Interface DLL form app crashing - delphi

Question

I have problem with host application, which loads DLL form and interfaceing some function and properties.
The purpose is load a dll, show name as module name, set connection to ADOTable component and show form with data. Everything is working fine. But after close the host app a host app crashed and I get windows that hostapp.exe stopped working.
I do not know whether it is by freeing library or setting nil for interface.
Do you have any solution? Thanks.
Interface CODE
unit u_baseplugin_intf;
interface
uses Data.Win.ADODB, Data.DB;
type
IBaseModuleInterface = interface
['{060A9C46-B3CF-4BA4-B025-2DC1D9F45076}']
function GetModuleName: Ansistring;stdcall;
procedure SetConn(sConn:TAdoConnection);stdcall;
procedure showF;stdcall;
procedure freeF;stdcall;
property ModuleName: Ansistring read GetModuleName;
property Connection : TAdoConnection write SetConn;
end;
implementation
end.
DLL code
library profileslist;
uses
System.SysUtils,
System.Classes,
u_baseplugin_intf,
u_profileslist in 'u_profileslist.pas' {Form_DLL};
{$R *.res}
function LoadModule:IBaseModuleInterface;stdcall;
begin
result:=TForm_DLL.Create(nil);
end;
exports
LoadModule;
begin
end.
DLL Form code
unit u_profileslist;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.Grids, Vcl.DBGrids, Vcl.StdCtrls,
u_baseplugin_intf, Data.DB,Data.Win.ADODB;
type
TForm_DLL = class(TForm, IBaseModuleInterface)
DBGrid1: TDBGrid;
ADOTable1: TADOTable;
DataSource1: TDataSource;
procedure FormShow(Sender: TObject);
procedure FormClose(Sender: TObject; var Action: TCloseAction);
private
{ Private declarations }
{Interface methods implementation}
function GetModuleName: AnsiString;stdcall;
procedure SetConn(sConn:TAdoConnection);stdcall;
public
{ Public declarations }
{Interface methods implementation}
procedure ShowF;stdcall;
procedure FreeF;stdcall;
end;
var
Form_DLL: TForm_DLL;
implementation
{$R *.dfm}
{Interface methods implementation}
function TForm_DLL.GetModuleName;
begin
Result := 'Profiles list';
end;
procedure TForm_DLL.SetConn(sConn: TAdoConnection);
begin
AdoTable1.Connection:=sConn;
end;
procedure TForm_DLL.ShowF;
begin
ShowModal;
end;
procedure TForm_DLL.FreeF;
begin
FreeAndNil(Form_DLL);
end;
{Form_DLL methods implementation}
procedure TForm_DLL.FormClose(Sender: TObject; var Action: TCloseAction);
begin
AdoTable1.Active:=false;
end;
procedure TForm_DLL.FormShow(Sender: TObject);
begin
AdoTable1.Active:=true;
end;
end.
HOST app code
program hostapp;
uses
Vcl.Forms,
u_hostapp in 'u_hostapp.pas' {Form1},
u_baseplugin_intf in 'u_baseplugin_intf.pas';
{$R *.res}
begin
Application.Initialize;
Application.MainFormOnTaskbar := True;
Application.CreateForm(TForm1, Form1);
Application.Run;
end.
Host app FORM code
unit u_hostapp;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Vcl.ExtCtrls,
u_baseplugin_intf,
Data.Win.ADODB, Data.DB;
type
TForm1 = class(TForm)
ADOConnection1: TADOConnection;
Button1: TButton;
Label1: TLabel;
procedure Button1Click(Sender: TObject);
procedure FormClose(Sender: TObject; var Action: TCloseAction);
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
type
TModuleInterface = function:IBaseModuleInterface; stdcall;
var
Form1: TForm1;
implementation
{$R *.dfm}
var
aModuleIntf : IBaseModuleInterface;
dllHandle : cardinal;
procedure LoadModule( aLibName : pWideChar );
var
lModule : TModuleInterface;
begin
dllHandle := LoadLibrary(aLibName) ;
if dllHandle <> 0 then
begin
#lModule := GetProcAddress(dllHandle, 'LoadModule') ;
if Assigned (lModule) then
aModuleIntf := lModule //call the function
else
begin
ShowMessage('GetModuleIntf not found.') ;
FreeLibrary(dllHandle) ;
end;
end
else
begin
ShowMessage(aLibName+' not found.') ;
end;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
aModuleIntf.Connection:=AdoConnection1;
aModuleIntf.ShowF;
end;
procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
begin
aModuleIntf.Connection:=nil;
aModuleIntf.freeF;
aModuleIntf:=nil;
FreeLibrary(dllHandle);
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
LoadModule('profileslist.dll');
Label1.Caption:=aModuleIntf.ModuleName;
end;
end.

Answer 1

You never assign to Form_DLL. This means that when you call FreeF, you then perform FreeAndNil(Form_DLL). Since Form_DLL is nil, this does nothing, and the form still exists.
Fix that by changing LoadModule:
function LoadModule:IBaseModuleInterface;stdcall;
begin
Assert(not Assigned(Form_DLL));
Form_DLL:=TForm_DLL.Create(nil);
result:=Form_DLL;
end;
Although, I'd probably change the design completely by removing Form_DLL altogether. The host app maintains a reference to the form, on which the call to Free can be made. In other words, remove Form_DLL and implement FreeF like this:
procedure TForm_DLL.FreeF;
begin
Free; // or Destroy
end;
Or even better, use reference counted interfaces on the implementing object and let aModuleIntf:=nil take the form down.