概要

本分步指南介绍了如何打印 RichTextBox 控件的内容。RichTextBox 控件没有提供任何打印 RichTextBox 内容的方法。您可以扩展 RichTextBox 类以使用 EM_FORMATRANGE 消息将 RichTextBox 控件的内容发送到一个输出设备（如打印机）。

 

创建 RichTextBoxPrintCtrl 控件 下面的示例介绍了如何扩展 RichTextBox 类，以及如何使用 EM_FORMATRANGE 打印 RichTextBox 控件的内容。

在 Visual C# .NET 中，新建一个名为 RichTextBoxPrintCtrl 的类库项目。默认情况下创建 Class1.cs。

将 Class1.cs 的名称改为 RichTextBoxPrintCtrl.cs。

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”。

在“添加引用”对话框中，双击“System.Drawing.dll”和“System.Windows.Forms.dll”，，然后单击“确定”。

将 RichTextBoxPrintCtl.cs 中的现有代码替换为以下代码：

using System; using System.Windows.Forms; using System.Drawing; using System.Runtime.InteropServices; using System.Drawing.Printing; namespace RichTextBoxPrintCtrl { public class RichTextBoxPrintCtrl:RichTextBox { //Convert the unit used by the .NET framework (1/100 inch) //and the unit used by Win32 API calls (twips 1/1440 inch) private const double anInch = 14.4; [StructLayout(LayoutKind.Sequential)] private struct RECT { public int Left; public int Top; public int Right; public int Bottom; } [StructLayout(LayoutKind.Sequential)] private struct CHARRANGE { public int cpMin; //First character of range (0 for start of doc) public int cpMax; //Last character of range (-1 for end of doc) } [StructLayout(LayoutKind.Sequential)] private struct FORMATRANGE { public IntPtr hdc; //Actual DC to draw on public IntPtr hdcTarget; //Target DC for determining text formatting public RECT rc; //Region of the DC to draw to (in twips) public RECT rcPage; //Region of the whole DC (page size) (in twips) public CHARRANGE chrg; //Range of text to draw (see earlier declaration) } private const int WM_USER = 0x0400; private const int EM_FORMATRANGE = WM_USER + 57; [DllImport("USER32.dll")] private static extern IntPtr SendMessage (IntPtr hWnd , int msg , IntPtr wp, IntPtr lp); // Render the contents of the RichTextBox for printing // Return the last character printed + 1 (printing start from this point for next page) public int Print( int charFrom, int charTo,PrintPageEventArgs e) { //Calculate the area to render and print RECT rectToPrint; rectToPrint.Top = (int)(e.MarginBounds.Top * anInch); rectToPrint.Bottom = (int)(e.MarginBounds.Bottom * anInch); rectToPrint.Left = (int)(e.MarginBounds.Left * anInch); rectToPrint.Right = (int)(e.MarginBounds.Right * anInch); //Calculate the size of the page RECT rectPage; rectPage.Top = (int)(e.PageBounds.Top * anInch); rectPage.Bottom = (int)(e.PageBounds.Bottom * anInch); rectPage.Left = (int)(e.PageBounds.Left * anInch); rectPage.Right = (int)(e.PageBounds.Right * anInch); IntPtr hdc = e.Graphics.GetHdc(); FORMATRANGE fmtRange; fmtRange.chrg.cpMax = charTo; //Indicate character from to character to fmtRange.chrg.cpMin = charFrom; fmtRange.hdc = hdc; //Use the same DC for measuring and rendering fmtRange.hdcTarget = hdc; //Point at printer hDC fmtRange.rc = rectToPrint; //Indicate the area on page to print fmtRange.rcPage = rectPage; //Indicate size of page IntPtr res = IntPtr.Zero; IntPtr wparam = IntPtr.Zero; wparam = new IntPtr(1); //Get the pointer to the FORMATRANGE structure in memory IntPtr lparam= IntPtr.Zero; lparam = Marshal.AllocCoTaskMem(Marshal.SizeOf(fmtRange)); Marshal.StructureToPtr(fmtRange, lparam, false); //Send the rendered data for printing res = SendMessage(Handle, EM_FORMATRANGE, wparam, lparam); //Free the block of memory allocated Marshal.FreeCoTaskMem(lparam); //Release the device context handle obtained by a previous call e.Graphics.ReleaseHdc(hdc); //Return last + 1 character printer return res.ToInt32(); } } }

在“生成”菜单中，单击“生成解决方案”以创建 RichTextBoxPrintCtrl.dll。

 

测试控件

在 Visual C# .NET 中创建一个新的 Windows 应用程序项目。默认情况下将创建出 Form1.cs。

将一个按钮控件从工具箱拖入 Form1。将 Name 属性更改为 btnPageSetup，并将 Text 属性更改为页面设置。

将另一个按钮控件从工具箱拖入 Form1。将 Name 属性更改为 btnPrintPreview，并将 Text 属性更改为打印预览。

将另一个按钮控件从工具箱拖入 Form1。将 Name 属性更改为 btnPrint，并将 Text 属性更改为打印。

在工具箱中，双击“PrintDialog”、“PrintPreviewDialog”、“PrintDocument”和“PageSetupDialog”以将这些控件添加到 Form1 中。