在qt5中如何设置plantextedit每行只显示三个字符后换行

您可以通过继承 QPlainTextEdit 类并重载其 paintEvent() 方法实现该功能。具体步骤如下：

1. 在自定义的 QPlainTextEdit 类中定义行宽和行高：

class MyPlainTextEdit : public QPlainTextEdit
{
public:
    MyPlainTextEdit(QWidget *parent = nullptr);

protected:
    void paintEvent(QPaintEvent *event) override;

private:
    int m_lineWidth;
    int m_lineHeight;
};

2. 在构造函数中初始化行宽和行高：

MyPlainTextEdit::MyPlainTextEdit(QWidget *parent)
    : QPlainTextEdit(parent)
{
    QFontMetrics metrics(font());
    m_lineWidth = metrics.width("A") * 3; // 每行只显示三个字符
    m_lineHeight = metrics.lineSpacing();
}

3. 重载 paintEvent() 方法，在其中按照行宽和行高进行绘制：

void MyPlainTextEdit::paintEvent(QPaintEvent *event)
{
    QPainter painter(viewport());
    painter.setFont(font());
    painter.setPen(palette().color(QPalette::Text));

    QRect rect = event->rect();
    int firstBlock = blockAt(rect.topLeft());
    int lastBlock = blockAt(rect.bottomRight());
    int blockCount = document()->blockCount();

    for (int i = firstBlock; i <= lastBlock && i < blockCount; ++i) {
        QTextBlock block = document()->findBlockByNumber(i);

        if (block.isValid()) {
            QRectF blockRect = blockBoundingRect(block);
            int blockTop = blockRect.top();
            int blockHeight = blockRect.height();
            int lineNumber = block.blockNumber() + 1;
            QString lineText = QString::number(lineNumber);
            int lineWidth = m_lineWidth;

            if (lineWidth > blockRect.width()) {
                lineWidth = blockRect.width();
            }

            if (lineWidth > 0 && lineNumber % 2 == 1) {
                painter.drawText(QRect(0, blockTop, lineWidth, blockHeight), Qt::AlignRight | Qt::AlignVCenter, lineText);
            }

            int x = lineWidth;
            int y = blockTop;

            QTextLayout layout(block.text(), font());
            layout.beginLayout();
            while (true) {
                QTextLine line = layout.createLine();
                if (!line.isValid()) {
                    break;
                }

                line.setLineWidth(lineWidth);
                line.setPosition(QPointF(x, y));
                y += m_lineHeight;

                painter.drawText(line.position(), line.text());
            }
            layout.endLayout();
        }
    }
}

这样，您就可以在 QPlainTextEdit 中实现每行只显示三个字符后换行的效果了。