这个全局钩子为什么只能钩住本程序的消息？(100分)

{ 钩子 DLL 源代码 }

library HookDll;

{ 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,
Dllfunc in 'Dllfunc.pas';

exports
StartHook, StopHook;

{$R *.res}

begin
end.

{--------------------------------------------------------}

unit Dllfunc;

interface

uses
Windows, SysUtils, Classes, Messages;

const
WM_Main_Accept = WM_User + 1;

function StartHook(AMainWnd: HWND): Boolean; stdcall; {开始钩子}
procedure StopHook; stdcall; {停止钩子}

function HookCallWndProc(nCode: Integer; wPar: WParam; lPar: LParam): LRESULT; stdcall;
function HookCallWndProcRet(nCode: Integer; wPar: WParam; lPar: LParam): LRESULT; stdcall;
{ 钩子响应函数 }

implementation

var
MainWnd: HWND;
{ 钩子消息发往这个窗体 }

hCallWndProc: THandle;
hCallWndProcRet: THandle;
{ 钩子类型变量 }

const
MsgArea: array[0..18] of UINT =
(WM_NCPAINT, WM_NCACTIVATE, WM_CHAR,
WM_ENABLE, WM_KEYUP, WM_LBUTTONUP, WM_MBUTTONUP, WM_PALETTECHANGED,
WM_RBUTTONUP, WM_SYSCOLORCHANGE, WM_SETFOCUS, WM_HSCROLL,
WM_VSCROLL, WM_WINDOWPOSCHANGING, WM_DESTROY, WM_WINDOWPOSCHANGED, WM_PAINT,
482, 485);
{ 定义响应消息的范围 }

function InMessageArea(const Msg: UINT): Boolean;
var
i: Integer;
begin
Result := False;
for i:=Low(MsgArea) to High(MsgArea) do
if MsgArea = Msg then
begin
Result := True;
Break;
end;
end;

function HookCallWndProc(nCode: Integer; wPar: WParam; lPar: LParam): LRESULT; stdcall;
var
Cwp: TCWPStruct;
begin
if nCode = HC_ACTION then
begin
Cwp := (PCWPStruct(lPar))^;
if InMessageArea(Cwp.message) then
PostMessage(MainWnd, WM_Main_Accept, Cwp.hwnd, Cwp.message);
{ 向主窗体发送发生消息的窗口句柄 }
end;
Result := CallNextHookEx(hCallWndProc, nCode, wPar, lPar);
end;

function HookCallWndProcRet(nCode: Integer; wPar: WParam; lPar: LParam): LRESULT; stdcall;
var
CwpRet: TCWPRetStruct;
begin
if nCode = HC_ACTION then
begin
CwpRet := (PCWPRetStruct(lPar))^;
if InMessageArea(CwpRet.message) then
PostMessage(MainWnd, WM_Main_Accept, CwpRet.hwnd, CwpRet.message);
{ 向主窗体发送发生消息的窗口句柄 }
end;
Result := CallNextHookEx(hCallWndProcRet, nCode, wPar, lPar);
end;

function StartHook(AMainWnd: HWND): Boolean; stdcall;
begin
MainWnd := AMainWnd;
hCallWndProc := SetWindowsHookEx(WH_CALLWNDPROC, HookCallWndProc, HInstance, 0);
hCallWndProcRet := SetWindowsHookEx(WH_CALLWNDPROCRET, HookCallWndProcRet, HInstance, 0);
{ 钩子的目标线程是 0 ，应该对所有线程有效 }
Result := (hCallWndProc <> 0) and (hCallWndProcRet <> 0);
if not Result then StopHook;
end;

procedure StopHook; stdcall;
begin
if hCallWndProc <> 0 then UnhookWindowsHookEx(hCallWndProc);
if hCallWndProcRet <> 0 then UnhookWindowsHookEx(hCallWndProcRet);
end;

end.

{----------------------------------------------------------------}
{ 主程序源代码 }

unit Unit1;

interface

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

const
WM_Main_Accept = WM_User + 1;

type
TForm1 = class(TForm)
btnBegin: TButton;
btnStop: TButton;
mmMessage: TMemo;
procedure btnBeginClick(Sender: TObject);
procedure btnStopClick(Sender: TObject);
private
procedure WMAcceptMessage(var AMessage: TMessage); message WM_Main_Accept;
public
{ Public declarations }
end;

function StartHook(AMainWnd: HWND): Boolean; stdcall; external 'HookDll.dll';
procedure StopHook; stdcall; external 'HookDll.dll';

var
Form1: TForm1;
RecFile: TIniFile;

implementation

{$R *.dfm}

{ TForm1 }

procedure TForm1.WMAcceptMessage(var AMessage: TMessage);
var
WinText: array[0..254] of Char;
begin
GetWindowText(AMessage.WParam, WinText, 255);
RecFile.WriteString('HookRec',DateTimeToStr(Now),
WinText+' 消息值：'+IntToStr(AMessage.LParam));
{ 把发生消息的信息记录到 Ini 文件中 }
end;

procedure TForm1.btnBeginClick(Sender: TObject);
begin
StartHook(Self.Handle);
RecFile := TIniFile.Create(ExtractFilePath(Application.ExeName)+'Rec.txt');
end;

procedure TForm1.btnStopClick(Sender: TObject);
begin
RecFile.Free;
StopHook;
end;

end.

{----------------------------------------------------------}

程序运行后，只有本程序发生事件后，才响应钩子函数。
按照全局钩子的要求，我已经将钩子函数单独放到了 Dll 中，
为什么还是不能响应其它程序的消息。

不好意思,不太熟悉

为什么要用到钩子

内存共享。

WM_Main_Accept = WM_User + 1;很多人用 加多点如
WM_Main_Accept = WM_User + 3721;

dinglj1760 四个字的回答，点到了点子上。对于高手一看就知道，但对于我们菜鸟你这样的回答，未免有点不负责任！

我很偶然的从网上看到一段文字，启发了我。如下：

对于远程钩子，钩子函数必须放到DLL中，它们将从DLL中映射到其它的进程空间中去。当WINDOWS映射DLL到其它的进程空间中去时，不会把数据段也进行映射。简言之，所有的进程仅共享DLL的代码，至于数据段，每一个进程都将有其单独的拷贝。这是一个很容易被忽视的问题。您可能想当然的以为，在DLL中保存的值可以在所有映射该DLL的进程之间共享。在通常情况下，由于每一个映射该DLL的进程都有自己的数据段，所以在大多数的情况下您的程序运行得都不错。但是钩子函数却不是如此。对于钩子函数来说，要求DLL的数据段对所有的进程也必须相同。这样您就必须把数据段设成共享的。

在以上代码的钩子回调函数中用到的 MainWnd, WM_Main_Accept, MsgArea 都是在钩子 Dll 内的非共享的数据段，如果要作全局钩子，这些变量是不能直接引用的。因此必须将这些数据用共享内存的方法访问才行。

结贴