codeeditor.cpp Example File

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  #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().width(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;
      }
  }