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

Question

i have graphic view(QGraphics view) setted scene(QGraphic scene) i am dropping objects on scene its working fine, i have to assign parameter for dropped object by dragging parameter from parameter list .i have implemented drag drop events of object.but when i am dragging parameter from param list non- acceptance symbol on object.how to assign param to object by dropping ? Any other suggestions and examples are welcome where i can get ideas to implementation.
image of gui
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

The following example shows how to implement the logic to accept the drag-and-drop:
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;
// https://stackoverflow.com/questions/1723989/how-to-decode-application-x-qabstractitemmodeldatalist-in-qt-for-drag-and-drop
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)
{
// https://stackoverflow.com/questions/43904204/qwt-dial-show-unit
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();
}
In the following link you can find the complete example.