Qt3DRender::QMesh * mesh = new Qt3DRender::QMesh();
 QUrl url("pathto/mesh.obj");
 mesh->setSource( url );
if (mesh->source().isEmpty()) {
 throw std::runtime_error("A source is needed to build the geometry.");
 }
Qt3DRender::QGeometryFactory *geometry_factory = mesh->geometryFactory().data(); // << mesh->geometryFactory().data() returns null pointer
 if (!geometry_factory) {
 throw std::runtime_error("Could not construct geometry from mesh: " +
 mesh->source().toString().toStdString());
 }
 Qt3DRender::QGeometry *geometry = geometry_factory->operator()();

void QMesh::setSource(const QUrl& source)
{
 Q_D(QMesh);
 if (d->m_source == source)
 return;
 d->m_source = source;
 // update the functor
 QGeometryRenderer::setGeometryFactory(QGeometryFactoryPtr(new MeshFunctor(d->m_source, d->m_meshName)));
 const bool blocked = blockNotifications(true);
 emit sourceChanged(source);
 blockNotifications(blocked);
}

void QMesh::setSource(const QUrl& source)
{
 Q_D(QMesh);
 if (d->m_source == source)
 return;
 d->m_source = source;
 d->updateFunctor();
 const bool blocked = blockNotifications(true);
 emit sourceChanged(source);
 blockNotifications(blocked);
}

void QMeshPrivate::updateFunctor()
{
 Q_Q(QMesh);
 Qt3DCore::QAspectEngine *engine = m_scene ? m_scene->engine() : nullptr;
 if (engine)
 q->setGeometryFactory(QGeometryFactoryPtr(new MeshLoaderFunctor(q, engine)));
}