QGraphicsPixmapItem doesn't show in QGraphicsView - c++

Question

I subclassed QGraphicsView (class Display) and implemented drag and drop from a QTableView. The QGraphicsScene has in it preexisting items and the scene()->itemsBoundingRect covers the entire earth.
If I artificially set the QGraphicsPixmapItem's boundingRect to the viewPort() of the QGraphicsView, I don't see the QPixmap I set in the QGraphicsPixmapItem and added to the scene(). If I fitInView the scene()->itemsBoundingRect, the pixmap is dropped on the whole world. I would like it dropped on my viewport, but essentially fitInView viewPort doesn't show the item, even though according to debug it's visible and notObscured().
void Display::dragEnterEvent(QDragEnterEvent* event)
{
event->acceptProposedAction();
update();
}
void Display::dragMoveEvent(QDragMoveEvent* event){
event->acceptProposedAction();
update();
}
void TableView::mouseMoveEvent(QMouseEvent *event)
{
QDrag* drag = new QDrag(this);
QMimeData *mime = new QMimeData();
drag->setMimeData(mime);
QImage image("/Users/sb/Downloads/puffin.jpeg");
mime->setImageData(image);
drag->setPixmap(QPixmap::fromImage(image).scaled(10,10));
drag->exec();
QTableView::mouseMoveEvent(event);
}
Edited to try #Eyllanesc suggestion
void Display::dropEvent(QDropEvent* event)
{
setCacheMode(QGraphicsView::CacheBackground);
setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
if(event->mimeData()->hasImage())
{
pixMap = qvariant_cast<QPixmap>(event->mimeData()->imageData());
pixMap = pixMap.scaledToHeight(10);
pixMap = pixMap.scaledToWidth(10);
bool h = pixMap.isNull(); //returns false
posn = mapToScene(event->pos());
QRectF ff = mapToScene(viewport()->geometry()).boundingRect();
bool ps = ff.contains(posn); //returns true
item = new QGraphicsPixmapItem(pixMap);
scene()->addItem(item);
item->setPos( posn);
item->setZValue(100);
item->setVisible(true);
item->setOpacity(1.0);
item->update();
scene()->update();
auto lView = qobject_cast<QGraphicsView*>(this);
lView->fitInView(ff, Qt::KeepAspectRatio);// no pixmap is shown
invalidateScene(ff);
bool i = item->isObscured(); //returns false
repaint();
update();
}
event->acceptProposedAction();
}
-

Answer 1

In the next part I show you a working example of how to implement drag-and-drop from a QTableView to a QGraphicsView:
#include <QApplication>
#include <QDrag>
#include <QGraphicsView>
#include <QHBoxLayout>
#include <QMimeData>
#include <QMouseEvent>
#include <QTableView>
#include <QGraphicsPixmapItem>
#include <random>
#include <QStandardItemModel>
static std::random_device rd;
static std::mt19937 rng(rd());
class TableView: public QTableView{
public:
using QTableView::QTableView;
protected:
void mousePressEvent(QMouseEvent *event){
if (event->button() == Qt::LeftButton)
dragStartPosition = event->pos();
}
void mouseMoveEvent(QMouseEvent *event){
if (!(event->buttons() & Qt::LeftButton))
return;
if ((event->pos() - dragStartPosition).manhattanLength()
< QApplication::startDragDistance())
return;
QDrag *drag = new QDrag(this);
QMimeData *mimeData = new QMimeData;
// create image
QImage image(100, 100, QImage::Format_RGB32);
std::uniform_int_distribution<int> uni(0, 255);
image.fill(QColor(uni(rng), uni(rng), uni(rng)));
mimeData->setImageData(image);
drag->setPixmap(QPixmap::fromImage(image).scaled(10,10));
drag->setMimeData(mimeData);
drag->exec();
QTableView::mouseMoveEvent(event);
}
private:
QPoint dragStartPosition;
};
class Display: public QGraphicsView{
public:
using QGraphicsView::QGraphicsView;
protected:
void dragMoveEvent(QDragMoveEvent *event){
if(event->mimeData()->hasFormat("application/x-qt-image"))
event->acceptProposedAction();
}
void dropEvent(QDropEvent *event){
if (event->source() == this)
return;
QPixmap pixmap = qvariant_cast<QPixmap>(event->mimeData()->imageData());
QGraphicsPixmapItem *pixmap_item = scene()->addPixmap(pixmap);
pixmap_item->setPos(mapToScene(event->pos()));
event->acceptProposedAction();
}
};
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
QWidget w;
QHBoxLayout* lay = new QHBoxLayout(&w);
QGraphicsScene scene;
Display view(&scene);
view.setAcceptDrops(true);
TableView table;
QStandardItemModel model(10, 10);
table.setModel(&model);
lay->addWidget(&table);
lay->addWidget(&view);
w.show();
return a.exec();
}