The Access Violation is raised when the form with Grid inside a DLL is closed

Each of my Dll's is providing a single form that is created by the host immediately after loading the dll.
So i had dxInitialize in the constructor and dxFinalize in the destructor of the dll's form base class.

On your advice I moved it to the initialization and finalization parts of the forms unit … no success.

When should dxInitialize and dxFinalize be called?
Once for the host and once for each dll I'm loading?
Or only once by the host as all the loaded dll's are loaded into the host's address space?

My own solution is working quite good so far ;-)

Thank you for letting us know that you have found the workaround.

I've examined your code further and wish to give you some comments:

1. I need to note that the following approach is incorrect:

Delphi
constructor TClientForm.Create(AOwner: TForm);  
begin  
  dxInitialize;  
  inherited CreateParented(AOwner.Handle);  
  Self.MainForm := AOwner as IMainForm;  
end;  

destructor TClientForm.Destroy;  
begin  
  dxFinalize;  
  inherited Destroy;  
end;  

You need to call the initialization before creating any controls.
Also, you need to export our dxInitialize and dxFinalize procedures like the CreateForm one:

Delphi
library Module3;  

...  

Exports  
  dxInitialize,  
  dxFinalize,  
  CreateForm;  

2. I see that you never use the FreeLibrary method, so it is unclear where you unload your library.

3. The "Access Violation" exception is raised because of your TModuleFactory.CreateModule function:

Delphi
class function TModuleFactory.CreateModule(ParentForm: TForm; ClientForm: TClientFormClass; App: TApplication): TClientForm;  
begin  
  Application := App;     /// HERE  
  ...  
end;  

Here you replace the Application variable with your own one that comes from the other form. As a result, after closing the project, your application is destroyed twice and the second time the AV exception is raised.

To avoid the issue, I recommend you enable runtime packages (at least  "vcl"  and "rtl" ) and comment out the following code string:

Delphi
Application := App;  

I've attached your test project containing my modifications to illustrate the issue.

Hello Mikhail,
once a module (dll) is loaded, there's no way for explicitly unloading it (by now, maybe it will be necessary later).
All loaded lbraries are unloaded when the host will be terminated.
I changed my host's form class so that at first all loaded libraries will be unloaded with FreeLibrary() and I can call the exported dxFinalize inside each library.

Maybe it's a quite strange construction, but replacing the Application variable is necessary to use the forms inside a library as a MDI-Child for the main form.

And by the way … using runtime packages is not an option ;-)

All is working quite well by now, so thank you very much for your efforts.

Kind regards
Bernd