//例如 Panel1 无TCanvas 属性，获取TCanvas
var
  Cvs: TCanvas;
begin
  Cvs:= TCanvas.Create;
  Cvs.Handle := GetDC(Panel1.Handle);
  Cvs.Brush.Color := clBlue;
  Cvs.FillRect(Panel1.ClientRect);
  Cvs.Free;
end;