C++/Qt/QPlainTextEdit

Code editor

<source lang="cpp"> /****************************************************************************

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1. ifndef CODEEDITOR_H
2. define CODEEDITOR_H
3. include <QPlainTextEdit>
4. include <QObject>

QT_BEGIN_NAMESPACE class QPaintEvent; class QResizeEvent; class QSize; class QWidget; QT_END_NAMESPACE class LineNumberArea; //![codeeditordefinition] class CodeEditor : public QPlainTextEdit {

   Q_OBJECT

public:

   CodeEditor(QWidget *parent = 0);
   void lineNumberAreaPaintEvent(QPaintEvent *event);
   int lineNumberAreaWidth();

protected:

   void resizeEvent(QResizeEvent *event);

private slots:

   void updateLineNumberAreaWidth(int newBlockCount);
   void highlightCurrentLine();
   void updateLineNumberArea(const QRect &, int);

private:

   QWidget *lineNumberArea;

}; //![codeeditordefinition] //![extraarea] class LineNumberArea : public QWidget { public:

   LineNumberArea(CodeEditor *editor) : QWidget(editor) {
       codeEditor = editor;
   }
   QSize sizeHint() const {
       return QSize(codeEditor->lineNumberAreaWidth(), 0);
   }

protected:

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

private:

   CodeEditor *codeEditor;

}; //![extraarea]

1. endif

1. include <QtGui>
2. include "codeeditor.h"

//![constructor] CodeEditor::CodeEditor(QWidget *parent) : QPlainTextEdit(parent) {

   lineNumberArea = new LineNumberArea(this);
   connect(this, SIGNAL(blockCountChanged(int)), this, SLOT(updateLineNumberAreaWidth(int)));
   connect(this, SIGNAL(updateRequest(const QRect &, int)), this, SLOT(updateLineNumberArea(const QRect &, int)));
   connect(this, SIGNAL(cursorPositionChanged()), this, SLOT(highlightCurrentLine()));
   updateLineNumberAreaWidth(0);
   highlightCurrentLine();

} //![constructor] //![extraAreaWidth] int CodeEditor::lineNumberAreaWidth() {

   int digits = 1;
   int max = qMax(1, blockCount());
   while (max >= 10) {
       max /= 10;
       ++digits;
   }
   int space = 3 + fontMetrics().width(QLatin1Char("9")) * digits;
   return space;

} //![extraAreaWidth] //![slotUpdateExtraAreaWidth] void CodeEditor::updateLineNumberAreaWidth(int /* newBlockCount */) {

   setViewportMargins(lineNumberAreaWidth(), 0, 0, 0);

} //![slotUpdateExtraAreaWidth] //![slotUpdateRequest] 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);

} //![slotUpdateRequest] //![resizeEvent] void CodeEditor::resizeEvent(QResizeEvent *e) {

   QPlainTextEdit::resizeEvent(e);
   QRect cr = contentsRect();
   lineNumberArea->setGeometry(QRect(cr.left(), cr.top(), lineNumberAreaWidth(), cr.height()));

} //![resizeEvent] //![cursorPositionChanged] 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);

} //![cursorPositionChanged] //![extraAreaPaintEvent_0] void CodeEditor::lineNumberAreaPaintEvent(QPaintEvent *event) {

   QPainter painter(lineNumberArea);
   painter.fillRect(event->rect(), Qt::lightGray);

//![extraAreaPaintEvent_0] //![extraAreaPaintEvent_1]

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

//![extraAreaPaintEvent_1] //![extraAreaPaintEvent_2]

   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;
   }

} //![extraAreaPaintEvent_2]

1. include <QtGui>
2. include "codeeditor.h"

int main(int argv, char **args) {

   QApplication app(argv, args);
   CodeEditor editor;
   editor.setWindowTitle(QObject::tr("Code Editor Example"));
   editor.show();
   return app.exec();

}

 </source>