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unit TRM_DateTimePicker;

interface

uses
  Windows, Messages, SysUtils, Classes, Controls, Forms, ComCtrls, Dialogs, ExtCtrls, CommCtrl;

type
  TTRM_DateTimePicker = class(TDateTimePicker)
  private
    { Private declarations }
    FOnMouseLeave: TNotifyEvent;
    FOnMouseEnter: TNotifyEvent;

    procedure CMMouseEnter(var msg: TMessage); message CM_MOUSEENTER;
    procedure CMMouseLeave(var msg: TMessage); message CM_MOUSELEAVE;

    procedure CNNotify(var Message: TWMNotify); message CN_NOTIFY;
  protected
    { Protected declarations }
    procedure DoMouseEnter; dynamic;
    procedure DoMouseLeave; dynamic;

    procedure DoDropDown; dynamic;
  public
    { Public declarations }
  published
    { Published declarations }
    property OnMouseEnter: TNotifyEvent read FOnMouseEnter write FOnMouseEnter;
    property OnMouseLeave: TNotifyEvent read FOnMouseLeave write FOnMouseLeave;

    property WeekNumbers;
  end;

procedure Register;

implementation

procedure Register;
begin
  RegisterComponents('TRM', [TTRM_DateTimePicker]);
end;

{ TDateTimePicker_Leave }

procedure TTRM_DateTimePicker.CMMouseEnter(var msg: TMessage);
begin
  DoMouseEnter;
end;

procedure TTRM_DateTimePicker.CMMouseLeave(var msg: TMessage);
begin
  DoMouseLeave;
end;

procedure TTRM_DateTimePicker.CNNotify(var Message: TWMNotify);
begin
  if Message.NMHdr.code = DTN_DROPDOWN then
  begin
    if Self.WeekNumbers then
      DoDropDown;
  end;
  inherited;
end;

procedure TTRM_DateTimePicker.DoMouseEnter;
begin
  if Assigned(FOnMouseEnter) then
    FOnMouseEnter(Self);
end;

procedure TTRM_DateTimePicker.DoMouseLeave;
begin
  if Assigned(FOnMouseLeave) then
    FOnMouseLeave(Self);
end;

procedure TTRM_DateTimePicker.DoDropDown;
const
  MCM_GETMAXTODAYWIDTH = MCM_FIRST + 21;
var
  Style: LongInt;
  hDTP: THandle;
  r: TRect;
  intTodayWidth: Integer;

  cname: array [0 .. 256] of Char;
begin

  inherited;

  // to get a handle of calendar
  hDTP := DateTime_GetMonthCal(Self.Handle);

  // change a style
  Style := GetWindowLong(hDTP, GWL_STYLE);
  SetWindowLong(hDTP, GWL_STYLE, Style or MCS_WEEKNUMBERS);

  // now we must change the width for calendar because week numbers shifted all strings
  // 1. to get the required rect
  r := Rect(0, 0, 0, 0);
  SendMessage(hDTP, MCM_GETMINREQRECT, 0, LongInt(@r));

  // 2. to get the maximum width of the "today" string
  intTodayWidth := SendMessage(hDTP, MCM_GETMAXTODAYWIDTH, 0, 0);

  // 3. adjust rect width to fit the "today" string
  if intTodayWidth > r.Right then
    r.Right := intTodayWidth;

  // For Win7, the window (class=SysMonthCal32) is automatically inside
  // a parent-window (class=DropDown). Check this. If so, take the parent window.
  // If not so (class=TMainForm), take this window (for XP and lower)
  GetClassName(GetParent(hDTP), cname, sizeof(cname));
  if AnsiSameText(cname, 'DropDown') then
  begin
    hDTP := GetParent(hDTP);

    // To get it perfect (on my machines) is adding this code:
    inc(r.Right, 6);
    inc(r.Bottom, 6);
  end;

  // 4. to set new the height and width
  MoveWindow(hDTP, r.Left, r.Top, r.Right - r.Left, r.Bottom - r.Top, true);

end;

end.