Delphi - Form in DLL - Hints not showing

Question

I have a Delphi form inside a DLL (I know that this restricts the use of the DLL to Delphi but this is not a problem in this case).

The DLL exports a function ShowForm that looks roughly like this:

procedure ShowForm (App : TApplication);
begin
  OldApp := Application;
  try
    Application := App;
    MyForm := TMyForm.Create (nil);
    try
      MyForm.ShowModal;
    finally
      FreeAndNil (MyForm);
    end;
  finally
    Application := OldApp;
  end;
end;

Now on the form I use a TAdvOfficeHint (from the TMS component pack). Unfortunately the hints do not show up.

Am I missing something here? How can I make the form behave exactly as it would if I showed it from the main application?

Thanks!

Answer 1

I don't know TAdvOfficeHint but I guess it hooks Application.OnShowHint to set its own THintWindowClass, and even if both the main executable and the DLL are linking in the TMS unit, they each have their own copy of the class which is where things go wrong.

Assigning Application is not enough: there are other global variables, like Screen, Mouse, etc. Others are even hidden in the implementation so I'd say your chances to make the form behave exactly as from the main application are slim.

Answer 2

I guess in Delphi 2006 and later versions you can call System.ShareMemoryManager method in the EXE code, so that its memory manager is shared with other modules loaded in the process memory space.

Answer 3

Wrong setting of Application.

Try this and see if it solves your problem:

procedure ShowForm (AppHandle : THandle);
begin
  OldAppHandle := Application.Handle;
  try
    Application.Handle := AppHandle;
    ........
  finally
    Application.Handle := OldAppHandle;
  end;
end;

Answer 4

Just found the reason why it does not work. As TOndrej states, TAdvOfficeHinthooks Application.OnShowHint and internally executes the following line of code:

FHintInfo.Assign (AHintInfo);

Assign internally uses a dynamic type check

if (Source is TAddvHintInfo) then ...

which fails due to the separate type registries of the DLL and the main application.

I have run into this problem a few times now and maybe I really have to switch to runtime packages to avoid all this stuff.

Anyway, if there's anything I can do to prevent this, please comment.