wxDataViewItem GetPrevItem( wxDataViewCtrl const& aView, wxDataViewItem const& aItem )
{
    auto prevItem = GetPrevSibling( aView, aItem );

    if( !prevItem.IsOk() )
    {
        prevItem = aView.GetModel()->GetParent( aItem );
    }
    else if( aView.IsExpanded( prevItem ) )
    {
        wxDataViewItemArray children;
        aView.GetModel()->GetChildren( prevItem, children );
        prevItem = children[children.size() - 1];
    }

    return prevItem;
}
wxDataViewItem GetNextItem( wxDataViewCtrl const& aView, wxDataViewItem const& aItem )
{
    wxDataViewItem nextItem;

    if( !aItem.IsOk() )
    {
        // No selection. Select the first.
        wxDataViewItemArray children;
        aView.GetModel()->GetChildren( aItem, children );
        return children[0];
    }

    if( aView.IsExpanded( aItem ) )
    {
        wxDataViewItemArray children;
        aView.GetModel()->GetChildren( aItem, children );
        nextItem = children[0];
    }
    else
    {
        // Walk up levels until we find one that has a next sibling.
        for( wxDataViewItem walk = aItem; walk.IsOk(); walk = aView.GetModel()->GetParent( walk ) )
        {
            nextItem = GetNextSibling( aView, walk );

            if( nextItem.IsOk() )
                break;
        }
    }

    return nextItem;
}