Printing in VB.NET

Components, components, components.  Using components is the difference between writing an application in one week vs. an application in a few hours.  Printing is all carried out through components included in the toolbox.   The main component that talks to the printer is the PrintDocument component.  To use this component, just call the Print function and intercept the PrintPage event.  Below are the routines that do this:

Protected Sub PrintFile_Click(sender As Object, e As System.EventArgs)printDialog1.Document = ThePrintDocument
Dim strText As String = Me.richTextBox1.Text
myReader = New StringReader(strText)
If printDialog1.ShowDialog() = DialogResult.OK Then
Me.ThePrintDocument.Print()
End If
End Sub 'PrintFile_Click
Protected Sub ThePrintDocument_PrintPage(sender As Object, ev As System.Drawing.Printing.PrintPageEventArgs)
Dim linesPerPage As Single = 0
Dim yPosition As Single = 0
Dim count As Integer = 0
Dim leftMargin As Single = ev.MarginBounds.Left
Dim topMargin As Single = ev.MarginBounds.Top
Dim line As String = Nothing
Dim printFont As Font = Me.richTextBox1.Font
Dim myBrush As New SolidBrush(Color.Black)
' Work out the number of lines per page, using the MarginBounds.
linesPerPage = ev.MarginBounds.Height / printFont.GetHeight(ev.Graphics)
' Iterate over the string using the StringReader, printing each line.
While count < linesPerPage And Not ((line <<= myReader.ReadLine()) Is Nothing) 'ToDo: Unsupported feature: assignment within expression. "=" changed to "<="
' calculate the next line position based on
' the height of the font according to the printing device yPosition = topMargin + (count * printFont.GetHeight(ev.Graphics));// draw the next line in the rich edit control
ev.Graphics.DrawString(line, printFont, myBrush, leftMargin, yPosition, New StringFormat())
count += 1
End While ' If there are more lines, print another page. if (line != null)ev.HasMorePages = True
ev.HasMorePages = False
myBrush.Dispose()
End Sub 'ThePrintDocument_PrintPage

PrintFile_Click is called from the Print Menu.This routine first assigns the PrintDialog component to the document being printed.  The dialog is shown using ShowDialog so the user can set their print settings and to decide whether to print or not.  After ThePrintDocument.Print is called, the printing process begins.  The PrintPage event is automatically called by the system to print the desired page information.  The PrintPageEventArgs ev contains the Device Contexts ev.Graphics to use for drawing to the Printer.  In this example we read each line of text from the rich text edit control using a StringReader.  The StringReader class gives us the ability to treat a string like a stream and take advantage of the ReadLine function of the StringReader for reading each line out of the text edit control.  We can calculate the position of the lines based on margins and the height of the font.  It's interesting to note, that in order to predict the font height for the printer, we pass it the Device context of the printer in the GetHeight function (printFont.GetHeight(ev.Graphics())).  This is because the font height on the screen pixels is different than the font height in printer pixels.  The PrintPageEventArg attribute HasMorePages is continually set so that the PrintPage Event is triggered if there are more lines in the textbox than the current page can hold.

Print Preview

PrintPreview behaves a heck of a lot like Print as seen below:

Protected Sub PreviewFile_Click(sender As Object, e As System.EventArgs)
Try
Dim strText As String = Me.richTextBox1.Text ' read string from editor window
myReader = New StringReader(strText)
Dim printPreviewDialog1 As New PrintPreviewDialog() ' instantiate new print preview dialog
printPreviewDialog1.Document = Me.ThePrintDocument
printPreviewDialog1.BorderStyle = FormBorderStyle.Fixed3D
printPreviewDialog1.ShowDialog() ' Show the print preview dialog, uses print page event to draw preview screen
Catch exp As Exception
System.Console.WriteLine(exp.Message.ToString())
End Try
End Sub 'PreviewFile_Click

The PrintPreview component also triggers the PrintPage event, but instead of outputting to the printer it outputs to the Print Preview Screen. 

Other Editor Functions

The Open and Save menu items use streams to read and write the files.  The persistence of files is discussed in other articles on this site.