Qt5 drag 'n drop problem : dropEvent never called

Hi all,

I'm facing a problem with Drag 'N Drop : I started my design using Fridge Magnets exemple. But now I'm trying to integrate the modified code to my main app. Thing is I can't drop my widget anymore. I suspect it has to do with the fact that I'm now trying to drag 'n drop my widgets on a QFrame, whereas on the Qt Exemple it doesn't go like that.

I've pasted some code :

Code:

---

BeaconWidgetDrag::BeaconWidgetDrag(QWidget *parent)
    : QWidget(parent)
{
    BeaconWidget * test;
 
    int x = 5;
    int y = 5;
 
    test = new BeaconWidget("x01", BeaconStateDown, this);
 
    test->move(x, y);
    test->show();
    test->setAttribute(Qt::WA_DeleteOnClose);
 
    //setMinimumSize(400, qMax(200, y));
    setAcceptDrops(true);
}
 
BeaconWidgetDrag::~BeaconWidgetDrag()
{
 
}
 
void BeaconWidgetDrag::dragEnterEvent(QDragEnterEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-beaconwidget")) {
        if (children().contains(event->source())) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else if (event->mimeData()->hasText()) {
        event->acceptProposedAction();
    } else {
        event->ignore();
    }
}
 
void BeaconWidgetDrag::dragMoveEvent(QDragMoveEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-beaconwidget")) {
        if (children().contains(event->source())) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else if (event->mimeData()->hasText()) {
        event->acceptProposedAction();
    } else {
        event->ignore();
    }
}
 
void BeaconWidgetDrag::dropEvent(QDropEvent *event)
{
    if (event->mimeData()->hasFormat("application/x-beaconwidget")) {
        const QMimeData *mime = event->mimeData();
        QByteArray itemData = mime->data("application/x-beaconwidget");
        QDataStream dataStream(&itemData, QIODevice::ReadOnly);
 
        QString text;
        QPoint offset;
        dataStream >> text >> offset;
        BeaconWidget * newBeacon = new BeaconWidget(text, BeaconStateDown, this);
        newBeacon->move(event->pos() - offset);
        newBeacon->show();
        newBeacon->setAttribute(Qt::WA_DeleteOnClose);
 
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else if (event->mimeData()->hasText()) {
        QStringList pieces = event->mimeData()->text().split(QRegExp("\\s+"),
                             QString::SkipEmptyParts);
        QPoint position = event->pos();
 
        foreach (QString piece, pieces) {
            BeaconWidget * newBeacon = new BeaconWidget(piece, BeaconStateDown, this);
            newBeacon->move(position);
            newBeacon->show();
            newBeacon->setAttribute(Qt::WA_DeleteOnClose);
 
            position += QPoint(newBeacon->width(), 0);
        }
 
        event->acceptProposedAction();
    } else {
        event->ignore();
    }
}
 
void BeaconWidgetDrag::mousePressEvent(QMouseEvent * event)
{
    BeaconWidget *child = static_cast<BeaconWidget *>(childAt(event->pos()));
    if (!child)
        return;
 
    QPoint hotSpot = event->pos() - child->pos();
 
    QByteArray itemData;
    QDataStream dataStream(&itemData, QIODevice::WriteOnly);
    dataStream << child->labelText() << QPoint(hotSpot);
 
    QMimeData *mimeData = new QMimeData;
    mimeData->setData("application/x-beaconwidget", itemData);
    mimeData->setText(child->labelText());
 
    QDrag *drag = new QDrag(this);
    drag->setMimeData(mimeData);
    drag->setPixmap(*child->pixmap());
    drag->setHotSpot(hotSpot);
 
    child->hide();
 
    if (drag->exec(Qt::MoveAction | Qt::CopyAction, Qt::CopyAction) == Qt::MoveAction)
        child->close();
    else
        child->show();
}
 
 
void BeaconWidgetDrag::Log(QString s)
{
    emit LogChanged(s);
}

---

My drag 'n drop widget is called that way, with ui->frame being a QFrame with setAcceptDrops = true

Code:

---

void BeaconMonitor::on_tabWidget_tabBarDoubleClicked(int index)
{
    BeaconWidgetDrag * beaconWidgetDrag = new BeaconWidgetDrag(ui->frame);
    beaconWidgetDrag->show();
}

---

I hope I have been clear enough.

Thanks for your help;

Are drag enter and move event handlers being called?

Yes I checked with GDB that drag "enter" and "move" event handlers are called. I still don't have a clue...

I found the solution : basically what I was trying to do was to have the widget a parent (ie. QFrame) while calling the constructor. I didn't consider the fact that you could add the BeaconWidgetDrag object directly to a Layout with addWidget.