Undocumented windows message 0x0313 & TTaskBarMenu

When you right-click on a taskbar button, Windows sends an undocumented message ($0313) to the corresponding application window. The WPARAM is unused (zero) and the LPARAM contains the mouse position in screen coordinates, in the usual format. By default, WindowProc handles this message by popping up the system menu at the given coordinates.Apparently you can use it to pop up your own custom menu, but before doing that I would use e.g. Spy++ to check whether possibly it generates documented messages that can be processed instead.

 

unit TaskBarMenu;interfaceuses   SysUtils, Classes, Menus, Messages, Windows, Forms, Controls;type   TTaskBarMenu = class(TPopupMenu)   private     hookHandle : THandle;     oldWndProc: Pointer;     newWndProc: Pointer;   protected     procedure Hook;     procedure UnHook;     procedure AppWndProc(var Msg: TMessage) ;   public     constructor Create(AOwner: TComponent) ; override;     destructor Destroy; override;   end;procedure Register;implementationconst   WM_TASKBAR_MENU = $0313; // magic!   WM_POPUP_MENU = WM_USER + 1; //custom messagevar   thisOnce : TTaskBarMenu = nil;procedure Register;begin   RegisterComponents('delphi.about.com', [TTaskBarMenu]) ;end;{ TTaskBarMenu }procedure TTaskBarMenu.AppWndProc(var Msg: TMessage) ;begin   case Msg.Msg of     WM_TASKBAR_MENU: PostMessage(hookHandle, WM_POPUP_MENU, 0, 0) ;     WM_POPUP_MENU: Popup(Mouse.CursorPos.X, Mouse.CursorPos.Y) ;   else     Msg.Result := CallWindowProc(oldWndProc, hookHandle, Msg.Msg, Msg.wParam, Msg.lParam) ;   end;end; (*AppWndProc*)constructor TTaskBarMenu.Create(AOwner: TComponent) ;begin   if Assigned(thisOnce) then   begin     raise Exception.Create('Only one instance of this component can be used per application!') ;   end   else   begin     inherited;     thisOnce := self;     hookHandle := Application.Handle;     Hook;   end;end; (*Create*)destructor TTaskBarMenu.Destroy;begin   thisOnce := nil;   UnHook;   inherited;end; (*Destroy*)procedure TTaskBarMenu.Hook;begin   oldWndProc := Pointer(GetWindowLong(hookHandle, GWL_WNDPROC)) ;   newWndProc := Classes.MakeObjectInstance(AppWndProc) ;   if not (csDesigning in ComponentState) then SetWindowLong(hookHandle, GWL_WNDPROC, longint(newWndProc)) ;end; (*Hook*)procedure TTaskBarMenu.UnHook;begin   SetWindowLong(hookHandle, GWL_WNDPROC, longint(oldWndProc)) ;   if Assigned(newWndProc) then Classes.FreeObjectInstance(newWndProc) ;   NewWndProc := nil;end; (*UnHook*)end.

 

 

备注：本文参考自：

1、http://stackoverflow.com/questions/10430377/winapi-undocumented-windows-message-0x0313-stable

2、http://delphi.about.com/od/vclwriteenhance/a/ttaskbarmenu.htm