Delphi detecting image type in TImageControl

Question

I am trying to detect the image type loaded in FMX's TImageControl. I am using Delphi 10.3 Rio.

My code is as follows:

function DetectImage(BM: TBitmap): string;
var
  MS: TMemoryStream;
  FirstBytes: AnsiString;
begin
  MS := TMemoryStream.Create;
  try
    BM.SaveToStream(MS);
    SetLength(FirstBytes, 8);
    MS.Read(FirstBytes[1], 8);
    if Copy(FirstBytes, 1, 2) = 'BM' then
    begin
      Result := 'bmp';
    end
    else if FirstBytes = #137'PNG'#13#10#26#10 then
    begin
      Result := 'png';
    end
    else if Copy(FirstBytes, 1, 3) = 'GIF' then
    begin
      Result := 'gif';
    end
    else if Copy(FirstBytes, 1, 2) = #$FF#$D8 then
    begin
      Result := 'jpg';
    end
    else
      Result := '?';

  finally
    MS.Free;
  end;
end;

procedure TfrmMain.imgTeamAChange(Sender: TObject);
begin
 ShowMessage(DetectImage(imgTeamA.Bitmap))  ;
end;

So, when I click on the TImageControl to change it, I always get '?' as a result.

How do I make this working?

Answer 1

Oh, I didn't know that the TImageControl has an OnLoaded event with a const FileName: string argument, that is perfect! Can't be better!