How to draw a custom border inside the non client area of a control with scroll bars?

Question

I have a custom control with both scroll bars enabled and I want to draw a simple red line border around the client area and the scroll bars, like in the image below. How I

Answer 1

You are trying to paint (partial) in the Nonclient Area.
You could add WS_DLGFRAME to the Params.Style and handle the message WM_NCPaint to Paint on the HDC of the window.

  TSuperList = class(TCustomControl)
  private
    procedure PaintBorder;
    procedure WMNCActivate(var Msg: TWMNCActivate); message WM_NCActivate;
    procedure WMNCPaint(var Msg: TWMNCPaint);message WM_NCPaint;
  protected
    procedure   Paint; override;
    procedure   CreateParams(var Params: TCreateParams); override;
  public
    constructor Create(AOwner: TComponent); override;
  end;

procedure TSuperList.CreateParams(var Params: TCreateParams);
begin
  inherited;
  Params.Style:=Params.Style or WS_VSCROLL or WS_HSCROLL or WS_DLGFRAME;
end;

procedure TSuperList.WMNCActivate(var Msg: TWMNCActivate);
begin
  inherited;
  PaintBorder;
end;

procedure TSuperList.WMNCPaint(var Msg: TWMNCPaint);
begin
  inherited;
  PaintBorder;
end;

procedure TSuperList.PaintBorder;
begin
  Canvas.Handle := GetWindowDC(Handle);
  Canvas.Pen.Color := clNavy;
  Canvas.Pen.Width := 2;
  Canvas.Brush.Style := bsClear;
  Canvas.Rectangle( Rect(1,1,Width,Height) );
  ReleaseDC(Handle,Canvas.Handle);
end;    

constructor TSuperList.Create(AOwner: TComponent);
begin
 inherited;
 Color:=clBlack;
 Width:=300;
 Height:=250;
end;

procedure TSuperList.Paint;
begin
 Canvas.Brush.Color:=clWhite;
 Canvas.Pen.Style := psClear;
 Canvas.Rectangle(ClientRect);
 Canvas.Pen.Style := psSolid;
 Canvas.Ellipse(0,0,20,20);
end;