How to prevent form from being activated when the users clicks on it?

Question

I have a main form and non-modal autocomplete form. How can I prevent the autocomplete form from being activated by the user, when the user clicks on the list in the autocomplete form?

So, basically I want the autocomplete form the receive the mouse click message when the users clicks, but to never become active, because it causes problems with a third-party component in the main form over which I have no control.

Answer 1

Override CreateParams method of your form and add WS_EX_NOACTIVATE style to the extended styles.

procedure TForm1.CreateParams(var Params: TCreateParams);
begin
  inherited;

  Params.WindowClass.ExStyle := Params.WindowClass.ExStyle or WS_EX_NOACTIVATE;
end;

(code written from memory, might contain typos)

Answer 2

Use CreateParams (Alex T. answer) or you can try set YourForm.Enabled to False.