接着线程级那些代码来做，上程序只有在本程序内按字母Ａ才会发声，只为是线程级的，现在做的是系统级，只要按上钩子，无论在哪按Ａ都会发声

分两步:
一、建立 DLL, 并在 DLL 实现钩子的设置、释放和钩子函数;
二、再建一个工程调用测试.
      先写个dll
library key_a;
uses
  SysUtils,
   Windows,
  messages,
  Classes;

{$R *.res}
var
hok:hhook;
function keyb(ncode:integer;wparam:wparam;lparam:lparam):lresult;stdcall;
 begin
 if wparam=65 then
       messagebeep(0);//按Ａ发声
 result:=callnexthookex(hok,ncode,wparam,lparam);
 end;
procedure sethok;stdcall;
    begin
    hok:=setwindowshookex(wh_keyboard,@keyb,hinstance,0);
    end;
procedure unhok;stdcall;
   begin
   unhookwindowshookex(hok);
   end;

exports
sethok,unhok;

begin
end.
按Ctrl+F9 编译，生成key_a.dll


调用key_a.dll文件
新建窗体，加两个button,一个用来安装，另个用来卸载
unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
 procedure sethok;stdcall;external 'key_a.dll';
 procedure unhok;stdcall;external 'key_a.dll';

procedure TForm1.Button1Click(Sender: TObject);
begin
  sethok;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
unhok;
end;

end.

上面调用是静态调用，下面说动态调用
主是要用ＡＰＩ来动态调用
unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
{要先要定义和 DLL 中同样参数和返回值的的过程类型 ，
万一前辈用的函数类型}
type
tfun=procedure;stdcall;
var
had:thandle;
sethok,unhok:tfun;

procedure TForm1.Button1Click(Sender: TObject);
begin
had:=loadlibrary('key_a.dll');
sethok:=getprocaddress(had,'sethok');
unhok:=getprocaddress(had,'unhok');
sethok;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
unhok;
FreeLibrary(had);
end;

end.