如何找到是否安装了打印机（使用Delphi）

Question

My program is written in Delphi (object oriented pascal). When I try to print anything I get the message "There is no default printer currently selected." on computers with no printers installed.

To prevent this I want to check if there are any printers installed. Is there any way to check if any printers are installed?

Answer 1

use Printers;

Printer.Printers.Count gives you the number of printers installed

The comments form the Printers unit in D2007:

  { TPrinter }

  { The printer object encapsulates the printer interface of Windows.  A print
    job is started whenever any redering is done either through a Text variable
    or the printers canvas.  This job will stay open until EndDoc is called or
    the Text variable is closed.  The title displayed in the Print Manager (and
    on network header pages) is determined by the Title property.

    EndDoc - Terminates the print job (and closes the currently open Text).
      The print job will being printing on the printer after a call to EndDoc.
    NewPage - Starts a new page and increments the PageNumber property.  The
      pen position of the Canvas is put back at (0, 0).
    Canvas - Represents the surface of the currently printing page.  Note that
      some printer do not support drawing pictures and the Draw, StretchDraw,
      and CopyRect methods might fail.
    Fonts - The list of fonts supported by the printer.  Note that TrueType
      fonts appear in this list even if the font is not supported natively on
      the printer since GDI can render them accurately for the printer.
    PageHeight - The height, in pixels, of the page.
    PageWidth - The width, in pixels, of the page.
    PageNumber - The current page number being printed.  This is incremented
      when ever the NewPage method is called.  (Note: This property can also be
      incremented when a Text variable is written, a CR is encounted on the
      last line of the page).
    PrinterIndex - Specifies which printer in the TPrinters list that is
      currently selected for printing.  Setting this property to -1 will cause
      the default printer to be selected.  If this value is changed EndDoc is
      called automatically.
    Printers - A list of the printers installed in Windows.
    Title - The title used by Windows in the Print Manager and for network
      title pages. }

Answer 2

Here is a code snippet that populates a image combo box with all the printers currently installed:

procedure TMyForm.RefreshPrinterList;
var
  I: Integer;
  NewItem: TComboExItem;
  PPrinterEnumArray, PLocator: PPrinterInfo2;
  ArraySize, BufferSize: cardinal;
  strBuffer: string;
const
  idx_Default_Net_printer = 0;
  idx_Net_printer = 1;
  idx_Default_Local_printer = 2;
  idx_Local_printer = 3;

begin
  DefaultPrinterName := getDefaultPrinterName;
  cbPrinterList.ItemsEx.Clear;
  // S.G. 4/4/2008: list all other printers
  // S.G. 4/4/2008: Get the necessary buffer size
  ArraySize := 0;
  BufferSize := 0;
  PPrinterEnumArray := nil;
  EnumPrinters(PRINTER_ENUM_LOCAL or PRINTER_ENUM_CONNECTIONS, nil, 2, nil, 0, BufferSize, ArraySize);
  PPrinterEnumArray := AllocMem(BufferSize);
  try
    if EnumPrinters(PRINTER_ENUM_LOCAL or PRINTER_ENUM_CONNECTIONS, nil, 2, PPrinterEnumArray, BufferSize, BufferSize, ArraySize) then
    begin
      PLocator := PPrinterEnumArray;
      if ArraySize > 0 then
      begin
        for I := 0 to ArraySize - 1 do    // Iterate
        begin
          NewItem := cbPrinterList.ItemsEx.Add;
          strBuffer := StrPas(PLocator^.pPrinterName);
          UniqueString(strBuffer); // make sure we have a unique string instance and not a pointer
          NewItem.Caption := strBuffer;

          if AnsiSameText(DefaultPrinterName, strBuffer) then
          begin
            // default printer
            if  (PRINTER_ATTRIBUTE_LOCAL AND PLocator^.Attributes) <> 0 then
            begin
              // Local, default printer
              NewItem.ImageIndex := idx_Default_Local_printer;
            end
            else
            begin
              // Network default printer
              NewItem.ImageIndex := idx_Default_Net_printer;
            end;
            cbPrinterList.ItemIndex := NewItem.Index;
          end
          else
          begin
            // default printer
            if  (PRINTER_ATTRIBUTE_LOCAL AND PLocator^.Attributes) <> 0 then
            begin
              // Local, default printer
              NewItem.ImageIndex := idx_Local_printer;
            end
            else
            begin
              // Network default printer
              NewItem.ImageIndex := idx_Net_printer;
            end;
          end;
          Inc(PLocator);
        end;    // for
      end;
    end;
  finally // wrap up
    FreeMem(PPrinterEnumArray);
  end;    // try/finally
end;