Delphi programming to detect the existence of printers

Printers is designed to control the printer, but when the printer is not installed, but will be prompted I/O error, so there must be a test to detect the existence of a printer, I tried many methods, but I/O error is always earlier than my judgment, so use the following bad recruit to detect the printer. You can detect the presence of a printer by first adding printers to the uses, then preparing a list box ComboBox1, its properties visible set to False, and then executing the following statements before printing:

procedure TForm1.ButtonClick(Sender: TObject);
begin
ComboBox1.Clear;
ComboBox1.Items.Assign(Printer.Printers);
if ComboBox1.Items.CommaText= then
Messagedlg(你需要安装打印机才能打印！,mtError,[mbOk],0);
else
Form1.Print;
end;