基本上每个消息都有一个Result，代表是否（正确）处理过了

先看消息的定义：

  TWMContextMenu = packed record
    Msg: Cardinal;
    hWnd: HWND;
    case Integer of
      0: (
        XPos: Smallint;
        YPos: Smallint);
      1: (
        Pos: TSmallPoint;
        Result: Longint);
  end;

  TWMShowWindow = packed record
    Msg: Cardinal;
    Show: BOOL;
    Status: Longint;
    Result: Longint;
  end;

  TWMSize = packed record
    Msg: Cardinal;
    SizeType: Longint; { SIZE_MAXIMIZED, SIZE_MINIMIZED, SIZE_RESTORED,
                         SIZE_MAXHIDE, SIZE_MAXSHOW }
    Width: Word;
    Height: Word;
    Result: Longint;
  end;

看这个函数，如果Result<>0，就代表处理过了，直接退出：

procedure TControl.WMContextMenu(var Message: TWMContextMenu);
var
  Pt, Temp: TPoint;
  Handled: Boolean;
  PopupMenu: TPopupMenu;
begin
  if Message.Result <> 0 then Exit;
  if csDesigning in ComponentState then
  begin
    inherited;
    Exit;
  end;

  Pt := SmallPointToPoint(Message.Pos);
  if InvalidPoint(Pt) then
    Temp := Pt
  else
  begin
    Temp := ScreenToClient(Pt);
    if not PtInRect(ClientRect, Temp) then
    begin
      inherited;
      Exit;
    end;
  end;

  Handled := False;
  DoContextPopup(Temp, Handled);
  Message.Result := Ord(Handled);
  if Handled then Exit;

  PopupMenu := GetPopupMenu;
  if (PopupMenu <> nil) and PopupMenu.AutoPopup then
  begin
    SendCancelMode(nil);
    PopupMenu.PopupComponent := Self;
    if InvalidPoint(Pt) then
      Pt := ClientToScreen(Point(0, 0));
    PopupMenu.Popup(Pt.X, Pt.Y);
    Message.Result := 1;
  end;

  if Message.Result = 0 then
    inherited;
end;