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# codeeditor.cpp Example File

widgets/codeeditor/codeeditor.cpp

     /****************************************************************************
     **
     ** Copyright (C) 2015 The Qt Company Ltd.
     ** Contact: http://www.qt.io/licensing/
     **
     ** This file is part of the examples of the Qt Toolkit.
     **
     ** $QT_BEGIN_LICENSE:BSD$
     ** You may use this file under the terms of the BSD license as follows:
     **
     ** "Redistribution and use in source and binary forms, with or without
     ** modification, are permitted provided that the following conditions are
     ** met:
     **   * Redistributions of source code must retain the above copyright
     **     notice, this list of conditions and the following disclaimer.
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     **     notice, this list of conditions and the following disclaimer in
     **     the documentation and/or other materials provided with the
     **     distribution.
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     **     contributors may be used to endorse or promote products derived
     **     from this software without specific prior written permission.
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     ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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     #include <QtGui>

     #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;
         }
     }