概要
本文逐步说明如何打印 RichTextBox 控件的内容。RichTextBox 控件不提供打印其内容的方法。但是，您可以扩展 RichTextBox 类以使用 EM_FORMATRANGE 消息。然后，您可以将 RichTextBox 的内容发送到某个输出设备，例如打印机。


创建 RichTextBoxPrintCtrl 控件
要扩展 RichTextBox 类并使用 EM_FORMATRANGE 来打印 RichTextBox 控件的内容，请按照下列步骤操作： 1. 使用 Microsoft Visual Basic .NET 新建一个名为 RichTextBoxPrintCtrl 的类库项目。

默认情况下，将创建 Class1.vb。
2. 将 Class1.vb 文件的名称更改为 RichTextBoxPrintCtrl.vb。
3. 在解决方案资源管理器中，右键单击“引用”，然后单击“添加引用”。
4. 在添加引用对话框中，双击“System.Drawing.dll”，然后双击“System.Windows.Forms.dll”。
5. 要添加引用，请单击“确定”。
6. 删除“RichTextBoxPrintCtrl.vb”中的现有节点。
7. 将以下代码复制到“RichTextBoxPrintCtrl.vb”中：
Option Explicit On

Imports System
Imports System.Windows.Forms
Imports System.Drawing
Imports System.Runtime.InteropServices
Imports System.Drawing.Printing

Namespace RichTextBoxPrintCtrl
Public Class RichTextBoxPrintCtrl
Inherits RichTextBox
' Convert the unit that is used by the .NET framework (1/100 inch)
' and the unit that is used by Win32 API calls (twips 1/1440 inch)
Private Const AnInch As Double = 14.4

<StructLayout(LayoutKind.Sequential)> _
Private Structure RECT
Public Left As Integer
Public Top As Integer
Public Right As Integer
Public Bottom As Integer
End Structure

<StructLayout(LayoutKind.Sequential)> _
Private Structure CHARRANGE
Public cpMin As Integer ' First character of range (0 for start of doc)
Public cpMax As Integer ' Last character of range (-1 for end of doc)
End Structure

<StructLayout(LayoutKind.Sequential)> _
Private Structure FORMATRANGE
Public hdc As IntPtr ' Actual DC to draw on
Public hdcTarget As IntPtr ' Target DC for determining text formatting
Public rc As Rect ' Region of the DC to draw to (in twips)
Public rcPage As Rect ' Region of the whole DC (page size) (in twips)
Public chrg As CHARRANGE ' Range of text to draw (see above declaration)
End Structure

Private Const WM_USER As Integer = &H400
Private Const EM_FORMATRANGE As Integer = WM_USER + 57

Private Declare Function SendMessage Lib "USER32" Alias "SendMessageA" (ByVal hWnd As IntPtr, ByVal msg As Integer, ByVal wp As IntPtr, ByVal lp As IntPtr) As IntPtr

' Render the contents of the RichTextBox for printing
' Return the last character printed + 1 (printing start from this point for next page)
Public Function Print(ByVal charFrom As Integer, ByVal charTo As Integer, ByVal e As PrintPageEventArgs) As Integer

' Mark starting and ending character
Dim cRange As CHARRANGE
cRange.cpMin = charFrom
cRange.cpMax = charTo

' Calculate the area to render and print
Dim rectToPrint As RECT
rectToPrint.Top = e.MarginBounds.Top * AnInch
rectToPrint.Bottom = e.MarginBounds.Bottom * AnInch
rectToPrint.Left = e.MarginBounds.Left * AnInch
rectToPrint.Right = e.MarginBounds.Right * AnInch

' Calculate the size of the page
Dim rectPage As RECT
rectPage.Top = e.PageBounds.Top * AnInch
rectPage.Bottom = e.PageBounds.Bottom * AnInch
rectPage.Left = e.PageBounds.Left * AnInch
rectPage.Right = e.PageBounds.Right * AnInch

Dim hdc As IntPtr = e.Graphics.GetHdc()

Dim fmtRange As FORMATRANGE
fmtRange.chrg = cRange ' Indicate character from to character to
fmtRange.hdc = hdc ' Use the same DC for measuring and