How to load an icon from resources to a TImage?

Question

I try the following code and it's not working... LoadIconWithScaleDown returns a negative error code.

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Image1: TImage;
    procedure FormCreate(Sender: TObject);
    procedure LoadResToImg(RID: String; const Img: TImage);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}
{$R UserResources.res}

uses Winapi.CommCtrl;

procedure TForm1.LoadResToImg(RID: String; const Img: TImage);
var Ico: TIcon;
    hI: HICON;
    HR: HResult;
begin
 Ico:= TIcon.Create;
 HR:= LoadIconWithScaleDown(HInstance, PChar(RID), Img.Width, Img.Height, hI);
 Ico.Handle:= hI;
 Img.Picture.Bitmap.Assign(Ico);
 Ico.Free;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
 LoadResToImg('OFFLINE', Image1);
end;

end.

UserResources.rc

OFFLINE      ICON    "gray_button.ico"
ONLINE       ICON    "green_button.ico" 

Answer 1

This is probably because the VCL's wrapper (in Winapi.CommCtrl.pas) for this Win32 function is faulty, or at least cannot be used straight away.

So instead declare it yourself:

function LoadIconWithScaleDown(hinst: HINST; pszName: LPCWSTR; cx: Integer;
    cy: Integer; var phico: HICON): HResult; stdcall; external 'ComCtl32';

But beware that this function is only present on Windows Vista+ (IIRC).