Delphi Check for Default Printer Failing - delphi

Question

I use the code below to prevent an exception when someone tries to print but doesn't have a default printer set. I've gotten a report from a user using the software remotely with citrix who has a network printer as the default printer. It raises an exception at the call to GetPrinter with the message "There is no default printer currently selected". They have no problems printing from other applications. What would be going wrong here?
function CheckForDefaultPrinter: boolean;
var
FDevice: PChar;
FDriver: PChar;
FPort: PChar;
FHandle: THandle;
CurrentPrinterName: string;
begin
//ensure default printer selected - bypass printer.pas bug
Printer.PrinterIndex := Printer.PrinterIndex;
GetMem (FDevice, 255);
GetMem (FDriver, 255);
GetMem (FPort, 255);
try
try
Printers.Printer.GetPrinter(FDevice, FDriver, FPort, FHandle);
except
on E:Exception do
ShowMessage(E.Message);
end;
CurrentPrinterName := FDevice;
finally
if FDevice <> nil then FreeMem (FDevice, 255);
if FDriver <> nil then FreeMem (FDriver, 255);
if FPort <> nil then FreeMem (FPort, 255);
end;
if CurrentPrinterName = '' then
begin
MessageDlg('You do not have a default printer defined.' +
#13#13 + 'Please select a printer before running a report.'+
#13#13 + 'Or the default printer name is blank. Please assign the printer a name.',
mtError,[mbOK],0);
Result:= False;
end
else
Result:= True;
end;

Answer 1

The error occurs before the code you posted can check it, because it fails during the first access to Printer.
You should use the WinAPI GetDefaultPrinter function directly instead to see if a default printer exists, before attempting to use the global Printer. Here's a sample console application (which utilizes an easier declaration of the function than the one contained in recent versions of Delphi) to demonstrate how to do so. The sample was compiled in XE 10 Seattle and tested on Windows 7 64-bit.
program Project1;
{$APPTYPE CONSOLE}
uses
System.SysUtils, WinAPI.Windows;
function GetDefaultPrinter(Buffer: PChar; var BufferSize: DWord): BOOL; stdcall;
external 'winspool.drv' name 'GetDefaultPrinterW'; // GetDefaultPrinterA on pre-Unicode Delphi versions
var
Buff: string;
BuffSize, Err: DWord;
begin
// Get size of buffer needed.
GetDefaultPrinter(nil, BuffSize);
SetLength(Buff, BuffSize);
// If this call fails, and GetLastError returns
// ERROR_FILE_NOT_FOUND, there is no default printer assigned.
if GetDefaultPrinter(PChar(Buff), BuffSize) then
WriteLn('Default printer: ', Buff)
else
begin
Err := GetLastError();
if Err = ERROR_FILE_NOT_FOUND then
WriteLn('No default printer assigned')
else
WriteLn('Failed. Error: ', Err);
end;
ReadLn;
end.
Note that the return value includes the terminating NULL (#0) according to the documentation. To remove it, simply SetLength(Buff, Length(Buff) - 1) after the call to GetDefaultPrinter returns.

Answer 2

On Windows you can assume that if there is more than 0 (zero) printers then there is a default printer.
This assmption is safe except if your application is running as a service.
So all you need is this:
if (Printer.Printers.Count=0) then
ShowMessage('Please install a printer before attempting to print.');
You need to make this check before you access most other properties/methods on the Printer object.
If your application is running as a service there will be no default printer. Here PrinterIndex will be -1 until you assign a value in code.

Answer 3

I tested your code with Delphi XE6, Win7Pro. Just changed a line
GetMem (FPort, 255);
try
try
Printer.GetPrinter(FDevice, FDriver, FPort, FHandle); // HERE
except
on E:Exception do
ShowMessage(E.Message);
end;
It works with a networked printer as default, even with cable unplugged.