const
  WM_5001=WM_USER+5001;
  WM_5002=WM_USER+5002;
  WM_5003=WM_USER+5003;
  WM_6001=WM_USER+6001;

type

  //自定义消息结构
  PMsgRec = ^TMsgRec;
  TMsgRec = record
    msgNo   : Cardinal;
    msgText: string;
  end;

//自定义消息接收类
  TMsgAccepter=class
  private
    procedure Msg5001Accepter(var msg:TMsgRec); message WM_5001;

  public
    procedure defaultHandler(var message); override;

  end;

implementation
uses
  Main;

{ TMsgAccepter }
procedure TMsgAccepter.Msg5001Accepter(var msg: TMsgRec);
begin
    FrmMain.Memo1.Lines.Add('接收类已收到5001消息，并对其进行了处理！')
end;

procedure TMsgAccepter.defaultHandler(var message);
var
  theMsg:TMsgRec;
begin
  theMsg:=TMsgRec(message);
  FrmMain.Memo1.Lines.Add('接收类收到消息请求，但该消息号无指定处理函数！消息号为：'+IntToStr(theMsg.msgNo));
end;

var
  theMsg:TMsgRec;
begin
  theMsg.msgNo:=WM_5001;
  theMsg.msgText:='';
  theMsgAccepter.Dispatch(theMsg);
end;

var
  theMsg:TMsgRec;
begin
  theMsg.msgNo:=WM_6001;
  theMsg.msgText:='';
  theMsgAccepter.Dispatch(theMsg);
end;

  TFrmMsgProcess = class(TForm)
    Memo1: TMemo;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
    procedure Msg5002Accepter(var msg:TMessage); message WM_5002;
    procedure Msg5003Accepter(var msg:TMessage); message WM_5003;
  public
    { Public declarations }
  end;

var
  FrmMsgProcess: TFrmMsgProcess;

implementation
uses
  Main;

{$R *.dfm}

{ TFrmMsgProcess }

procedure TFrmMsgProcess.Msg5002Accepter(var msg:TMessage);
var
  pTheMsg:PMsgRec;
begin
   Self.Memo1.Lines.Add('窗口已收到5002号消息，并开始进行处理。。。');

   Self.Memo1.Lines.Add('窗口收到的字符串参数信息为：'+String(msg.WParam));
   pTheMsg:=PMsgRec(msg.LParam);
   Self.Memo1.Lines.Add('窗口收到的结构体参数信息为：'+pTheMsg.msgText);
   
   Self.Memo1.Lines.Add('窗口对5002号消息的处理已完成！');
end;

procedure TFrmMsgProcess.FormCreate(Sender: TObject);
begin
   self.Memo1.Color:=clblack;
   self.Memo1.Font.Color:=clgreen;
end;

procedure TFrmMsgProcess.Msg5003Accepter(var msg: TMessage);
begin
   FrmMain.Memo1.Lines.Add('窗口已收到5003号消息，并开始进行处理。。。');
   Sleep(1000);
   FrmMain.Memo1.Lines.Add('窗口对5003号消息的处理已完成！');
end;

begin
  Self.Memo1.Lines.Add('主线程向子窗口发送5003号消息。。。');

  PostMessage(FrmMsgProcess.Handle,WM_5003,0,0);

  Self.Memo1.Lines.Add('主线程消息发送函数已结束！');
end;

begin
  Self.Memo1.Lines.Add('主线程向子窗口发送5003号消息。。。');

  SendMessage(FrmMsgProcess.Handle,WM_5003,0,0);

  Self.Memo1.Lines.Add('主线程消息发送函数已结束！');
end;

var
  msgStr:string;
  theMsg:TMsgRec;
begin
  msgStr:='WM_5002消息的字符串说明';
  theMsg.msgNo:=WM_5002;
  theMsg.msgText:='WM_5002消息的结构体说明';
  SendMessage(FrmMsgProcess.Handle,WM_5002,WParam(PChar(msgStr)),LParam(@theMsg));
end;