Qt实例——代码编辑器

目录

概述

LineNumberArea

CodeEditor

参考

 

---

概述

窗体包含两个部分，左侧的行号显示区(LineNumberArea)和右侧的代码编辑区(CodeEditor)。其中CodeEditor为主窗体，继承自QPlainTextEdit；LineNumberArea为行号显示区，继承自QWidget。

LineNumberArea

class LineNumberArea : public QWidget
{
    public:
        LineNumberArea(CodeEditor *editor) : QWidget(editor) {
            codeEditor = editor;
        }
    
        //返回合适的窗体大小
        QSize sizeHint() const override {
            return QSize(codeEditor->lineNumberAreaWidth(), 0);
        }

    protected:
        //重写绘制函数，调用CodeEditor的方法
        void paintEvent(QPaintEvent *event) override {
            codeEditor->lineNumberAreaPaintEvent(event);
        }

    private:
        CodeEditor *codeEditor;
};

组合了CodeEditor类，构造时作为参数传入，控制行号窗体的大小及显示内容。

CodeEditor

class CodeEditor : public QPlainTextEdit
{
    Q_OBJECT

public:
    CodeEditor(QWidget *parent = nullptr);

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

protected:
    void resizeEvent(QResizeEvent *event) override;

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

private:
    QWidget *lineNumberArea;
};

CodeEditor::CodeEditor(QWidget *parent) : QPlainTextEdit(parent)
{
    lineNumberArea = new LineNumberArea(this);
    //每当按下回车或者删除回车(更新字符块),则newBlockCount计数,并触发该信号, newBlockCount 默认为1
    connect(this, &CodeEditor::blockCountChanged, this, &CodeEditor::updateLineNumberAreaWidth);
    connect(this, &CodeEditor::updateRequest, this, &CodeEditor::updateLineNumberArea);
    //光标改变时发出信号
    connect(this, &CodeEditor::cursorPositionChanged, this, &CodeEditor::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 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;
    }
}

参考

Code Editor Example：https://doc.qt.io/qt-5/qtwidgets-widgets-codeeditor-example.html

qt sizehint的理解：https://blog.csdn.net/sunxiaopengsun/article/details/83068292

窗口大小、位置及其大小改变引起的事件QResizeEvent：https://blog.csdn.net/humanking7/article/details/86108269

QPlainEdit编辑功能：https://www.cnblogs.com/lifexy/p/9003918.html