Printing With Win32 API, MSDN example gives error

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6 total messages Started by szuchymj Sun, 04 Sep 2005 00:45

#2190

Author: szuchymj
Date: Sun, 04 Sep 2005 00:45

73 lines
3828 bytes

I am trying to print using the Win32 API in Delphi. The reason being
that a user has reported problems with TPrinter printing upon switching
to a certain Lexmark printer, even though other applications print
without problems. I have been able to replicate similar behaviour in a
VMWare virtual machine using Windows SP2 and the Docucom PDF driver: my
application and a simple prototype created with TPrinter do not print,
but other applications (notepad, word, IE) print just fine.

Regardless of your opinion of the quality of Docucom PDF driver or
Lexmark printers, the problem remains that other applications are
printing fine on these devices but mine is not. I am guessing these
other applications use MFC classes, Visual Basic 6.0, or the Win32 API.
Because I am using Delphi my only option of the three is Win32 API.

So, I wrote some printing code based on the MSDN example (
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/gdi/prntspol_1wfn.asp
) for printing with the Win32 API. It prints without error on
everything except the Docucom PDF driver, for which it says code 6
"invalid handle" upon StartPage. Even though StartDoc works fine. What
is the key difference between my code, and other applications' code,
that causes the Docucom PDF driver to print without error?

procedure printingMain;
var
pd:TPrintDlg;
di:TDocInfo;
begin
//begin setup PRINTDLG structure
FillChar(pd, SizeOf(pd), 0);
pd.lStructSize := sizeof(pd);
pd.hWndOwner:=application.Handle;
pd.hDevMode := thandle(nil);
pd.hDevNames := thandle(nil);
pd.Flags := PD_RETURNDC;
pd.hwndOwner := Application.Handle;
pd.hDC := hdc(nil);
pd.nFromPage := 1;
pd.nToPage := 1;
pd.nMinPage := 1;
pd.nMaxPage := 10;
pd.nCopies := 1;
pd.hInstance := thandle(nil);
pd.lCustData := 0;
pd.lpfnPrintHook := nil;
pd.lpfnSetupHook :=  nil;
pd.lpPrintTemplateName := pchar(nil);
pd.lpSetupTemplateName := pchar(nil);
pd.hPrintTemplate := thandle(nil);
pd.hSetupTemplate := thandle(nil);
//end setup PRINTDLG structure
PrintDlg(pd);
SetAbortProc(pd.hDC, AbortProc);
//begin setup DOCINFO structure
FillChar(di, SizeOf(di), 0);
di.cbSize := sizeof(di);
di.lpszDocName := pchar('');//'Bitmap Printing Test';
di.lpszOutput := pchar('');
di.lpszDatatype := pchar('');
di.fwType := 0;
//end setup DOCINFO structure
startdoc(pd.hDC, di);
StartPage(pd.hDC);
TextOut(pd.hDC, 10, 10, pchar('test123'),length('test123'));
EndPage(pd.hDC);
EndDoc(pd.hDC);
DeleteDC(pd.hDC);
end;

function AbortProc(Prn: HDC; Error: Integer): Bool; stdcall;
begin
Application.ProcessMessages;
Result := false;
end;

Re: Printing With Win32 API, MSDN example gives error

#2191

Author: szuchymj
Date: Sun, 04 Sep 2005 01:16

29 lines
2113 bytes

Using the example at
http://community.borland.com/article/0,1410,16139,00.html I was able to
fix the problem. Here is my new code.

procedure printMain;
var
  Pd : TPrintDlg;
  DocInfo: TDocInfo;
begin
  FillChar(Pd, sizeof(Pd), 0);
  Pd.lStructSize := sizeof(Pd);
  Pd.hWndOwner := Form1.Handle;
  Pd.Flags := PD_RETURNDC;
    if PrintDlg(pd) then
    begin
    FillChar(DocInfo, sizeof(DocInfo), 0);
    DocInfo.cbSize := SizeOf(DocInfo);
    StartDoc(Pd.hDc, DocInfo);
    StartPage(Pd.hDc);
    TextOut(Pd.hDc, 100, 100, 'test123', length('test123'));
    EndPage(Pd.hDc);
    EndDoc(Pd.hDc);
    end;
end;

I do not yet know what was causing the problem in my previous code, but
on first glance it appears that a member of the DOCINFO structure or
the PRINTDLG structure was initialized to something it should not have
been.

Re: Printing With Win32 API, MSDN example gives error

#2192

Author: szuchymj
Date: Sun, 04 Sep 2005 01:30

8 lines
1783 bytes

I found the answer. Calling SetAbortProc after showing the print dialog
via PrintDlg causes an error. Call it before PrintDlg, and the error
goes away.

It is confusing because the MSDN example appears to call SetAbortProc
after the PrintDlg call. Actually there is no PrintDlg call in the MSDN
example, but it is implied that you have already gotten the printer DC
via PrintDlg or CreateDC.

Re: Printing With Win32 API, MSDN example gives error

#2193

Author: szuchymj
Date: Sun, 04 Sep 2005 01:36

2 lines
1577 bytes

Actually that is a bad idea because calling SetAbortProc before
PrintDlg renders the abort procedure useless. It never gets called.

Re: Printing With Win32 API, MSDN example gives error

#2194

Author: szuchymj
Date: Sun, 04 Sep 2005 01:49

5 lines
1651 bytes

The Real Solution To The Problem a.k.a. Why I Am An Idiot:

AbortProc is supposed to return true if you want the print job to
continue. I for some reason assumed the opposite, that it was supposed
to return false.

Re: Printing With Win32 API, MSDN example gives error

#2195

Author: Kellie Fitton
Date: Sun, 04 Sep 2005 21:33

15 lines
2236 bytes

Hi,

Before calling the API StartDoc(), the application should call the API
SetAbortProc() to set the abort procedure, then disables its own window
by using the API EnableWindow(), and displays the print-status or the
abort modeless dialogBox containing a Cancel button and some statics
controls to show the document name and the number of pages printed.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/gdi/prntspol_0883.asp

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/winui/winui/windowsuserinterface/userinput/keyboardinput/keyboardinputreference/keyboardinputfunctions/enablewindow.asp

Hope these information helps,

Kellie.

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