代码 

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->library pub_form;

uses
  SysUtils,
  Classes,
  Windows,
  Forms,
  Parameter_Object,
  frm_LoginU in '..\公用库单元\frm_LoginU.pas' {frm_Login},
  pub_Event in '..\公用库单元\pub_Event.pas',
  Dll_LIB_ConstU in '..\公用库单元\Dll_LIB_ConstU.pas';

var
  DLLApp: TApplication;

{begin-----------------------登录窗体相关-------------------------}

procedure Login(var mLoginParam: TLoginParam); export;
begin
  {获取调用窗体的Application，显而易见的功能是 能使你的窗体融合到调用程序中。通过它还能进行很多操作}
  Application := mLoginParam.App; //将DLL的Application转为App
  if frm_Login = nil then
    frm_Login := Tfrm_Login.Create(mLoginParam.ParentForm);
  frm_Login.DoLoginClick := mLoginParam.DoLogin;
  frm_Login.DoErrCatch:=mLoginParam.ErrDo;
  frm_Login.E_User.Text:=mLoginParam.OldUser;
  frm_Login.ShowModal;
end;

procedure CloseLogin; export;
begin
  if frm_Login.Showing then
    frm_Login.Close;
end;

{end-----------------------登录窗体相关-------------------------}

{重写Dll入口函数，否则程序会出错}

procedure DLLUnloadProc(Reason: Integer); register;
begin
  {DLL取消调用时，发送DLL_PROCESS_DETACH消息，此时将DLL的Application返回为本身}
  if Reason = DLL_PROCESS_DETACH then Application := DLLApp;
end;

exports
  Login,CloseLogin;

begin
  {在DLL入口预先储存DLL的Application}
  DLLApp := Application;
  {DllProc：DLL入口函数指针。Delphi定义为 DllProc: TDLLProc;}
  {在此指向我们自己定义的函数}
  DLLProc := @DLLUnloadProc;
end.

代码 

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->unit Parameter_Object;
{
调用DLL的参数对象类

}

interface
uses
  pub_Event,Forms;


type
  TDllFormParam=class(TObject)
  public
    App: TApplication;
    ParentForm:TForm;
    ErrDo:TExceptionEvent;
    constructor CreateByObject(var mApp: TApplication;var mParentForm:TForm;mErrDo:TExceptionEvent);
  end;

  TLoginParam=class(TDllFormParam)
  public
    DoLogin:TLoginClickEvent;
    OldUser:String;//上次登录的用户
    constructor CreateByObject(var mApp: TApplication;var mParentForm:TForm;mErrDo:TExceptionEvent;mDoLogin:TLoginClickEvent;mUser:string='');
  end;

implementation

{ TLoginParam }

constructor TLoginParam.CreateByObject(var mApp: TApplication;
   var mParentForm: TForm;mErrDo:TExceptionEvent; mDoLogin: TLoginClickEvent;mUser:string='');
begin
  inherited CreateByObject(mApp,mParentForm,mErrDo);
  DoLogin:=mDoLogin;
  OldUser:=mUser;
end;

{ TDllFormParam }

constructor TDllFormParam.CreateByObject(var mApp: TApplication;
  var mParentForm: TForm;mErrDo:TExceptionEvent);
begin
  App:=mApp;
  ParentForm:=mParentForm;
  ErrDo:=mErrDo;
end;
end.

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->unit pub_Event;

interface
uses
  SysUtils;

type
  //点击登录按钮时触发外部检测帐号与密码是否正确
  TLoginClickEvent = procedure(UserName, UserPW: string) of object;

implementation

end.

代码 

Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->unit frm_LoginU;

interface

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

type

  Tfrm_Login = class(TForm)
    E_User: TEdit;
    E_PassWD: TEdit;
    btn_Login: TButton;
    btn_Exit: TButton;
    procedure FormKeyPress(Sender: TObject; var Key: Char);
    procedure btn_ExitClick(Sender: TObject);
    procedure btn_LoginClick(Sender: TObject);
    procedure FormClose(Sender: TObject; var Action: TCloseAction);
  private
    { Private declarations }
  public
    { Public declarations }
    DoLoginClick: TLoginClickEvent;
    DoErrCatch:TExceptionEvent;
  end;

var
  frm_Login: Tfrm_Login;

implementation

{$R *.dfm}

procedure Tfrm_Login.FormKeyPress(Sender: TObject; var Key: Char);
begin
  if key = #13 then
  begin
    Key := #0;
    Keybd_Event(VK_TAB, 0, 0, 0);
  end;
end;

procedure Tfrm_Login.btn_ExitClick(Sender: TObject);
begin
  self.close;
end;

procedure Tfrm_Login.btn_LoginClick(Sender: TObject);
begin
  if Assigned(DoLoginClick) then
  begin
    try
    DoLoginClick(trim(E_User.Text), Trim(E_PassWD.Text));
    except   on   e:Exception   do
      DoErrCatch(sender,e);
    end;
  end;
end;

procedure Tfrm_Login.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action:=caFree;
end;

end.