你现在的代码基于打印到一个矩形： e.MarginBounds

对于测试，我使用了下面的代码：

  Private pageNum As Integer 

 Private Sub Button1_Click（ByVal sender As Object，ByVal e As EventArgs）_ 
 Handles Button1.Click 
 Dim sb As New StringBuilder 
 For i As Integer = 1 To 100 
 sb.AppendLine（i.ToString&）这是一行。）
下一个
 stringToPrint = sb .ToString 
 $ b pageNum = 0 
使用pvw作为新的PrintPreviewDialog（）
 pvw.Document = printDocument1 
 pvw.ShowDialog（）
结束使用
 End Sub 
 

然后我改变你的例程在第一页上使用一个更小的矩形： p>

  Private Sub printDocument1_PrintPage（ByVal sender As Object，_ 
 ByVal e As PrintPageEventArgs）_ 
 Handles printDocument1.PrintPage 
 Dim charactersOnPage As Integer = 0 
 Dim linesPerPage As Integer = 0 

 pageNum + = 1 

 Dim printSize As Size = e.MarginBounds.Size 
如果pageNum = 1然后
 printSize =新大小（printSize.Width，printSize.Height / 2）
 End If 
 e.Graphics.MeasureString（stringToPrint，Me.Font，printSize，_ 
 StringFormat.GenericTypographic，charactersOnPage，linesPerPage）

'在页面边界内绘制字符串
 e.Graphics.DrawString（stringToPrint，Me.Font，Brushes.Black，_ 
 New Rectangle（e.MarginBounds.Location，printSize），_ 
 StringFormat.GenericTypographic）

删除已经打印的字符串部分。 
 stringToPrint = stringToPrint.Substring（charactersOnPage）

检查是否打印更多的页面。 
 e.HasMorePages = stringToPrint.Length> 0 
 End Sub 
 

如果您需要控制基于字符的打印，去掉打印文本块的代码，并逐行打印所有内容。

So I am trying to force a page break while printing directly from my VB.NET program. I am basically using this code from MSDN to print my document:

Private Sub printDocument1_PrintPage(ByVal sender As Object, _
    ByVal e As PrintPageEventArgs)

    Dim charactersOnPage As Integer = 0
    Dim linesPerPage As Integer = 0

    ' Sets the value of charactersOnPage to the number of characters 
    ' of stringToPrint that will fit within the bounds of the page.
    e.Graphics.MeasureString(stringToPrint, Me.Font, e.MarginBounds.Size, _
        StringFormat.GenericTypographic, charactersOnPage, linesPerPage)

    ' Draws the string within the bounds of the page
    e.Graphics.DrawString(stringToPrint, Me.Font, Brushes.Black, _
    e.MarginBounds, StringFormat.GenericTypographic)

   ' Remove the portion of the string that has been printed.
    stringToPrint = stringToPrint.Substring(charactersOnPage)

    ' Check to see if more pages are to be printed.
    e.HasMorePages = stringToPrint.Length > 0

End Sub

This allows it to print fine, but I would like to put page breaks in specific spots. I've tried e.HasMorePages = true, but I don't understand how this allows me to break at specific locations. Say my stringToPrint is 5000 characters long, and I want to start a new page after 1000 characters, and then again after the next 2500 characters. How would I do this?

Also, changing linesOnPage and charactersOnPage to other values doesn't seem to change anything at all.

EDIT: I guess a little more info about what my program does will help. Basically what it's doing is the program will create about 4 full pages of data, and prints it to a .txt file. Now, I want to print the entire .txt file. The only way that I know how to do this is by printing a string, so I have it read the entire .txt file line by line and stores it all as one string (namely stringToPrint). Now, using the code above, I print stringToPrint.

Your current code is based on printing to a rectangle: e.MarginBounds

For testing, I used this code:

Private pageNum As Integer

Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) _
                          Handles Button1.Click
  Dim sb As New StringBuilder
  For i As Integer = 1 To 100
    sb.AppendLine(i.ToString & ") This is a line.")
  Next
  stringToPrint = sb.ToString

  pageNum = 0
  Using pvw As New PrintPreviewDialog()
    pvw.Document = printDocument1
    pvw.ShowDialog()
  End Using
End Sub

Then I changed your routine to use a smaller rectangle on the first page:

Private Sub printDocument1_PrintPage(ByVal sender As Object, _
                                     ByVal e As PrintPageEventArgs) _
                                     Handles printDocument1.PrintPage
  Dim charactersOnPage As Integer = 0
  Dim linesPerPage As Integer = 0

  pageNum += 1

  Dim printSize As Size = e.MarginBounds.Size
  If pageNum = 1 Then
    printSize = New Size(printSize.Width, printSize.Height / 2)
  End If
  e.Graphics.MeasureString(stringToPrint, Me.Font, printSize, _
      StringFormat.GenericTypographic, charactersOnPage, linesPerPage)

  ' Draws the string within the bounds of the page
  e.Graphics.DrawString(stringToPrint, Me.Font, Brushes.Black, _
    New Rectangle(e.MarginBounds.Location, printSize), _
    StringFormat.GenericTypographic)

  ' Remove the portion of the string that has been printed.
  stringToPrint = stringToPrint.Substring(charactersOnPage)

  ' Check to see if more pages are to be printed.
  e.HasMorePages = stringToPrint.Length > 0
End Sub

If you need to control the printing based on characters, you would have to ditch the code that prints the block of text and print everything on a line by line basis.