如何获取放置在图形场景中的对象的放置事件？

Question

我有图形视图（QGraphics 视图）设置场景（QGraphic 场景）我正在场景中放置对象它工作正常，我必须通过从参数列表中拖动参数来为放置的对象分配参数。我已经实现了拖放事件object.but 当我从 object.how 上的参数列表非接受符号中拖动参数以通过拖放将参数分配给对象时？欢迎任何其他建议和示例，我可以从中获得实施的想法。

gui 图像

speedometer.cpp

#include <QMimeData>   

SpeedoMeter::SpeedoMeter( QWidget *parent ):
    QwtDial( parent ),
    d_label( "km/h" )   
{

    setAcceptDrops(true);

}

void SpeedoMeter::dragEnterEvent(QDragEnterEvent *event)   
{    

    if (event->mimeData()->hasFormat(paramlistMimeType()))
    {
    qDebug()<<"dragenter event in speedo" ;
    event->accept();
    }

}

void SpeedoMeter::dragMoveEvent(QDragMoveEvent *event)
{

    if (event->mimeData()->hasFormat(paramlistMimeType()))
    {
    qDebug()<<"dragmove event in speedo" ; 
    event->acceptProposedAction();
    }

}

void SpeedoMeter::dropEvent(QDropEvent *event)
{

    if (event->mimeData()->hasFormat(paramlistMimeType()))
    {
     qDebug()<<"dragmove event in speedo" ;   
      event->accept();   
    }

}

Answer 1

以下示例显示了如何实现接受拖放的逻辑：

speedometer.h

#ifndef SPEEDOMETER_H
#define SPEEDOMETER_H

#include <qwt_dial.h>

class SpeedoMeter : public QwtDial
{
public:
    SpeedoMeter(QWidget *parent=nullptr);

protected:
    void dragEnterEvent(QDragEnterEvent *event);
    void dropEvent(QDropEvent *event);
    void dragMoveEvent(QDragMoveEvent *event);
    void paintEvent(QPaintEvent *event);
private:
    QString d_label;
};


#endif // SPEEDOMETER_H

speedometer.cpp

#include "speedometer.h"

#include <qwt_dial_needle.h>

#include <QDragEnterEvent>
#include <QMimeData>
#include <QPainter>

SpeedoMeter::SpeedoMeter(QWidget *parent):
    QwtDial(parent),
    d_label( "km/h" )
{
    setAcceptDrops(true);
    QwtDialSimpleNeedle *nd = new QwtDialSimpleNeedle(QwtDialSimpleNeedle::Arrow, Qt::white, Qt::red);
    setNeedle(nd);
    setValue(80);
}

void SpeedoMeter::dragEnterEvent(QDragEnterEvent *event)
{
    if(event->mimeData()->hasFormat("application/x-qabstractitemmodeldatalist"))
        event->acceptProposedAction();
}

void SpeedoMeter::dropEvent(QDropEvent *event)
{
    const QMimeData *mimedata = event->mimeData();

    if(mimedata->hasFormat("application/x-qabstractitemmodeldatalist")){
        QString text;
        // 
        QByteArray encoded = mimedata->data("application/x-qabstractitemmodeldatalist");
        QDataStream stream(&encoded, QIODevice::ReadOnly);
        while (!stream.atEnd()) {
            int row, col;
            QMap<int,  QVariant> roleDataMap;
            stream >> row >> col >> roleDataMap;
            if(roleDataMap.contains(Qt::DisplayRole)){
                text = roleDataMap[Qt::DisplayRole].toString();
                break;
            }
        }
        // your text
        d_label = text;
        update();
    }
}

void SpeedoMeter::dragMoveEvent(QDragMoveEvent *event)
{
    if(event->mimeData()->hasFormat("application/x-qabstractitemmodeldatalist"))
        event->accept();
}

void SpeedoMeter::paintEvent(QPaintEvent *event)
{
    // 
    QwtDial::paintEvent(event);
    QPainter painter(this);
    painter.setPen(Qt::black);
    QFont font;
    font.setPointSize(11);
    painter.setFont(font);
    QString text = QString("%1 %2").arg(value()).arg(d_label);
    QPoint c = rect().center();
    QSize Size = painter.fontMetrics().size(Qt::TextSingleLine, text);
    painter.drawText(QPointF(c.x() -Size.width()/2, c.y() + 2.5*Size.height()), text);

}

main.cpp

#include "speedometer.h"

#include <QApplication>
#include <QGraphicsView>
#include <QHBoxLayout>
#include <QListWidget>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QWidget w;
    QHBoxLayout *layout = new QHBoxLayout(&w);
    QListWidget listWidget;
    listWidget.setDragDropMode(QAbstractItemView::DragOnly);
    listWidget.addItems({"km/h", "ft/s", "m/s", "miles/h"});

    QGraphicsView view;
    QGraphicsScene scene;
    view.setScene(&scene);

    SpeedoMeter speed;
    scene.addWidget(&speed);
    layout->addWidget(&listWidget);
    layout->addWidget(&view);
    w.show();

    return a.exec();
}

在下面link你可以找到完整的例子。

如何获取放置在图形场景中的对象的放置事件？

how to get drop events of object which is placed in graphic scene?

qt

drag-and-drop

qwidget

qgraphicsscene