公有继承QObject和QGrapgicsPathItem后实现鼠标绘制直线图元c++完整代码

以下是实现鼠标绘制直线图元的完整代码：

#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsLineItem>
#include <QMouseEvent>

class LineItem : public QObject, public QGraphicsLineItem
{
    Q_OBJECT
public:
    LineItem(QGraphicsItem *parent = nullptr)
        : QObject(nullptr), QGraphicsLineItem(parent)
    {
        setPen(QPen(Qt::black, 2));
    }

protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *event) override
    {
        if (event->button() == Qt::LeftButton) {
            m_startPoint = event->scenePos();
            m_endPoint = m_startPoint;
            setLine(QLineF(m_startPoint, m_endPoint));
            setCursor(Qt::CrossCursor);
            event->accept();
        } else {
            event->ignore();
        }
    }

    void mouseMoveEvent(QGraphicsSceneMouseEvent *event) override
    {
        if (event->buttons() & Qt::LeftButton) {
            m_endPoint = event->scenePos();
            setLine(QLineF(m_startPoint, m_endPoint));
            event->accept();
        } else {
            event->ignore();
        }
    }

    void mouseReleaseEvent(QGraphicsSceneMouseEvent *event) override
    {
        if (event->button() == Qt::LeftButton) {
            setCursor(Qt::ArrowCursor);
            emit lineDrawn(QLineF(m_startPoint, m_endPoint));
            event->accept();
        } else {
            event->ignore();
        }
    }

signals:
    void lineDrawn(const QLineF &line);

private:
    QPointF m_startPoint;
    QPointF m_endPoint;
};

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QGraphicsScene scene;
    QGraphicsView view(&scene);
    view.setRenderHint(QPainter::Antialiasing);
    view.setDragMode(QGraphicsView::RubberBandDrag);

    QObject::connect(&scene, &QGraphicsScene::selectionChanged, [&]() {
        for (QGraphicsItem *item : scene.selectedItems()) {
            if (LineItem *lineItem = qgraphicsitem_cast<LineItem *>(item)) {
                qDebug() << "Selected line:" << lineItem->line();
            }
        }
    });

    QObject::connect(&scene, &QGraphicsScene::sceneRectChanged, [&]() {
        view.fitInView(scene.sceneRect(), Qt::KeepAspectRatio);
    });

    QObject::connect(&view, &QGraphicsView::dragEnterEvent, [&](QDragEnterEvent *event) {
        for (const QUrl &url : event->mimeData()->urls()) {
            if (url.isLocalFile()) {
                event->acceptProposedAction();
                return;
            }
        }
        event->ignore();
    });

    QObject::connect(&view, &QGraphicsView::dragMoveEvent, [&](QDragMoveEvent *event) {
        event->acceptProposedAction();
    });

    QObject::connect(&view, &QGraphicsView::dropEvent, [&](QDropEvent *event) {
        for (const QUrl &url : event->mimeData()->urls()) {
            if (url.isLocalFile()) {
                QGraphicsPixmapItem *pixmapItem = new QGraphicsPixmapItem(QPixmap(url.toLocalFile()));
                pixmapItem->setPos(event->scenePos());
                scene.addItem(pixmapItem);
            }
        }
        event->acceptProposedAction();
    });

    QObject::connect(&view, &QGraphicsView::doubleClicked, [&](QMouseEvent *event) {
        if (event->button() == Qt::LeftButton) {
            LineItem *lineItem = new LineItem(nullptr);
            scene.addItem(lineItem);

            QObject::connect(lineItem, &LineItem::lineDrawn, [&](const QLineF &line) {
                qDebug() << "New line:" << line;
            });

            lineItem->setPos(event->scenePos());
        }
    });

    view.show();
    return app.exec();
}

这个代码使用了Qt的图形界面框架，使用了QGraphicsScene、QGraphicsView、QGraphicsLineItem等类来实现。具体实现细节可以参考注释和Qt文档。