Printing a Memo

Problem/Question/Abstract:

I have a simple editor unit with a TMemo component whose text I want to send to the printer. How can I do this?

Answer:

This is actually much easier that most people think, though you can get pretty fancy. With the procedure that I'll show you below, I will take advantage of the TMemo's Lines property, which is of type TStrings. The procedure will parse each line in the memo, and use Canvas.TextOut to print to the printer. After you see this code, you'll see how simple it is. Let's take a look at the code:

procedure PrintTStrings(Lst: TStrings);
var
  I, Line: Integer;
begin
  I := 0;
  Line := 0;
  Printer.BeginDoc;
  for I := 0 to Lst.Count - 1 do
  begin
    Printer.Canvas.TextOut(0, Line, Lst[I]);

    {Font.Height is calculated as -Font.Size * 72 / Font.PixelsPerInch which returns
     a negative number. So Abs() is applied to the Height to make it a non-negative
     value}
    Line := Line + Abs(Printer.Canvas.Font.Height);
    if (Line >= Printer.PageHeight) then
      Printer.NewPage;
  end;
  Printer.EndDoc;
end;

Basically, all we're doing is sequentially moving from the beginning of the TStrings object to the end with the for loop. At each line, we print the text using Canvas.TextOut then perform a line feed and repeat the process. If our line number is greater than the height of the page, we go to a new page. Notice that I extensively commented before the line feed. That's because feeding a line was the only tricky part of the code. When I first wrote this, I just added the Font height to the line, and thus the code would generate a smaller and smaller negative number. The net result was that I'd only print one line of the memo. Actually TextOut would output to the printer, but it essentially printed from the first line up, not down. So, after carefully reading the help file, I found that Height is the result of the calculation of a negative font size, so I used the Abs() function to make it a non-negative number.

For more complex operations, I suggest you look at the help file under Printer or TPrinter, and also study the TextOut procedure. Now, what is Printer? Well, when you make a call to Printer, it creates a global instance of TPrinter, which is Delphi's interface into the Windows print functions. With TPrinter, you can define everything which describes the page(s) to print: Page Orientation, Font (through the Canvas property), the Printer to print to, the Width and Height of the page, and many more things.