Question

A TDateTime picker is a ComboBox where the drop-down list is replaced with a calendar.
I use XE2 VCL Styles and changing style does’nt affect TDateTimePicker Color & Font Color.
I have change the Calendar style with this question but the solution is not OK for the ComboBox, any idea ?
Now I plan to inherit a TComboBox for use with a TMonthCalendar but I would know if anybody had a better solution.

Answer 1

In order to use the workaround of the CalColors property, you must disable the Windows Theme in the drop down window of the TDateTimePicker component, for that you must use the
DTM_GETMONTHCAL message to get the window handle.

Check this sample App

unit Unit15;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ImgList, Vcl.StdCtrls, Vcl.ComCtrls;

type
  TForm15 = class(TForm)
    DateTimePicker1: TDateTimePicker;
    procedure DateTimePicker1DropDown(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form15: TForm15;

implementation


{$R *.dfm}

uses
  Winapi.CommCtrl,
  Vcl.Styles,
  Vcl.Themes,
  uxTheme;

Procedure SetVclStylesColorsCalendar( DateTimePicker: TDateTimePicker);
Var
  LTextColor, LBackColor : TColor;
begin
   uxTheme.SetWindowTheme(DateTimePicker.Handle, '', '');//disable themes in the calendar
   //get the vcl styles colors
   LTextColor:=StyleServices.GetSystemColor(clWindowText);
   LBackColor:=StyleServices.GetSystemColor(clWindow);

   DateTimePicker.Color:=LBackColor;
   //set the colors of the calendar
   DateTimePicker.CalColors.BackColor:=LBackColor;
   DateTimePicker.CalColors.MonthBackColor:=LBackColor;
   DateTimePicker.CalColors.TextColor:=LTextColor;
   DateTimePicker.CalColors.TitleBackColor:=LBackColor;
   DateTimePicker.CalColors.TitleTextColor:=LTextColor;
   DateTimePicker.CalColors.TrailingTextColor:=LTextColor;
end;


procedure TForm15.DateTimePicker1DropDown(Sender: TObject);
var
  hwnd: WinAPi.Windows.HWND;
begin
  hwnd := SendMessage(TDateTimePicker(Sender).Handle, DTM_GETMONTHCAL, 0,0);
  uxTheme.SetWindowTheme(hwnd, '', '');//disable themes in the drop down window
end;

procedure TForm15.FormCreate(Sender: TObject);
begin
  SetVclStylesColorsCalendar( DateTimePicker1);
end;

end.

UPDATE 1

Change the background color of the “combobox” of the TDateTimePicker is a task limited by windows itself, because between others factors

1. This control doesn’t have the owner drawn capacity,
2. And if you try using the SetBkColor function has not effect in this control because the WM_CTLCOLOREDIT message is not handled by this control.

So a possible solution is intercept the WM_PAINT and WM_ERASEBKGND messages and wrote your own code to paint the control. When you uses the Vcl Styles you can use a Style hook to handle these messages.

Check this code (only as a proof of concept)

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ImgList, Vcl.StdCtrls, Vcl.ComCtrls;

type
  TForm15 = class(TForm)
    DateTimePicker1: TDateTimePicker;
    DateTimePicker2: TDateTimePicker;
    procedure DateTimePicker1DropDown(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  end;


var
  Form15: TForm15;

implementation


{$R *.dfm}

uses
  Winapi.CommCtrl,
  Vcl.Styles,
  Vcl.Themes,
  Winapi.uxTheme;

type
 TDateTimePickerStyleHookFix= class(TDateTimePickerStyleHook)
 private
    procedure WMPaint(var Message: TMessage); message WM_PAINT;
    procedure PaintBackground(Canvas: TCanvas); override;
 public
    constructor Create(AControl: TWinControl); override;
 end;

 TDateTimePickerStyleHookHelper = class helper for TDateTimePickerStyleHook
 public
    function GetButtonRect_: TRect;
 end;


Procedure SetVclStylesColorsCalendar( DateTimePicker: TDateTimePicker);
Var
  LTextColor, LBackColor : TColor;
begin
   Winapi.uxTheme.SetWindowTheme(DateTimePicker.Handle, '', '');//disable themes in the calendar
   //get the vcl styles colors
   LTextColor:=StyleServices.GetSystemColor(clWindowText);
   LBackColor:=StyleServices.GetSystemColor(clWindow);

   DateTimePicker.Color:=LBackColor;
   //set the colors of the calendar
   DateTimePicker.CalColors.BackColor:=LBackColor;
   DateTimePicker.CalColors.MonthBackColor:=LBackColor;
   DateTimePicker.CalColors.TextColor:=LTextColor;
   DateTimePicker.CalColors.TitleBackColor:=LBackColor;
   DateTimePicker.CalColors.TitleTextColor:=LTextColor;
   DateTimePicker.CalColors.TrailingTextColor:=LTextColor;
end;


procedure TForm15.DateTimePicker1DropDown(Sender: TObject);
var
  hwnd: WinAPi.Windows.HWND;
begin
  hwnd := SendMessage(TDateTimePicker(Sender).Handle, DTM_GETMONTHCAL, 0,0);
  Winapi.uxTheme.SetWindowTheme(hwnd, '', '');//disable themes in the drop down window
end;

procedure TForm15.FormCreate(Sender: TObject);
begin
  //set the colors for the TDateTimePicker
  SetVclStylesColorsCalendar( DateTimePicker1);
  SetVclStylesColorsCalendar( DateTimePicker2);
end;


{ TDateTimePickerStyleHookHelper }
function TDateTimePickerStyleHookHelper.GetButtonRect_: TRect;
begin
 Result:=Self.GetButtonRect;
end;

{ TDateTimePickerStyleHookFix }
constructor TDateTimePickerStyleHookFix.Create(AControl: TWinControl);
begin
  inherited;
  OverrideEraseBkgnd:=True;//this indicates which this style hook will call the PaintBackground method when the WM_ERASEBKGND message is sent.
end;

procedure TDateTimePickerStyleHookFix.PaintBackground(Canvas: TCanvas);
begin
  //use the proper style color to paint the background
  Canvas.Brush.Color := StyleServices.GetStyleColor(scEdit);
  Canvas.FillRect(Control.ClientRect);
end;

procedure TDateTimePickerStyleHookFix.WMPaint(var Message: TMessage);
var
  DC: HDC;
  LCanvas: TCanvas;
  LPaintStruct: TPaintStruct;
  LRect: TRect;
  LDetails: TThemedElementDetails;
  sDateTime  : string;
begin
  DC := Message.WParam;
  LCanvas := TCanvas.Create;
  try
    if DC <> 0 then
      LCanvas.Handle := DC
    else
      LCanvas.Handle := BeginPaint(Control.Handle, LPaintStruct);
    if TStyleManager.SystemStyle.Enabled then
    begin
      PaintNC(LCanvas);
      Paint(LCanvas);
    end;
    if DateMode = dmUpDown then
      LRect := Rect(2, 2, Control.Width - 2, Control.Height - 2)
    else
      LRect := Rect(2, 2, GetButtonRect_.Left, Control.Height - 2);
    if ShowCheckBox then LRect.Left := LRect.Height + 2;
    IntersectClipRect(LCanvas.Handle, LRect.Left, LRect.Top, LRect.Right, LRect.Bottom);
    Message.wParam := WPARAM(LCanvas.Handle);

    //only works for DateFormat = dfShort
    case TDateTimePicker(Control).Kind of
     dtkDate : sDateTime:=DateToStr(TDateTimePicker(Control).DateTime);
     dtkTime : sDateTime:=TimeToStr(TDateTimePicker(Control).DateTime);
    end;

    //draw the current date/time value
    LDetails := StyleServices.GetElementDetails(teEditTextNormal);
    DrawControlText(LCanvas, LDetails, sDateTime, LRect, DT_VCENTER or DT_LEFT);

    if not TStyleManager.SystemStyle.Enabled then
      Paint(LCanvas);
    Message.WParam := DC;
    if DC = 0 then
      EndPaint(Control.Handle, LPaintStruct);
  finally
    LCanvas.Handle := 0;
    LCanvas.Free;
  end;
  Handled := True;
end;


initialization
  TStyleManager.Engine.RegisterStyleHook(TDateTimePicker, TDateTimePickerStyleHookFix);

end.

Note: This style hook doesn’t draw the focused (selected) elements in the Inner text control (combobox) of the TDateTimePicker, i let this task for you.

UPDATE 2

I just wrote a vcl style hook which includes all the logic to apply the vcl style properly to the TDateTimePicker component, without use the OnDropDown event or the OnCreate event of the form. You can find the vcl style hook here (as part of the vcl styles utils project)

To use it you must add the Vcl.Styles.DateTimePickers unit to your project and register the hook in this way.

  TStyleManager.Engine.RegisterStyleHook(TDateTimePicker, TDateTimePickerStyleHookFix);