+void wxTreeCtrlBase::SetItemState(const wxTreeItemId& item, int state)
+{
+    if ( state == wxTREE_ITEMSTATE_NEXT )
+    {
+        int current = GetItemState(item);
+        if ( current == wxTREE_ITEMSTATE_NONE )
+            return;
+        state = current + 1;
+        if ( m_imageListState && state >= m_imageListState->GetImageCount() )
+            state = 0;
+    }
+    else if ( state == wxTREE_ITEMSTATE_PREV )
+    {
+        int current = GetItemState(item);
+        if ( current == wxTREE_ITEMSTATE_NONE )
+            return;
+        state = current - 1;
+        if ( state == -1 )
+            state = m_imageListState ? m_imageListState->GetImageCount() - 1 : 0;
+    }
+    // else: wxTREE_ITEMSTATE_NONE depending on platform
+
+    DoSetItemState(item, state);
+}
+
+static void
+wxGetBestTreeSize(const wxTreeCtrlBase* treeCtrl, wxTreeItemId id, wxSize& size)
+{
+    wxRect rect;
+
+    if ( treeCtrl->GetBoundingRect(id, rect, true /* just the item */) )
+    {
+        // Translate to logical position so we get the full extent
+#if defined(__WXMSW__) && !defined(__WXUNIVERSAL__)
+        rect.x += treeCtrl->GetScrollPos(wxHORIZONTAL);
+        rect.y += treeCtrl->GetScrollPos(wxVERTICAL);
+#endif
+
+        size.IncTo(wxSize(rect.GetRight(), rect.GetBottom()));
+    }
+
+    wxTreeItemIdValue cookie;
+    for ( wxTreeItemId item = treeCtrl->GetFirstChild(id, cookie);
+          item.IsOk();
+          item = treeCtrl->GetNextChild(id, cookie) )
+    {
+        wxGetBestTreeSize(treeCtrl, item, size);
+    }
+}
+