unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    Msg: LongInt;
    { Private declarations }
  protected
    procedure WndProc(var Message: TMessage); override;
  public

    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  Msg := RegisterWindowMessage(wm_mymessage);
  Self.BringToFront;
end;

procedure TForm1.WndProc(var Message: TMessage);
begin
  if Message.Msg = Msg then begin
    Caption := ;
    ShowMessage(收到消息了);
  end
  else begin
    inherited;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  M: TMessage;
  B: DWord;
begin
  M.Msg := Msg;
  B := BSM_ALLCOMPONENTS;
  BroadcastSystemMessage(BSF_POSTMESSAGE, @B , M.Msg, M.WParam, M.LParam );
end;

end.