+wxSize wxGenericTreeCtrl::DoGetBestSize() const
+{
+ // make sure all positions are calculated as normally this only done during
+ // idle time but we need them for base class DoGetBestSize() to return the
+ // correct result
+ wxConstCast(this, wxGenericTreeCtrl)->CalculatePositions();
+
+ wxSize size = wxTreeCtrlBase::DoGetBestSize();
+
+ // there seems to be an implicit extra border around the items, although
+ // I'm not really sure where does it come from -- but without this, the
+ // scrollbars appear in a tree with default/best size
+ size.IncBy(4, 4);
+
+ // and the border has to be rounded up to a multiple of PIXELS_PER_UNIT or
+ // scrollbars still appear
+ const wxSize& borderSize = GetWindowBorderSize();
+
+ int dx = (size.x - borderSize.x) % PIXELS_PER_UNIT;
+ if ( dx )
+ size.x += PIXELS_PER_UNIT - dx;
+ int dy = (size.y - borderSize.y) % PIXELS_PER_UNIT;
+ if ( dy )
+ size.y += PIXELS_PER_UNIT - dy;
+
+ // we need to update the cache too as the base class cached its own value
+ CacheBestSize(size);
+
+ return size;
+}
+