Teleprinter type printing Delphi reveals its heritage from the 1970's and
earlier when console and line printers were standard.
A D V E R T I S E M E N T
The
AssignPrn
command allows you to use the
Write and
WriteLn
commands to write a stream of text to your printer. It is simply that. There is
no control of font, of page throws, page numbering and so on. And of course, no
graphics.
Full control printingDelphi does provide modern full text and graphics
printing. The Delphi print model is very different from that of Java, where Java
asks the application for pages it chooses. In Delphi, we interrogate the print
dialog, and determine ourselves what pages are to be printed, and in what
sequence.
There are in fact two Printer objects, depending on whether you have a CLX or
VCL application. The differences are minor.
Using the printer dialogIt is highly recommended that you display the
printer dialog so that the user can control printing. In the example program
that we will build up during this tutorial, we will show a print dialog that
allows the user to select all pages, or a range of pages. We keep things as
simple as possible by ignoring the Collate option. Unfortunately, when
the user selects multiple copies, we cannot switch off the collate option, so
you should code for it in your application.
const
TOTAL_PAGES = 4;// How many pages to
print var
printDialog:
TPrintDialog;
begin
// Create a printer selection dialog
printDialog := TPrintDialog.Create(Form1);
// Set up print dialog options
printDialog.MinPage := 1; //
First allowed page number
printDialog.MaxPage := TOTAL_PAGES; //
Highest allowed page number
printDialog.ToPage:= TOTAL_PAGES; // 1 to
ToPage page range allowed
printDialog.Options := [poPageNums];//
Allow page range selection
// if the user has selected a printer
(or default), then print! if printDialog.Execute then begin
... Your print statements end; end;
Here we have created a print dialog object, set up some options, and then
displayed it. The Execute method returns true if the user has hit
OK rather than cancel. We then print the document. The user can select, via
these options, whether to print all 4 pages or a range of these pages, as seen
in a portion of the dialog shown below:
Starting to printThe
Printer object
is permanently available to your code (you must use the Printers unit to
get access to its methods and fields though). With this object, printing
proceeds in an orderly fashion.
// Use the Printer function to get
access to the global TPrinter object.
// Set to landscape orientation
Printer.Orientation := poLandscape;
// Set the printjob title - as it it appears in
the print job manager
Printer.Title := 'Test print for Delphi';
// Set the number of copies to print each page
// This is crude - it doies not take Collation
into account
Printer.Copies := printDialog.Copies;
// Start printing
Printer.BeginDoc;
This starts a print job, with a landscape page layout, and a title, and the user
specified number of copies. Note that we are ignoring collation - we always
print all page 1 copies before page 2 etc.
Responding to the dialog settingsThe following code snippet defines some
new variables :
var
page, startPage, endPage : Integer;
And we now set these variables from the print dialog:
// Has the user selected a page
range? if printDialog.PrintRange = prPageNums
then begin
startPage := printDialog.FromPage;
endPage := printDialog.ToPage;
end else // All pages begin
startPage := 1;
endPage := TOTAL_PAGES; end;
// Set up the start page number
page := startPage;
The prPageNums value is a TPrintRange value, and is one of the values
that PrintRange may have. If set, it means that the user has selected a range of
pages. The FromPage and ToPage values will then be set to the user
specified values.
The main printing logicThe following code snippet shows the main part of
our printing code:
// Keep printing whilst all OK while (not Printer.Aborted) and Printer.Printing do begin
// Show a message saying we are starting a
page
ShowMessagePos('Starting to print page '+IntToStr(page),300,300);
// Set up a medium sized font
Printer.Canvas.Font.Size := 10;
// Allow Windows to keep processing messages
Application.ProcessMessages;
// Write out the page number
Printer.Canvas.Font.Color := clBlue;
Printer.Canvas.TextOut(40,20, 'Page
number = '+IntToStr(page));
// Underline this page number
Printer.Canvas.MoveTo(40,80);
Printer.Canvas.LineTo(Printer.PageWidth-20,80);
// Now start a new page - if not the
last if (page <= endPage) and (not Printer.Aborted) then Printer.NewPage; end;
// Finish printing
Printer.EndDoc;
The functions highlighted in red illustrate printing graphics and text
operations. We have drawn a line across the page after moving the line start
point to the appropriate position. And we have written out the page number and
size values. Text is also positioned by graphical coordinate.
Both graphical and textual operations are performed on the Printer Canvas. This
is very important. It allows you to have a very similar or identical block of
code that displays to a form canvas as it does to a printer canvas. This lets
you print what you display.
Notice that we handle the page numbering, and page throws (Printer.NewPage)
ourselves.
Finally, when all pages have been printed, the last page throw is performed
when we close the print job using Printer.EndDoc.
We are not done thereIn practice, you may print documents greater in
complexity and size than this simple one. It may be important to you to provide
a print cancel mechanism, so that the user can easily abandon unwanted print
runs. However, we cannot just display a cancel dialog, since this will hold up
our processing. We must display this dialog in a separate threa of execution.
Threading is somewhat beyond the remit of this article, but is included in the
final, complete code given below. You can copy and paste this code into Delphi,
as long as you follow the instructions at the top of the code:
//
Full Unit code. //
----------------------------------------------------------- // You must
store this code in a unit called Unit1 with a form // called
Form1 that has an OnCreate event called FormCreate.
unit Unit1;
interface
uses
Printers, // Unit containing the Printer
command
SysUtils, Graphics, Windows,
Forms, Dialogs;
type
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject); end;
var
Form1: TForm1;
implementation {$R *.dfm} // Include form definitions
// A
subroutine used to display a print-cancel dialog procedure CancelDialog; begin
// Display the cancel print dialog
Dialogs.MessageDlg('Press cancel to abort
printing',mtCustom,[mbCancel],0);
// Now that the user has pressed cancel, we
abort the printing if Printer.Printing then begin
Printer.Abort;
ShowMessage('Printing aborted'); end;
// End this thread
endThread(0); end;
// The main
form On Create routine - our main program procedure TForm1.FormCreate(Sender: TObject); const
TOTAL_PAGES = 4;// How many pages to
print var
printDialog: TPrintDialog;
cancelThreadId : Integer;
threadId : LongWord;
page, startPage, endPage : Integer;
begin
// Create a printer selection dialog
printDialog := TPrintDialog.Create(Form1);
// Set up print dialog options
printDialog.MinPage := 1; //
First allowed page number
printDialog.MaxPage := TOTAL_PAGES; //
Highest allowed page number
printDialog.ToPage:= TOTAL_PAGES; // 1 to
ToPage page range allowed
printDialog.Options := [poPageNums];//
Allow page range selection
// if the user has selected a printer
(or default), then print! if printDialog.Execute then begin
// Start a cancel print dilaog as a separate
thread!
cancelThreadId := beginThread(nil,
0,
Addr(CancelDialog),
nil,
0,
threadId);
// Use the Printer function to get access to
the global TPrinter object.
// Set to landscape orientation
Printer.Orientation := poLandscape;
// Set the printjob title - as it it appears
in the print job manager
Printer.Title := 'Test print for Delphi';
// Set the number of copies to print each
page
// This is crude - it doies not take
Collation into account
Printer.Copies := printDialog.Copies;
// Start printing
Printer.BeginDoc;
// Has the user selected a page range? if printDialog.PrintRange = prPageNums then begin
startPage := printDialog.FromPage;
endPage := printDialog.ToPage;
end else // All pages begin
startPage := 1;
endPage := TOTAL_PAGES; end;
// Set up the start page number
page := startPage;
// Keep printing whilst all OK while (not Printer.Aborted) and Printer.Printing do begin
// Show a message saying we are starting a
page
ShowMessagePos('Starting to print page '+IntToStr(page),300,300);
// Set up a medium sized font
Printer.Canvas.Font.Size := 10;
// Allow Windows to keep processing
messages
Application.ProcessMessages;
// Write out the page number
Printer.Canvas.Font.Color := clBlue;
Printer.Canvas.TextOut(40,20, 'Page number = '+IntToStr(page));
// Underline this page number
Printer.Canvas.MoveTo(40,80);
Printer.Canvas.LineTo(Printer.PageWidth-20,80);
