//MyInt.pas
unit MyInt;

interface

{$IFNDEF MYLIB}
function MyAdd(a,b:integer):integer ;stdcall;
{$ENDIF}

implementation

{$IFNDEF MYLIB}
function MyAdd; external 'MyLib.dll' name 'MyAdd';
{$ENDIF}
end.

//MyLib.dpr
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
  SysUtils,
  Classes,
  MyInt in 'MyInt.pas';

{$R *.res}
function MyAdd(a,b:integer):Integer ; stdcall;
begin
    result := (a + b);
end;
exports
    MyAdd;
end.

unit UnitMain;

interface

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

type
  TForm1 = class(TForm)
    btnTestDll: TButton;
    btnDynamicCall: TButton;
    procedure btnTestDllClick(Sender: TObject);
    procedure btnDynamicCallClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
type
    TFuncMyAdd = function (a,b:Integer) : integer;stdcall;

var
  Form1: TForm1;

implementation
uses
    MyInt;
{$R *.dfm}

procedure TForm1.btnTestDllClick(Sender: TObject);
begin
    ShowMessageFmt('结果＝%d',[MyAdd(1,2)]);
end;

procedure TForm1.btnDynamicCallClick(Sender: TObject);
var
    libHandle : THandle;
    funcAdd : TFuncMyAdd;
begin
   libHandle := LoadLibrary('MyLib.dll');
   try
        if libHandle = 0 then
        begin
            //raise error;
            ShowMessage('加载DLL失败!');
        end;
        @funcAdd := GetProcAddress(libHandle,'MyAdd');
        if not (@funcAdd = nil) then
        begin
            ShowMessageFmt('动态加载结果＝%d',[funcAdd(1,2)]);
        end;
   finally
     FreeLibrary(libHandle)
   end;
end;                      
end.