Newly created modal window loses focus and become inacessible in Windows Vista

Question

Sometimes when I open a modal window in my Delphi application it takes a while to show up, then I notice that the application is kind of blocked, and what happened was that the modal form was open with ShowModal but wasn't displayed and the application became locked as if the Modal Window was in the first layer.

Usually when this happens I have to use Alt + Tab or Windows + Tab to find the "hidden" modal window, but this doesn't work everytime.

This behavior just happens in Vista, but its quite annoying.

Is there some way to prevent this "focus weirdness" from happening?

Thanks.

* EDIT *

Apparently setting Application.MainFormOnTaskbar := True solved the problem, but it is still too early to jump to conclusions because this happens randomly.

* EDIT 2 *

ModalFormOnTaskbar didn't solve the problem, after that I tried setting PopupMode = pmAuto , but that just made the problem worst.

Right now I'm trying to set the PopupParent explicitly and will let you know if the problem is solved.

Answer 1

Take a look at the PopupParent property. You may want to set it explicitly for your modal form prior to the ShowModal call. When PopupParent is nil (default) VCL behaves a bit differently depending on the value of the related PopupMode property.

If you set the modal form's PopupParent to the form that's active just before you call ShowModal, that may help.

Answer 2

I've seen the same thing under XP and I've seen it with various commercial programs, also. It appears to be timing related.

Answer 3

The issue you have started happening when Windows XP introduced the concept of window ghosting. Due to the unusual architecture Delphi uses (all forms are children of a hidden window — TApplication) many Delphi applications experience the same problem.

One way to quickly solve it is to disable window ghosting when initializing the application:

var 
  User32: HMODULE; 
  DisableProcessWindowsGhosting: TProcedure; 
begin 
  User32 := GetModuleHandle('USER32'); 
  if User32 <> 0 then 
  begin 
    DisableProcessWindowsGhosting := GetProcAddress(User32, 'DisableProcessWindowsGhosting'); 
    if Assigned(DisableProcessWindowsGhosting) then 
      DisableProcessWindowsGhosting; 
  end; 
end;

Another possible (more elegant though laborious) solution is to normalize your Delphi application.

A third option would be switching to Delphi 2006 (Delphi 10.0).

Besides the issue you're reporting Delphi's architecture introduces more oddities, among them the different task bar menu and the inability to flash.

Answer 4

I am using D2006 and this issue has now started on the majority of our machines. I have tried several solutions (not the above yet) but nothing seems to help - I have made each window have its own entry on the task bar so users can click back on the task bar icon but its becoming a real issue for me.

Answer 5

you may want to try add the code below into your TCustomForm.ShowModal: just before Application.ModalStarted call:

if Assigned(Application) then begin while PeekMessage(msg, Application.Handle, CM_ACTIVATE, CM_DEACTIVATE, PM_REMOVE) do begin TranslateMessage(msg); DispatchMessage(msg); end; end;