本例效果图:

代码文件:

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    Button5: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
    procedure Button5Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  protected
    procedure WMSysCommand(var Message: TWMSysCommand); message WM_SYSCOMMAND;
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{定义两个菜单命令 ID 常数, 自定义的此类常数应该小于 $F000, 因为系统使用的都大于这个数}
const
  MenuCmdID1 = 101;
  MenuCmdID2 = 102;

{添加}
procedure TForm1.Button1Click(Sender: TObject);
var
  h: HMENU;
begin
  {系统菜单句柄}
  h := GetSystemMenu(Handle, False);
  AppendMenu(h, MFT_STRING, MenuCmdID1, '新添加的菜单项');
end;

{插入}
procedure TForm1.Button2Click(Sender: TObject);
var
  h: HMENU;
begin
  h := GetSystemMenu(Handle, False);
  {这是插入在 "还原" 菜单(SC_RESTORE) 前面}
  InsertMenu(h, SC_RESTORE, MFT_STRING, MenuCmdID2, '插入的菜单项');
end;

{修改}
procedure TForm1.Button3Click(Sender: TObject);
var
  h: HMENU;
begin
  h := GetSystemMenu(Handle, False);
  ModifyMenu(h, SC_MOVE, MF_BYCOMMAND, SC_MOVE, '这是我改的');
end;

{删除}
procedure TForm1.Button4Click(Sender: TObject);
var
  h: HMENU;
begin
  h := GetSystemMenu(Handle, False);
  {这是删除的 "关闭" 菜单, 此时窗口的关闭按钮会变灰}
  DeleteMenu(h, SC_CLOSE, MF_BYCOMMAND);
end;

{恢复}
procedure TForm1.Button5Click(Sender: TObject);
begin
  GetSystemMenu(Handle, True);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Button1.Caption := '添加';
  Button2.Caption := '插入';
  Button3.Caption := '修改';
  Button4.Caption := '删除';
  Button5.Caption := '恢复';
end;

procedure TForm1.WMSysCommand(var Message: TWMSysCommand);
var
  h: HMENU;
  buf: array[Byte] of Char;
begin
  h := GetSystemMenu(Handle, False);
  case Message.CmdType of
    MenuCmdID1: begin
      GetMenuString(h, MenuCmdID1, buf, Length(buf), MF_BYCOMMAND);
      ShowMessage(buf);
    end;
    MenuCmdID2: begin
      GetMenuString(h, MenuCmdID2, buf, Length(buf), MF_BYCOMMAND);
      ShowMessage(buf);
    end;
  end;
  inherited;
end;

end.