Say ViewA has ProxyModelA and selection model "SelectModelA".
ViewB would like share SelectModelA with viewA.
However ViewB uses a different model, say ProxyModelB.
Both ProxyModelA and ProxyModelB sit on top (say directly for the time being) of the real deal - call it "ModelRoot".

When it comes to selection, viewB will receive model indexes from "ProxyModelA". viewB doesn't understand "ProxyModelA". So it has to either convert it or a conversion has to take place between.

Case 1 might look like the following since the model ptr is part of the modelindex (if this utterly horrible, say so!)

@
...
connect(standard_qtreeview_selection_model,SIGNAL(currentRowChanged(QModelIndex,QModelIndex)),
my_graphics_scene,SLOT(slot_model_select(QModelIndex,QModelIndex)));
...

void MyGraphicsScene::slot_model_select(const QModelIndex& idx_in,
const QModelIndex& prev_idx_in)
{
QModelIndex idx = idx_in;
QModelIndex prev_idx = prev_idx_in;

const QAbstractProxyModel* pmodel = dynamic_cast<const QAbstractProxyModel*>
                                    (idx.model());
if ( pmodel ) {
    idx = pmodel->mapToSource(idx_in);
    prev_idx = pmodel->mapToSource(prev_idx_in);
}

@

Another example, in the case of a Delegate that launches an editor which is a qtableview, the delegate may create a little proxy model based on the current model which could be a proxy itself... and well it's complicated to explain the interaction with the selection model... ughh

The thing is, I can do this, I just feel off... and hoping there was some advice.