how to port a QAbstractItemModel to QtQuick (without defining ItemDelegate) - qt

Question

I have a QAbstractItemModel tree model for a Qt3D Entity tree:
qt3dentitytreemodel.h:
#define QT3DENTITYTREEMODEL_H
#include <QAbstractItemModel>
#include <Qt3DCore/QEntity>
class Qt3DEntityTreeModel : public QAbstractItemModel
{
Q_OBJECT
public:
Q_PROPERTY(Qt3DCore::QEntity * rootEntity READ rootEntity WRITE setRootEntity NOTIFY rootEntityChanged)
explicit Qt3DEntityTreeModel(QObject *parent = nullptr);
void setRootEntity(Qt3DCore::QEntity *rootEntity);
Qt3DCore::QEntity * rootEntity() const;
QModelIndex index(int row, int column, const QModelIndex &parent = QModelIndex()) const override;
QModelIndex parent(const QModelIndex &child) const override;
QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const override;
QVariant headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const override;
int rowCount(const QModelIndex &parent = QModelIndex()) const override;
int columnCount(const QModelIndex &parent = QModelIndex()) const override;
Qt::ItemFlags flags(const QModelIndex &index) const override;
signals:
void rootEntityChanged(Qt3DCore::QEntity *rootEntity);
private:
Qt3DCore::QEntity *rootEntity_;
};
#endif // QT3DENTITYTREEMODEL_H
qt3dentitytreemodel.cpp:
#include "qt3dentitytreemodel.h"
Qt3DEntityTreeModel::Qt3DEntityTreeModel(QObject *parent)
: QAbstractItemModel(parent)
{
}
void Qt3DEntityTreeModel::setRootEntity(Qt3DCore::QEntity *rootEntity)
{
qDebug() << "Qt3DEntityTreeModel::setRootEntity" << rootEntity;
auto old = rootEntity_;
rootEntity_ = rootEntity;
if(rootEntity_ != old)
emit rootEntityChanged(rootEntity);
}
Qt3DCore::QEntity * Qt3DEntityTreeModel::rootEntity() const
{
return rootEntity_;
}
QModelIndex Qt3DEntityTreeModel::index(int row, int column, const QModelIndex &parent) const
{
if(!rootEntity_) return {};
if(column != 0) return {};
if(!parent.isValid())
{
if(row == 0) return createIndex(0, 0, rootEntity_);
}
else
{
auto entity = reinterpret_cast<Qt3DCore::QEntity*>(parent.internalPointer());
if(!entity) return {};
return createIndex(row, column, entity->childNodes().at(row));
}
return {};
}
QModelIndex Qt3DEntityTreeModel::parent(const QModelIndex &child) const
{
if(!rootEntity_) return {};
if(!child.isValid()) return {};
auto entity = reinterpret_cast<Qt3DCore::QEntity*>(child.internalPointer());
if(!entity) return {};
auto parent = entity->parentNode();
if(!parent) return {};
auto grandParent = parent->parentNode();
if(!grandParent) return createIndex(0, 0, parent);
return createIndex(grandParent->childNodes().indexOf(parent), 0, parent);
}
QVariant Qt3DEntityTreeModel::data(const QModelIndex &index, int role) const
{
if(!rootEntity_) return {};
if(!index.isValid()) return {};
if(role != Qt::DisplayRole && role != DisplayRole) return {};
auto entity = reinterpret_cast<Qt3DCore::QEntity*>(index.internalPointer());
if(!entity) return {};
QString data = entity->metaObject()->className();
if(!entity->objectName().isEmpty())
data += QString(" \"%1\"").arg(entity->objectName());
return data;
}
QVariant Qt3DEntityTreeModel::headerData(int section, Qt::Orientation orientation, int role) const
{
return {};
}
int Qt3DEntityTreeModel::rowCount(const QModelIndex &parent) const
{
if(!parent.isValid()) return 1;
auto entity = reinterpret_cast<Qt3DCore::QEntity*>(parent.internalPointer());
if(!entity) return 0;
return entity->childNodes().count();
}
int Qt3DEntityTreeModel::columnCount(const QModelIndex &parent) const
{
return 1;
}
Qt::ItemFlags Qt3DEntityTreeModel::flags(const QModelIndex &index) const
{
return {};
}
which works fine when displayed in a QTreeView (QtWidgets):
auto treeView = new QTreeView();
auto treeModel = new Qt3DEntityTreeModel(treeView);
treeModel->setRootEntity(rootEntity);
treeView->setModel(treeModel);
treeView->resize(640, 480);
treeView->show();
however when used in a QtQuick Controls TreeView, I cannot see the item text, and I cannot even expand the root tree item:
Item {
...
Qt3DEntityTreeModel {
id: entityTreeModel
rootEntity: root
}
TreeView {
model: entityTreeModel
TableViewColumn {
title: "Name"
width: 200
}
}
Scene3D {
id: scene3d
Entity {
id: root
...
}
}
}
I also tried to explicitly define a role in Qt3DEntityTreeModel:
qt3dentitytreemodel.h:
enum Roles {
DisplayRole = Qt::UserRole + 1
};
QHash<int, QByteArray> roleNames() const override;
qt3dentitytreemodel.cpp:
QVariant Qt3DEntityTreeModel::data(const QModelIndex &index, int role) const
{
if(!rootEntity_) return {};
if(!index.isValid()) return {};
if(role != Qt::DisplayRole && role != DisplayRole) return {};
...
}
QHash<int, QByteArray> Qt3DEntityTreeModel::roleNames() const
{
QHash<int, QByteArray> result;
result.insert(DisplayRole, QByteArrayLiteral("display"));
return result;
}
and define the respective role property in the column of the QtQuick TreeView:
TreeView {
model: entityTreeModel
TableViewColumn {
title: "Name"
role: "display"
width: 200
}
}
but still shows nothing.
Is there something else to do to be able to use a custom abstract item model with QtQuick's TreeView?

Answer 1

I think I found the explanation: the model is created before the Qt3D entity tree is "ready".
If I create the model in C++ after the view is loaded, then set the model as a context property, it displays correctly in the QML's TreeView:
QQuickView view;
view.resize(500, 500);
view.setResizeMode(QQuickView::SizeRootObjectToView);
view.setSource(QUrl("qrc:/main.qml"));
auto rootObject = view.rootObject();
auto rootEntity = rootObject->findChild<Qt3DCore::QEntity*>("theRootEntity");
qDebug() << "rootEntity:" << rootEntity;
auto treeModel = new Qt3DEntityTreeModel(&app);
treeModel->setRootEntity(rootEntity);
view.rootContext()->setContextProperty("theModel", treeModel);
view.show();
The fundamental problem is that my model doesn't monitor updates to the Qt3D entity tree, and it does not reflect such updates.