Know Dot Net Article

Printing a Windows Form

by Les Smith and Brian Davis

VB6 had a PrintForm method, but .NET does not appear to provide the same functionality.  How can I print a Windows Form?

You can still print a form at run time from VB.NET or C#.  It's just not an included method in a form.  It takes just a little work and the use of an API.  This article will give you the code for printing a form at run-time.

This code is a modification of the code found on the Microsoft Site.  We have attempted to make some enhancements to the basic code provided by Microsoft.  We have extended the code to cause it to print the Title Bar and form borders, which the original code does not do.  This code has been tested on Windows 2000, but not on Windows XP.  Windows XP rounds the borders of the form Title Bar, so you can expect a minor change in the appearance of the printed form.

First, we created a simple form with a few controls, that do nothing, so that the form would have something on it.  We added a Print Form command button and called it btnPrintForm.

Place the following code in the declaractions section of your form.  This code sets up a PrintDocument component and declares the prototype for the BitBlt API call.  The BitBlt function performs a bit-block transfer of the color data corresponding to a rectangle of pixels from the specified source device context into a destination device context. This API is used to capture the image of the form.

   ' create a printing component
   Private WithEvents pd As Printing.PrintDocument
   ' storage for form image
   Dim formImage As Bitmap
   ' create API prototype
   Private Declare Function BitBlt Lib "gdi32.dll" Alias _
      "BitBlt" (ByVal hdcDest As IntPtr, _
      ByVal nXDest As Integer, ByVal nYDest As _
      Integer, ByVal nWidth As Integer, _
      ByVal nHeight As Integer, ByVal _
      hdcSrc As IntPtr, ByVal nXSrc As Integer, _
      ByVal nYSrc As Integer, _
      ByVal dwRop As System.Int32) As Long

Next, place the following event handlers in the code window of the form.  The print command button is expected to have a Name of btnPrintForm.

   ' Callback from PrintDocument component to
   ' do the actual printing
   Private Sub pd_PrintPage(ByVal sender As Object, _
      ByVal e As System.Drawing.Printing.PrintPageEventArgs) _
      Handles pd.PrintPage
      e.Graphics.DrawImage(formImage, 100, 100)
   End Sub

   Private Sub Form1_Load(ByVal sender As Object, _
     ByVal e As System.EventArgs) Handles MyBase.Load
      ' create an instance of the PrintDocument component
      pd = New Printing.PrintDocument
      Me.StartPosition = FormStartPosition.CenterScreen
   End Sub

   Private Sub btnPrintForm_Click(ByVal sender As _
      System.Object, ByVal e As System.EventArgs) _
      Handles btnPrintForm.Click
      ' initiate the printdocument component
      GetFormImage()
      pd.Print()
   End Sub

In the Form_Load event, we have created an instance of the PrintDocument object.  In the btnPrintForm_Click event, we call a method, shown below, to capture the image of the form and create a Bitmap of it.  Then we call the Print method of the PrintDocument object to initiate the printing of the form.  That method will call the pd_PrintPage event handler to request the data to be printed.  In this case the data to be printed is a Bitmap, created by the GetFormImage method.

The following method, GetFormImage, captures the screen image of the form.

   Private Sub GetFormImage()
      Dim g As Graphics = Me.CreateGraphics()
      Dim s As Size = Me.Size
      formImage = New Bitmap(s.Width, s.Height, g)
      Dim mg As Graphics = Graphics.FromImage(formImage)
      Dim dc1 As IntPtr = g.GetHdc
      Dim dc2 As IntPtr = mg.GetHdc
      ' added code to compute and capture the form
      ' title bar and borders
      Dim widthDiff As Integer = _
         (Me.Width - Me.ClientRectangle.Width)
      Dim heightDiff As Integer = _
         (Me.Height - Me.ClientRectangle.Height)
      Dim borderSize As Integer = widthDiff \ 2
      Dim heightTitleBar As Integer = heightDiff - borderSize
      BitBlt(dc2, 0, 0, _
         Me.ClientRectangle.Width + widthDiff, _
         Me.ClientRectangle.Height + heightDiff, dc1, _
         0 - borderSize, 0 - heightTitleBar, 13369376)

      g.ReleaseHdc(dc1)
      mg.ReleaseHdc(dc2)
   End Sub

When we completed our form, ran the application, and clicked the Print Form button, it looked like the form shown in Figure 1.  Regardless of what your form looks like, if you place a Print Button or a Menu Option on it, and call the Click event handler shown above, your form should print properly.

Figure 1 - Demo Form.