Windows 编程[21] - WM_MENUSELECT 消息与 GetMenuString 函数

提示:

1、菜单项的标识存放在 WM_MENUSELECT 消息的 lParam 参数中的低两位.

2、WM_MENUSELECT 也包括系统菜单发送的消息.

3、因为顶层菜单(File Edit Help)一般在资源文件中设同样的标识符(譬如: 65535), 所以系统会把它们的位置(或者叫顺序)当作标识; 因此执行 GetMenuString 时, 需要使用用非默认(非0)的 MF_BYPOSITION 参数.

4、因为系统菜单的标识都大于 $F000, 所以要求我们自定义的菜单标识一般要小于这个数; 在程序中我们也是根据这个道理来区别菜单来源的.

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本例效果图:

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本例使用的资源文件(TestRes.rc):

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#define IDM_New   101
#define IDM_Open  102
#define IDM_Save  103
#define IDM_Exit  104
#define IDM_Cut   201
#define IDM_Copy  202
#define IDM_Paste 203
#define IDM_About 301

MyMenu1 MENUEX DISCARDABLE
BEGIN
  POPUP "&File"        ,65535
  BEGIN
    MENUITEM "&New"    ,IDM_New
    MENUITEM "&Open"   ,IDM_Open
    MENUITEM "&Save"   ,IDM_Save
    MENUITEM SEPARATOR
    MENUITEM "E&xit"   ,IDM_Exit
  END
  POPUP "&Edit"        ,65535
  BEGIN
    MENUITEM "Cu&t"    ,IDM_Cut
    MENUITEM "&Copy"   ,IDM_Copy
    MENUITEM "&Paste"  ,IDM_Paste
  END
  POPUP "&Help"        ,65535
  BEGIN
    MENUITEM "&About"  ,IDM_About
  END
END

本例代码文件:

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program Project1;

{$R 'TestRes.res' 'TestRes.rc'}

uses
  Windows, Messages;

{收到 WM_MENUSELECT 消息时需要做的工作}
procedure OnMenuSelect(h: HWND; wParam: Integer);
var
  buf: array[0..255] of Char;
  s: string;
  w: Word;
begin
  w := LoWord(wParam);
  Str(w, s);
  case w of
    0..99        : GetMenuString(GetMenu(h), w, buf, Length(buf), MF_BYPOSITION);
    100..$F000   : GetMenuString(GetMenu(h), w, buf, Length(buf), MF_BYCOMMAND);
    $F001..$FFFF : GetMenuString(GetSystemMenu(h, False), w, buf, Length(buf), MF_BYCOMMAND);
  end;
  s := s + ' - ' + buf;
  SetWindowText(h, PChar(s));
end;

function WndProc(wnd: HWND; msg: UINT; wParam,lParam: Integer): Integer; stdcall;
begin
  Result := 0;
  case msg of
    WM_MENUSELECT : OnMenuSelect(wnd, wParam); {收到 WM_MENUSELECT 消息后调用 OnMenuSelect 过程}
    WM_DESTROY    : PostQuitMessage(0);
  else
    Result := DefWindowProc(wnd, msg, wParam, lParam);
  end;
end;

function RegMyWndClass: Boolean;
var
  cls: TWndClass;
begin
  cls.style         := CS_HREDRAW or CS_VREDRAW;
  cls.lpfnWndProc   := @WndProc;
  cls.cbClsExtra    := 0;
  cls.cbWndExtra    := 0;
  cls.hInstance     := HInstance;
  cls.hIcon         := 0;
  cls.hCursor       := LoadCursor(0, IDC_ARROW);
  cls.hbrBackground := HBRUSH(COLOR_WINDOW + 1);
  cls.lpszMenuName  := 'MyMenu1';
  cls.lpszClassName := 'MyWnd';
  Result := RegisterClass(cls) <> 0;
end;

{程序入口}
const
  tit = 'New Form';
  ws = WS_OVERLAPPEDWINDOW;
  x = 100; y = 100; w = 300; h = 180;
var
  hWnd: THandle;
  Msg : TMsg;
begin
  RegMyWndClass;
  hWnd := CreateWindow('MyWnd', tit, ws, x, y, w, h, 0, 0, HInstance, nil);
  ShowWindow(hWnd, SW_SHOWNORMAL);
  UpdateWindow(hWnd);

  while(GetMessage(Msg, 0, 0, 0)) do
  begin
    TranslateMessage(Msg);
    DispatchMessage(Msg);
  end;
end.