有关自定义消息广播 SendMessage(HWND_BROADCAST,WM_MyMsg,0,0);

来源：http://www.delphibbs.com/delphibbs/dispq.asp?lid=2322837

自定义一个消息  有一个程序发送给所有程序。。
所有的已运行的该程序可以相应这个消息。。。
但为什么我写的这段不好使啊。。。自己不能响应自己的消息？？？
初次尝试  请执教
分不够可以加
unit Unit1;
interface
uses Windows,Messages,Classes,Forms, StdCtrls, Controls;
const  WM_MyMsg=Wm_User+100;
type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  public
  Procedure MsgRev(var msg:TMessage);message WM_MyMsg;
  end;
var
  Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
  SendMessage(HWND_BROADCAST,WM_MyMsg,0,0);
end;
Procedure TForm1.MsgRev(var msg:TMessage);
Begin
Form1.Caption:='已运行了一个';
End;
end.

答案：

unit Unit1;
interface
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
const
  MyMessage = 'MyMessage';
type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
    FMyMsg: UINT;
  protected
    procedure WndProc(var Message: TMessage); override;
  public
    { Public declarations }
  end;
var
  Form1: TForm1;
implementation
{$R *.dfm}
procedure TForm1.Button1Click(Sender: TObject);
begin
  SendMessage(HWND_BROADCAST, FMyMsg, 0, 0);
end;
procedure TForm1.WndProc(var Message: TMessage);
begin
  inherited WndProc(Message);
  if (FMyMsg > 0) and (Message.Msg = FMyMsg) then
  Form1.Caption:='已运行了一个';
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
  FMyMsg := RegisterWindowMessage(MyMessage);
end;
end.