Drag & drop in QTreeWidget

Maluna34

Hello ! :)

(Sorry for my english)

I am currently trying to make a drag & drop in a QTreeWidget. So I put the corresponding settings and the method dropEvent :

class TreeWidget : public QTreeWidget
{
protected:

  virtual void dropEvent(QDropEvent *event) override
  {
    QModelIndex index = indexAt(event->pos());
    if (!index.isValid()) {  // just in case
      event->setDropAction(Qt::IgnoreAction);
      return;
    }

    QTreeWidgetItem* item = itemFromIndex(index);
    qDebug() << "drop on item" << item->text(0);

    QTreeWidget::dropEvent(event);
  }
};

int main()
{
  TreeWidget *listWidget = new TreeWidget;
  listWidget->setSelectionMode(QAbstractItemView::SingleSelection);
  listWidget->setDragEnabled(true);
  listWidget->viewport()->setAcceptDrops(true);
  listWidget->setDropIndicatorShown(true);
  listWidget->setDragDropMode(QAbstractItemView::InternalMove);
}

But in my case, I would like to move only parent items. In the code, I get the destination item, but how get dragged item ?

Have I to overload a drag method ? Launch the drag myself from mousePressEvent ? What is the best way to do ?

Thanks !

jsulm

@Maluna34 http://doc.qt.io/qt-5/qdropevent.html#source should be what you're looking for.

Maluna34

@jsulm Thank you but I can't cast QObject to QTreeWidgetItem. :/

jsulm

@Maluna34 You can (if it is a QTreeWidgetItem). And it is QObject* not QObject.
Take a look at http://doc.qt.io/qt-5/qobject.html#qobject_cast

raven-worx

@jsulm
source() only returns a widget of the same application as the docs clearly say.

The QTreeWidgetItem data is "encoded" in the drop-data (QMimeData) itself.
See source of QStandardItemModel::dropMimeData() and QStandardItemModelPrivate::decodeDataRecursive()
So unfortunately this is not accessible via public API.

Maluna34

@raven-worx Thank you ! Indeed, I manage to get the item text with this code :

virtual void dropEvent(QDropEvent *event) override
{
        QString format = event->mimeData()->formats().at(0);
        QByteArray data = event->mimeData()->data(format);
        QDataStream stream(&data, QIODevice::ReadOnly);

        int r, c;
        QStandardItem *sitem = new QStandardItem;
        stream >> r >> c >> *sitem;

        qDebug() << r << "-" << c << sitem->text();
}

I think it's correct. Maybe it's also possible to get either the depth of the element or get the right type (QTreeWidgetItem).

Maluna34

The best way seems to use QDropEvent::source to get the QTreeWidget and use currentItem() on it. :)