Hier die Lösung
procedure SetSearchStringInListView(ListView:TListView;Searc hString:string);
var I: Integer;
SearchBox: TSearchBox;
begin
for I := 0 to ListView.Controls.Count-1 do
if ListView.Controls[I].ClassType = TSearchBox then
begin
SearchBox := TSearchBox(ListView.Controls[I]);
SearchBox.Text := SearchString;
SearchBox.SetFocus;
Break;
end;
end;