unit Unit1;

interface

uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 Dialogs, Vcl.StdCtrls;

type
 TForm1 = class(TForm)
   edt1: TEdit;
   btn1: TButton;
   edt2: TEdit;
   btn2: TButton;
   procedure btn1Click(Sender: TObject);
   procedure btn2Click(Sender: TObject);
 private
   { Private declarations }
 public
   { Public declarations }
 end;

 Tfunc = function(n: integer): integer;

var
 Form1: TForm1;

implementation

function ShowForm: integer; external 'mylib.dll';
{$R *.dfm}

procedure TForm1.btn1Click(Sender: TObject);
var
 LibHandle: THandle;
 i: integer;
 func: Tfunc;
begin
 LibHandle := loadLibrary('mylib.dll');
 try
   if LibHandle <> 0 then
   begin

     @func := GetProcAddress(LibHandle, 'fn_calc');
     if addr(func) <> nil then
     begin
       i := strtoint(edt1.text);
       edt2.text := IntToStr(func(i));
       edt1.text := IntToStr(Random(10));
     end
     else
       ShowMessage('Функция не найдена!');
   end
   else
     ShowMessage('Библиотека не загружена!');
 finally
   FreeLibrary(LibHandle);
 end;
end;

procedure TForm1.btn2Click(Sender: TObject);
var
 LibHandle: THandle;
 i: integer;
 func: Tfunc;
begin
 LibHandle := loadLibrary('mylib.dll');

 try
   if LibHandle <> 0 then
   begin
     @func := GetProcAddress(LibHandle, 'ShowForm');
     if addr(func) <> nil then
       ShowForm
     else
       ShowMessage('Функция не найдена!');
   end
   else
     ShowMessage('Библиотека не загружена!');
 finally
   FreeLibrary(LibHandle);
 end;
end;

end.

library mylib;

{ Important note about DLL memory management: ShareMem must be the
 first unit in your library's USES clause AND your project's (select
 Project-View Source) USES clause if your DLL exports any procedures or
 functions that pass strings as parameters or function results. This
 applies to all strings passed to and from your DLL--even those that
 are nested in records and classes. ShareMem is the interface unit to
 the BORLNDMM.DLL shared memory manager, which must be deployed along
 with your DLL. To avoid using BORLNDMM.DLL, pass string information
 using PChar or ShortString parameters. }

uses
 ShareMem,
 madExcept,
 madLinkDisAsm,
 madListHardware,
 madListProcesses,
 madListModules,
 Windows,
 Dialogs,
 ActiveX,
 SysUtils,
 Classes,
 Unit2 in 'Unit2.pas' {Form2};

{$R *.res}

procedure DLLEntryPoint(Reason: Word);
begin
 if Reason = DLL_PROCESS_DETACH then
   ShowMessage('DETACH');
end;

function fn_calc(n: integer): integer;
begin
 Result := n * 256
end;

exports
 fn_calc, ShowForm;

begin
 DLLProc := @DLLEntryPoint;
 DLLEntryPoint(DLL_PROCESS_ATTACH);
end.

unit Unit2;

interface

uses
 Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
 Vcl.Controls, Vcl.Forms, Vcl.Dialogs;

type
 TForm2 = class(TForm)
   procedure FormClose(Sender: TObject; var Action: TCloseAction);
 private
   { Private declarations }
 public
   { Public declarations }
 end;

function ShowForm: integer;

var
 Form2: TForm2;

implementation

{$R *.dfm}

function ShowForm: integer;
begin
 Form2 := TForm2.Create(Application);
 Result := Form2.ShowModal;
 FreeAndNil(Form2);
end;

procedure TForm2.FormClose(Sender: TObject; var Action: TCloseAction);
begin
 CloseHandle(Form2.Handle);
 Action := cafree;
end;

end.