QT实现代码编辑器

#include <QtWidgets>
#include "codeeditor.h"

CodeEditor::CodeEditor(QWidget *parent) : QPlainTextEdit(parent)
{
lineNumberArea = new LineNumberArea(this);

connect(this, SIGNAL(blockCountChanged(int)), this, SLOT(updateLineNumberAreaWidth(int)));
connect(this, SIGNAL(updateRequest(QRect,int)), this, SLOT(updateLineNumberArea(QRect,int)));
connect(this, SIGNAL(cursorPositionChanged()), this, SLOT(highlightCurrentLine()));

updateLineNumberAreaWidth(0);
highlightCurrentLine();
}

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

int space = 3 + fontMetrics().horizontalAdvance(QLatin1Char('9')) * digits;

return space;
}



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


void CodeEditor::updateLineNumberArea(const QRect &rect, int dy)
{
if (dy)
lineNumberArea->scroll(0, dy);
else
lineNumberArea->update(0, rect.y(), lineNumberArea->width(), rect.height());

if (rect.contains(viewport()->rect()))
updateLineNumberAreaWidth(0);
}


void CodeEditor::resizeEvent(QResizeEvent *e)
{
QPlainTextEdit::resizeEvent(e);

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


void CodeEditor::highlightCurrentLine()
{
QList<QTextEdit::ExtraSelection> extraSelections;

if (!isReadOnly()) {
QTextEdit::ExtraSelection selection;

QColor lineColor = QColor(Qt::yellow).lighter(160);

selection.format.setBackground(lineColor);
selection.format.setProperty(QTextFormat::FullWidthSelection, true);
selection.cursor = textCursor();
selection.cursor.clearSelection();
extraSelections.append(selection);
    }

setExtraSelections(extraSelections);
}



void CodeEditor::lineNumberAreaPaintEvent(QPaintEvent *event)
{
QPainter painter(lineNumberArea);
painter.fillRect(event->rect(), Qt::lightGray);


QTextBlock block = firstVisibleBlock();
int blockNumber = block.blockNumber();
int top = (int) blockBoundingGeometry(block).translated(contentOffset()).top();
int bottom = top + (int) blockBoundingRect(block).height();

while (block.isValid() && top <= event->rect().bottom()) {
if (block.isVisible() && bottom >= event->rect().top()) {
QString number = QString::number(blockNumber + 1);
painter.setPen(Qt::black);
painter.drawText(0, top, lineNumberArea->width(), fontMetrics().height(),
Qt::AlignRight, number);
        }

block = block.next();
top = bottom;
bottom = top + (int) blockBoundingRect(block).height();
++blockNumber;
    }
}