Changing the window style of a component

The CreateParams method is used to set the window style of the component and its parameters that must be passed to the CreateWindowEx API. To change the window style of a component, such as adding or taking off a vertical reel of a component, simply rewrite the CreateParams method:

procedure TMyControl.CreateParams(var Params: TCreateParams);
begin
inherited CreateParams(Params);
if IWantAScrollBar then
Params.Style := Params.Style or WS_VSCROLL
else
Params.Style := Params.Style and not WS_VSCROLL;
end