Question

I’m using delphi 2010

Answer 1

I agree with Andreas and Serg in that the control is transparent when themes are enabled.

I, once, had tried to make the CheckBox transparent for when runtime themes are not enabled in project options, or a classic theme is selected with the OS; the result was not perfect. The below is the same code applied to the RadioButton.

Problems easily noticable are, as you would guess from the code, it’s a bit flickery and it is not transparent when DoubleBuffered. A problem not easily noticable can (sometimes) be duplicated by bringing a different window in front of the form containing the controls, and then slowly moving it aside, sometimes this leaves some artifacts.

Well, anyway, here it is;

type
  TMyRadioButton = class(TRadioButton)
  private
    procedure CnCtlColorStatic(var Msg: TWMCtlColorStatic); message CN_CTLCOLORSTATIC;
    procedure WmEraseBkgnd(var Msg: TWMEraseBkgnd); message WM_ERASEBKGND;
    procedure WmPaint(var Msg: TWMNCPaint); message WM_PAINT;
  protected
    procedure CreateParams(var Params: TCreateParams); override;
  end;

implementation

uses
  themes;

procedure TMyRadioButton.CreateParams(var Params: TCreateParams);
begin
  inherited CreateParams(Params);
  Params.ExStyle := Params.ExStyle or WS_EX_TRANSPARENT;
end;

procedure TMyRadioButton.WmPaint(var Msg: TWMNCPaint);
begin
  if not (ThemeServices.ThemesEnabled or DoubleBuffered) then
    InvalidateRect(Handle, nil, True);
  inherited;
end;

procedure TMyRadioButton.WmEraseBkgnd(var Msg: TWMEraseBkgnd);
var
  R: TRect;
begin
  if not (ThemeServices.ThemesEnabled or DoubleBuffered)
       and (Parent <> nil) then begin
    R := Rect(Left, Top, Left + Width, Height + Top);
    InvalidateRect(Parent.Handle, @R, True);
    UpdateWindow(Parent.Handle);
    Msg.Result := 1;
  end else
    inherited;
end;

procedure TMyRadioButton.CnCtlColorStatic(var Msg: TWMCtlColorStatic);
begin
  if not (ThemeServices.ThemesEnabled or DoubleBuffered) then begin
    SetBKMode(Msg.ChildDC, TRANSPARENT);
    Msg.Result := GetStockObject(NULL_BRUSH);
  end else
    inherited;
end;