QListView moveRow() from model not called - qt

Question

I'm having a Listview which should show a preview of an image. For this I created a the item "ListItem"
class ListItem
{
public:
ListItem();
ListItem(QString name, QImage image);
QImage* previewIcon();
void setPreviewIcon(QImage icon);
QImage *image();
void setImage(QImage* image);
void setImage(QImage image);
void setName(QString name);
void setChecked(bool checked);
QString name();
bool checked();
private:
QImage m_preview;
QImage m_image;
QString m_name;
bool m_checked;
};
This model stores the image it self and a preview of it. This works fine for inserting and removing items:
class ListModel: public QAbstractListModel
{
Q_OBJECT
public:
ListModel(QObject *parent = nullptr);
int rowCount(const QModelIndex &parent = QModelIndex()) const override;
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
bool setData(const QModelIndex &index, const QVariant &value, int role = Qt::EditRole) override;
Qt::ItemFlags flags(const QModelIndex &index) const override;
QModelIndex index(int row, int column = 0, const QModelIndex &parent = QModelIndex()) const override;
bool removeRow(int row, const QModelIndex &parent = QModelIndex());
bool removeRows(int row, int count, const QModelIndex &parent = QModelIndex()) override;
bool insertRow(int row, const QModelIndex &parent = QModelIndex());
bool insertRows(int row, int count, const QModelIndex &parent = QModelIndex()) override;
bool appendItem(ListItem* item);
bool moveRows(const QModelIndex &sourceParent, int sourceRow, int count, const QModelIndex &destinationParent, int destinationChild) override;
bool moveRow(const QModelIndex &sourceParent, int sourceRow, const QModelIndex &destinationParent, int destinationChild);
Qt::DropActions supportedDropActions() const override;
QHash<int, QByteArray> roleNames() const override;
private:
ListItem* getItem(const QModelIndex &index) const;
private:
QList<ListItem*> m_scannedDocuments;
};
This is the setup of the QListView:
m_scannedDocumentsModel = new ListModel();
m_scannedDocuments = new QListView();
m_scannedDocuments->setModel(m_scannedDocumentsModel);
m_scannedDocuments->setDragDropMode(QAbstractItemView::InternalMove);
m_scannedDocuments->setMovement(QListView::Snap);
m_scannedDocuments->setDefaultDropAction(Qt::MoveAction);
Dragging and droping is fine for the preview, the name and if it is checked or not. The problem is the image "m_image". When I'm doing a move in the view, the view calls insertRows() and inserts a new item and removes the old item, but does not call moveRows.
Why moveRows() is not called?
Here you can find the full implementation:
ListModel.cpp
ListModel.h
Another approach would be to create a userRole for the image it self. Here I tried to reimplement roleNames() as
QHash<int, QByteArray> ListModel::roleNames() const {
QHash<int, QByteArray> roles = QAbstractItemModel::roleNames();
roles[Qt::UserRole] = "Qt::UserRole";
return roles;
}
and check the roles in setdata()/data() but this didn't work either.
What is the best way to have a complex model and moving them in a listview?

Answer 1

As already answered in brief on the Qt interest list:
Because moveRows was added in Qt 5.x, and drag and drop in Qt 4, and still uses insert+remove for backwards compatibility.
I'd add that "moveRows" is I guess considered an "optimization" and not really a requirement for a model, and the view has no way to know if the move methods are really implemented. Since an editable model requires remove/insert functions, it's "safer" to call those by default.
You can re-implement the model's dropMimeData() method and call moveRows() yourself. But, the caveat is you should return false from the method if you do this. If you return true to a Qt::MoveAction, the view will still try to remove the row from the old position in the model (which is obviously not what you want).