How to ungroup popup window from the application on the taskbar?

Is it possible to instruct the shell taskbar to exclude a certain hwnd popup window from the main application's button "group"?

I have a "stopwatch" popup window. On my machine, with taskbar button combining disabled, the windows appears exactly as i'd like it: a separate item on the taskbar:

enter image description here

But if the user uses (the default, and most corporations prevent users from altering their personal preferences), the separate window is not visible:

enter image description here

Now, i am using ITaskbarList3.SetOverlayIcon to specify an overlay icon for my popup window:

list: ITaskbarList3;

list := CoTaskbarList3.Create;
list.SetOverlayIcon(windowHandle, ico, '');

so Windows will at least do me the favour of picking the most recent overlay icon, and applying it to the combined visual group - which is nice.

But i'd still prefer to have this separate action in a separate item on the taskbar.

One horrible workaround would be to ship another executable with my application; one just to fool the grouper into putting this other hwnd in its own group. But that's not something i want to do.

Why would i think i'm allowed to do this?

I was surprised to learn that you are allowed to prevent the user from pinning an application to the taskbar.

And while the MSDN page on shell programming doesn't give an example specifically for what i want, that doesn't mean it's not out there. It just might mean that it's all poorly documented.

Solution

In my case, the "operator" has a stopwatch. When they start the stopwatch, i pop out the form of the application group by giving it a different User Model Application ID:

SetWindowAppModelUserID('Contoso.Frobber.Stopwatch');

and immediately the form pops out:

enter image description here

When the user stops (or pauses) the stopwatch, i let the window coalesce back into the application:

SetWindowAppModelUserID('');

enter image description here

Caveats

You don't actually set the AppModelUserID to an empty string; that is not a valid application identifer. Instead you set it to VT_EMPTY. My helpful wrapper function checks for '', and converts it into a VT_EMPTY value.

Another warning comes from the SDK:

A window's properties must be removed before the window is closed. If this is not done, the resources used by those properties are not returned to the system. A property is removed by setting it to the PROPVARIANT type VT_EMPTY.

This means that care needs to be taken to remove a custom property applied to an HWND before i destroy it. A somewhat daunting task; one that i will almost certainly screw up.

The Code

function TFormEx.SetWindowAppModelUserID(const AppModelUserID: WideString): HRESULT;
var
   ps: IPropertyStore;
   value: OleVariant;
const
   PKEY_AppUserModel_ID: TPropertyKey = ( fmtid: '{9F4C2855-9F79-4B39-A8D0-E1D42DE1D5F3}'; pid: 5);
begin
   Result := SHGetPropertyStoreForWindow(Self.Handle, IPropertyStore, {out}ps);
   if Failed(Result) then Exit;

   if (ps = nil) then
   begin
      Result := E_FAIL;
      Exit;
   end;

   if AppModelUserID <> '' then
   begin
      value := AppModelUserID;
      Result := ps.SetValue(PKEY_AppUserModel_ID, PROPVARIANT(value));
   end
   else
   begin
      {
         A window's properties must be removed before the window is closed.
         If this is not done, the resources used by those properties are not returned to the system.
         A property is removed by setting it to the PROPVARIANT type VT_EMPTY.
      }
      value := Unassigned; //the VT_EMPTY type
      Result := ps.SetValue(PKEY_AppUserModel_ID, PROPVARIANT(value));
   end;
end;

Bonus Reading

Note: Any code released into public domain. No attribution required.