C++ QToolButton点击后出现在QtDraawingPaperEditor中出现可以随着鼠标移动的图片，点击左键后，图片被放下

您可以通过以下步骤实现：

1. 创建一个QGraphicsScene对象和一个QGraphicsPixmapItem对象。将QGraphicsPixmapItem对象添加到QGraphicsScene对象中。

2. 在QToolButton的clicked()信号中，显示一个QFileDialog来选择要放置的图像文件。将所选文件加载到QPixmap对象中。

3. 将QPixmap对象设置为QGraphicsPixmapItem对象的pixmap，并根据需要调整其大小。

4. 在QGraphicsScene对象中添加该QGraphicsPixmapItem对象。

5. 在QGraphicsScene对象上设置一个捕捉鼠标事件的事件过滤器。

6. 在事件过滤器中，捕捉鼠标按下和释放事件。在鼠标按下时，将QGraphicsPixmapItem对象从QGraphicsScene对象中移除，并将其添加到QGraphicsView对象中。然后，在QGraphicsView对象上设置一个捕捉鼠标事件的事件过滤器。

7. 在QGraphicsView对象的事件过滤器中，捕捉鼠标释放事件。在鼠标释放时，将QGraphicsPixmapItem对象移动到QGraphicsScene对象中，并将其位置设置为鼠标释放的位置。

下面是一个示例代码，演示如何实现上述步骤：

#include <QtWidgets>

class DrawingPaperEditor : public QGraphicsView
{
public:
    DrawingPaperEditor(QWidget *parent = nullptr);

protected:
    bool eventFilter(QObject *obj, QEvent *event) override;

private:
    QGraphicsScene *m_scene;
    QGraphicsPixmapItem *m_pixmapItem;
    QPixmap m_pixmap;
};

DrawingPaperEditor::DrawingPaperEditor(QWidget *parent)
    : QGraphicsView(parent)
    , m_scene(new QGraphicsScene(this))
    , m_pixmapItem(new QGraphicsPixmapItem)
{
    setScene(m_scene);
    m_scene->addItem(m_pixmapItem);

    // Install event filter on the scene to capture mouse press events.
    m_scene->installEventFilter(this);
}

bool DrawingPaperEditor::eventFilter(QObject *obj, QEvent *event)
{
    if (obj == m_scene) {
        if (event->type() == QEvent::GraphicsSceneMousePress) {
            QMouseEvent *mouseEvent = static_cast<QMouseEvent *>(event);
            if (mouseEvent->button() == Qt::LeftButton) {
                // Remove pixmap item from scene and add it to view.
                m_scene->removeItem(m_pixmapItem);
                QGraphicsView *view = qobject_cast<QGraphicsView *>(parent());
                if (view) {
                    view->scene()->addItem(m_pixmapItem);
                    view->installEventFilter(this);
                }
            }
        } else if (event->type() == QEvent::GraphicsSceneMouseRelease) {
            QMouseEvent *mouseEvent = static_cast<QMouseEvent *>(event);
            if (mouseEvent->button() == Qt::LeftButton) {
                // Move pixmap item to scene and set its position to mouse release position.
                QGraphicsView *view = qobject_cast<QGraphicsView *>(parent());
                if (view) {
                    QPointF pos = view->mapToScene(mouseEvent->pos());
                    m_pixmapItem->setPos(pos);
                    view->scene()->removeItem(m_pixmapItem);
                    m_scene->addItem(m_pixmapItem);
                    view->removeEventFilter(this);
                }
            }
        }
    } else if (obj == parent()) {
        if (event->type() == QEvent::MouseButtonRelease) {
            QGraphicsView *view = qobject_cast<QGraphicsView *>(parent());
            if (view) {
                QPointF pos = view->mapToScene(static_cast<QMouseEvent *>(event)->pos());
                m_pixmapItem->setPos(pos);
            }
        }
    }

    return false;
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QToolButton toolButton;
    toolButton.setText("Add Image");
    DrawingPaperEditor editor;
    QVBoxLayout layout;
    layout.addWidget(&toolButton);
    layout.addWidget(&editor);
    QWidget widget;
    widget.setLayout(&layout);
    widget.show();

    QObject::connect(&toolButton, &QToolButton::clicked, [&](){
        QString fileName = QFileDialog::getOpenFileName(&widget, "Open Image", QString(), "Images (*.png *.xpm *.jpg)");
        if (!fileName.isEmpty()) {
            QPixmap pixmap(fileName);
            if (!pixmap.isNull()) {
                editor.setSceneRect(pixmap.rect());
                editor.m_pixmap = pixmap;
                editor.m_pixmapItem->setPixmap(pixmap.scaled(editor.width(), editor.height(), Qt::KeepAspectRatio));
                editor.m_pixmapItem->setPos(editor.sceneRect().center());
            }
        }
    });

    return a.exec();
}