindow::createMenus()
{
    fileMenu = menuBar()->addMenu(tr("&File"));
    fileMenu->addAction(openAct);
    fileMenu->addAction(saveAsAct);
    fileMenu->addAction(exitAct);

    menuBar()->addSeparator();

    helpMenu = menuBar()->addMenu(tr("&Help"));
    helpMenu->addAction(aboutAct);
    helpMenu->addAction(aboutQtAct);
}

main() Function

main() The main() function instantiates MainWindow and invokes the show() function.

The following code example is written in c++.
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MainWindow mainWin;
    mainWin.show();
    mainWin.open();
    return app.exec();
}
See the XML Bookmark Exchange Language Resource Page for more information about XBEL files.


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Qt Jambi 4.5.2_01