Workaround for StandardItemModel drag drop bug

[onamatic]

I have a QTreeView with a QStandardItemModel implementing a simple "notebook" type of application (ie: a bunch of notes inside a bunch of folders).

Everything is fine except for internally drag/dropping a folder in the treeview when all the notes in the dragged folder get lost.
This is a known bug and is detailed here: Drag and drop in QTreeView with QStandardItemModel and InternalMove loses children

Without this functionality I'm truly stuck, so I'm now subclassing QStandardItemModel

class QNotesStandardItemModel : public QStandardItemModel

class QNotesStandardItemModel : public QStandardItemModel

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and trying to manually sort things out in:

bool QNotesStandardItemModel::dropMimeData ( const QMimeData * data, Qt::DropAction action, int row, int column, const QModelIndex & parent ){
	QStringList list = data->formats();
	if (!data->hasFormat("application/x-qabstractitemmodeldatalist")) return false;
	QByteArray encodedData = data->data("application/x-qabstractitemmodeldatalist");

bool QNotesStandardItemModel::dropMimeData ( const QMimeData * data, Qt::DropAction action, int row, int column, const QModelIndex & parent ){
	QStringList list = data->formats();
	if (!data->hasFormat("application/x-qabstractitemmodeldatalist")) return false;
	QByteArray encodedData = data->data("application/x-qabstractitemmodeldatalist");

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And now I'm stuck!
QUESTION 1: encodedData contains a QList<QModelIndex> but how do I get at it? I want a kind of "qobject_cast<QModelIndexList>(encodedData)" type of thing! Just can't see how though.

QUESTION 2: Is there an easy way of working round the "lost children" problem? I really wanted to keep this application as simple as possible and not have to subclass standard classes which generally work fine out of the box.

[caduel]

Re Q1:
If you use drag-n-drop between two different applications, the QModelIndexes will not be of much use to you.
If you drag within a single application, just create a subclass of QDrag or QMimeData and add a QList<QModelIndex> to it. Then (at the drop site) cast the object back to your class and access the QModelIndexes. (No need to go through encode/decode troubles within a single application.)

HTH

[onamatic]

Thanks for helping me Caduel!

Re Q1:
If you use drag-n-drop between two different applications, the QModelIndexes will not be of much use to you.

Understood, I'm only drag-n-dropping inside a single treeview so that's fine.

...Then (at the drop site) cast the object back to your class and access the QModelIndexes. (No need to go through encode/decode troubles within a single application.)

There's my problem - I can't see how to cast from the QByteArray returned by the call to mimeDataPtr->data() to the "application/x-qabstractitemmodeldatalist" that I want. I'm missing something conceptually here I think!

[caduel]

I was suggesting to not use that QByteArray at all.

class MyMimeData : public QMimeData
{
   QModelIndexList indexes;
public:
   MyMimeData(const QModelIndexList & indexes)
   : indexes_(indexes)
   {}
   const QModelIndexList & indexes() const { return indexes_; }
};
 
QMimeData * QNotesStandardItemModel::mimeData(const QModelIndexList &indexes) const 
{
// maybe set a mimetype...
// but finally
     return new MyMimeData(indexes);
}
 
bool QNotesStandardItemModel::dropMimeData ( const QMimeData * data, Qt::DropAction action, int row, int column, const QModelIndex & parent )
{
    if (MyMimeData *mmd = qobject_cast<MyMimeData>(data))
    {
        // access dragges indexes as: mmd->indexes()
        // ...
        return true;
    }
    return false;
}

class MyMimeData : public QMimeData
{
   QModelIndexList indexes;
public:
   MyMimeData(const QModelIndexList & indexes)
   : indexes_(indexes)
   {}
   const QModelIndexList & indexes() const { return indexes_; }
};

QMimeData * QNotesStandardItemModel::mimeData(const QModelIndexList &indexes) const 
{
// maybe set a mimetype...
// but finally
     return new MyMimeData(indexes);
}

bool QNotesStandardItemModel::dropMimeData ( const QMimeData * data, Qt::DropAction action, int row, int column, const QModelIndex & parent )
{
    if (MyMimeData *mmd = qobject_cast<MyMimeData>(data))
    {
        // access dragges indexes as: mmd->indexes()
        // ...
        return true;
    }
    return false;
}

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HTH

[onamatic]

That works brilliantly. Thank you very much Caduel for taking the time to write my code for me! Much appreciated.

Bob