private void ShowCalls(CallHierarchyExplorerViewManager manager,
                               Func <CallHierarchyFindResult, bool> filter,
                               DeclaredElementInstance <IClrDeclaredElement> start,
                               ShowCallsType callType)
        {
            var text = Text;

            switch (callType)
            {
            case ShowCallsType.INCOMING:
                text += " to " + start.Element.ShortName;
                manager.ShowIncoming(start, text, filter);
                break;

            case ShowCallsType.OUTGOING:
                text += " from " + start.Element.ShortName;
                manager.ShowOutgoing(start, text, filter);
                break;

            default:
                throw new ArgumentOutOfRangeException();
            }
        }