如何从TDateTimePicker的MonthCalendar子级接收MCN\u VIEWCHANGE通知?

嗯,结果比预期的容易多了。我的印象是 MCN_VIEWCHANGE 通知被发送到子句柄的wndproc。相反,它被发送到DateTimePicker wndproc,但是使用MonthCalender子级的窗口句柄(这就是为什么我在第一次尝试中没有捕捉到它)。因此,对该通知实施适当的处理结果是直截了当的。下面是我在Delphi中扩展内置 TDateTimePicker

const
  MCN_VIEWCHANGE = MCN_FIRST - 4; // -750

type
  tagNMVIEWCHANGE = record
    nmhdr: TNmHdr;
    dwOldView: DWORD;
    dwNewView: DWORD;
  end;
  PNMNMVIEWCHANGE = ^TNMNMVIEWCHANGE;
  TNMNMVIEWCHANGE = tagNMVIEWCHANGE;

type
  {$SCOPEDENUMS ON}
  TViewKind = (Month, Year, Decade, Century);
  {$SCOPEDENUMS OFF}

  TViewChange = procedure(Sender: TObject; OldView, NewView: TViewKind) of object;

type
  TDateTimePicker = class(Vcl.ComCtrls.TDateTimePicker)
  private
    FOnViewChange: TViewChange;
    procedure WMNotify(var Message: TWMNotify); message WM_NOTIFY;
  protected
    procedure ViewChange(OldView, NewView: TViewKind);
  public
  published
    property OnViewChange: TViewChange read FOnViewChange write FOnViewChange;
  end;

procedure TDateTimePicker.ViewChange(OldView, NewView: TViewKind);
begin
  if Assigned(FOnViewChange) then FOnViewChange(Self, OldView, NewView);
end;

procedure TDateTimePicker.WMNotify(var Message: TWMNotify);
var
  vwchg: PNMNMVIEWCHANGE;
begin
  if Message.Msg = WM_NOTIFY then begin
    vwchg := PNMNMVIEWCHANGE(Message.NMHdr);
    if vwchg.nmhdr.code = MCN_VIEWCHANGE then begin
      ViewChange(TViewKind(vwchg.dwOldView), TViewKind(vwchg.dwNewView));
    end;
  end;
  inherited;
end;