问如何向QTextEdit中添加行号？

EN

class LineNumberArea : public QWidget
{
    Q_OBJECT

public:
    LineNumberArea(QTextEdit *editor);

    QSize sizeHint() const;

protected:
    void paintEvent(QPaintEvent *event);

private:
    QTextEdit *codeEditor;
};

LineNumberArea::LineNumberArea(QTextEdit *editor) : QWidget(editor) {
    codeEditor = editor;
}

QSize LineNumberArea::sizeHint() const {
    return QSize(((QTextEditHighlighter *)codeEditor)->lineNumberAreaWidth(), 0);
}

void LineNumberArea::paintEvent(QPaintEvent *event) {
    ((QTextEditHighlighter *)codeEditor)->lineNumberAreaPaintEvent(event);
}

class QTextEditHighlighter : public QTextEdit
{
    Q_OBJECT

public:

    explicit QTextEditHighlighter(QWidget *parent = 0);

    int getFirstVisibleBlockId();
    void lineNumberAreaPaintEvent(QPaintEvent *event);
    int lineNumberAreaWidth();

signals:


public slots:

    void resizeEvent(QResizeEvent *e);

private slots:

    void updateLineNumberAreaWidth(int newBlockCount);
    void updateLineNumberArea(QRectF /*rect_f*/);
    void updateLineNumberArea(int /*slider_pos*/);
    void updateLineNumberArea();

private:

    QWidget *lineNumberArea;

};

#include "qtextedithighlighter.h"

QTextEditHighlighter::QTextEditHighlighter(QWidget *parent) :
    QTextEdit(parent)
{
    // Line numbers
    lineNumberArea = new LineNumberArea(this);
    ///
    connect(this->document(), SIGNAL(blockCountChanged(int)), this, SLOT(updateLineNumberAreaWidth(int)));
    connect(this->verticalScrollBar(), SIGNAL(valueChanged(int)), this, SLOT(updateLineNumberArea/*_2*/(int)));
    connect(this, SIGNAL(textChanged()), this, SLOT(updateLineNumberArea()));
    connect(this, SIGNAL(cursorPositionChanged()), this, SLOT(updateLineNumberArea()));
    ///
    updateLineNumberAreaWidth(0);
}

int QTextEditHighlighter::lineNumberAreaWidth()
{
    int digits = 1;
    int max = qMax(1, this->document()->blockCount());
    while (max >= 10) {
        max /= 10;
        ++digits;
    }

    int space = 13 +  fontMetrics().width(QLatin1Char('9')) * (digits);

    return space;
}

void QTextEditHighlighter::updateLineNumberAreaWidth(int /* newBlockCount */)
{
    setViewportMargins(lineNumberAreaWidth(), 0, 0, 0);
}


void QTextEditHighlighter::updateLineNumberArea(QRectF /*rect_f*/)
{
    QTextEditHighlighter::updateLineNumberArea();
}
void QTextEditHighlighter::updateLineNumberArea(int /*slider_pos*/)
{
    QTextEditHighlighter::updateLineNumberArea();
}
void QTextEditHighlighter::updateLineNumberArea()
{
    /*
     * When the signal is emitted, the sliderPosition has been adjusted according to the action,
     * but the value has not yet been propagated (meaning the valueChanged() signal was not yet emitted),
     * and the visual display has not been updated. In slots connected to this signal you can thus safely
     * adjust any action by calling setSliderPosition() yourself, based on both the action and the
     * slider's value.
     */
    // Make sure the sliderPosition triggers one last time the valueChanged() signal with the actual value !!!!
    this->verticalScrollBar()->setSliderPosition(this->verticalScrollBar()->sliderPosition());

    // Since "QTextEdit" does not have an "updateRequest(...)" signal, we chose
    // to grab the imformations from "sliderPosition()" and "contentsRect()".
    // See the necessary connections used (Class constructor implementation part).

    QRect rect =  this->contentsRect();
    lineNumberArea->update(0, rect.y(), lineNumberArea->width(), rect.height());
    updateLineNumberAreaWidth(0);
    //----------
    int dy = this->verticalScrollBar()->sliderPosition();
    if (dy > -1) {
        lineNumberArea->scroll(0, dy);
    }

    // Addjust slider to alway see the number of the currently being edited line...
    int first_block_id = getFirstVisibleBlockId();
    if (first_block_id == 0 || this->textCursor().block().blockNumber() == first_block_id-1)
        this->verticalScrollBar()->setSliderPosition(dy-this->document()->documentMargin());

//    // Snap to first line (TODO...)
//    if (first_block_id > 0)
//    {
//        int slider_pos = this->verticalScrollBar()->sliderPosition();
//        int prev_block_height = (int) this->document()->documentLayout()->blockBoundingRect(this->document()->findBlockByNumber(first_block_id-1)).height();
//        if (dy <= this->document()->documentMargin() + prev_block_height)
//            this->verticalScrollBar()->setSliderPosition(slider_pos - (this->document()->documentMargin() + prev_block_height));
//    }

}


void QTextEditHighlighter::resizeEvent(QResizeEvent *e)
{
    QTextEdit::resizeEvent(e);

    QRect cr = this->contentsRect();
    lineNumberArea->setGeometry(QRect(cr.left(), cr.top(), lineNumberAreaWidth(), cr.height()));
}


int QTextEditHighlighter::getFirstVisibleBlockId()
{
    // Detect the first block for which bounding rect - once translated 
    // in absolute coordinated - is contained by the editor's text area

    // Costly way of doing but since "blockBoundingGeometry(...)" doesn't 
    // exists for "QTextEdit"...

    QTextCursor curs = QTextCursor(this->document());
    curs.movePosition(QTextCursor::Start);
    for(int i=0; i < this->document()->blockCount(); ++i)
    {
        QTextBlock block = curs.block();

        QRect r1 = this->viewport()->geometry();
        QRect r2 = this->document()->documentLayout()->blockBoundingRect(block).translated(
                    this->viewport()->geometry().x(), this->viewport()->geometry().y() - (
                        this->verticalScrollBar()->sliderPosition()
                        ) ).toRect();

        if (r1.contains(r2, true)) { return i; }

        curs.movePosition(QTextCursor::NextBlock);
    }

    return 0;
}

void QTextEditHighlighter::lineNumberAreaPaintEvent(QPaintEvent *event)
{
    this->verticalScrollBar()->setSliderPosition(this->verticalScrollBar()->sliderPosition());

    QPainter painter(lineNumberArea);
    painter.fillRect(event->rect(), Qt::lightGray);
    int blockNumber = this->getFirstVisibleBlockId();

    QTextBlock block = this->document()->findBlockByNumber(blockNumber);
    QTextBlock prev_block = (blockNumber > 0) ? this->document()->findBlockByNumber(blockNumber-1) : block;
    int translate_y = (blockNumber > 0) ? -this->verticalScrollBar()->sliderPosition() : 0;

    int top = this->viewport()->geometry().top();

    // Adjust text position according to the previous "non entirely visible" block 
    // if applicable. Also takes in consideration the document's margin offset.
    int additional_margin;
    if (blockNumber == 0)
        // Simply adjust to document's margin
        additional_margin = (int) this->document()->documentMargin() -1 - this->verticalScrollBar()->sliderPosition();
    else
        // Getting the height of the visible part of the previous "non entirely visible" block
        additional_margin = (int) this->document()->documentLayout()->blockBoundingRect(prev_block)
                .translated(0, translate_y).intersect(this->viewport()->geometry()).height();

    // Shift the starting point
    top += additional_margin;

    int bottom = top + (int) this->document()->documentLayout()->blockBoundingRect(block).height();

    QColor col_1(90, 255, 30);      // Current line (custom green)
    QColor col_0(120, 120, 120);    // Other lines  (custom darkgrey)

    // Draw the numbers (displaying the current line number in green)
    while (block.isValid() && top <= event->rect().bottom()) {
        if (block.isVisible() && bottom >= event->rect().top()) {
            QString number = QString::number(blockNumber + 1);
            painter.setPen(QColor(120, 120, 120));
            painter.setPen((this->textCursor().blockNumber() == blockNumber) ? col_1 : col_0);
            painter.drawText(-5, top,
                             lineNumberArea->width(), fontMetrics().height(),
                             Qt::AlignRight, number);
        }

        block = block.next();
        top = bottom;
        bottom = top + (int) this->document()->documentLayout()->blockBoundingRect(block).height();
        ++blockNumber;
    }

}

// Here is the key to obtain the y coordinate of the block start
QTextCursor blockCursor(block);
QRect blockCursorRect = this->cursorRect(blockCursor);

painter.drawText(-5, blockCursorRect.y() /* + a little offset to align */,
                 m_lineNumberArea->width(), fixedLineHeight,
                 Qt::AlignRight, number);