用Qt的GraphicsItem 自绘一个QLinedit 并且可以输入文本

以下是一个用Qt的GraphicsItem自绘的QLinedit并且可以输入文本的示例代码：

#include <QGraphicsItem>
#include <QPainter>
#include <QLineEdit>

class CustomLineEdit : public QGraphicsItem
{
public:
    CustomLineEdit(QGraphicsItem *parent = nullptr)
        : QGraphicsItem(parent)
    {
        setFlag(ItemIsFocusable);
        setAcceptHoverEvents(true);
        m_edit = new QLineEdit();
        m_edit->setFrame(false);
        m_edit->setAttribute(Qt::WA_TranslucentBackground);
        m_edit->setStyleSheet("QLineEdit { background-color: transparent; }");
        m_edit->setAlignment(Qt::AlignCenter);
    }

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget = nullptr) override
    {
        Q_UNUSED(option);
        Q_UNUSED(widget);

        QRectF rect = boundingRect();
        painter->setPen(Qt::NoPen);
        painter->setBrush(Qt::white);
        painter->drawRect(rect);

        painter->setPen(Qt::black);
        painter->drawText(rect, Qt::AlignCenter, m_edit->text());
    }

    QRectF boundingRect() const override
    {
        return QRectF(0, 0, 100, 20);
    }

    void keyPressEvent(QKeyEvent *event) override
    {
        if (event->key() == Qt::Key_Backspace)
        {
            QString text = m_edit->text();
            if (!text.isEmpty())
            {
                text.chop(1);
                m_edit->setText(text);
                update();
            }
        }
        else
        {
            m_edit->keyPressEvent(event);
            update();
        }
    }

    void focusInEvent(QFocusEvent *event) override
    {
        m_edit->setFocus();
        update();
    }

    void focusOutEvent(QFocusEvent *event) override
    {
        m_edit->clearFocus();
        update();
    }

    void hoverEnterEvent(QGraphicsSceneHoverEvent *event) override
    {
        setCursor(Qt::IBeamCursor);
        update();
    }

    void hoverLeaveEvent(QGraphicsSceneHoverEvent *event) override
    {
        unsetCursor();
        update();
    }

private:
    QLineEdit *m_edit;
};

这里我们定义了一个CustomLineEdit类，继承自QGraphicsItem，然后在paint()函数中绘制了一个白色的矩形和黑色的文本，文本内容是从QLineEdit中获取的。在keyPressEvent()函数中，我们监听了键盘事件，如果是退格键，则从QLineEdit中删除最后一个字符，如果是其他键，则将事件传递给QLineEdit处理。在focusInEvent()和focusOutEvent()函数中，我们将焦点转移到QLineEdit上，以便能够输入文本。在hoverEnterEvent()和hoverLeaveEvent()函数中，我们设置了鼠标悬停时的光标形状。