错误如下图：

当我们在写web程序的时候，有时候避免不了要再后台弹出一个提示框，在winform中我们可以用MssageBox() 类来实现，在web开发中，我们只能借助于javascript来实现了

.net中为我们提供了这样一个类ScriptManager来帮助我们解决这样的问题，而有些时候我们却在使用的时候容易出现这样一个错误，”当前上下文不存在 ScriptManager ” ，这就很郁闷了，差资料显示 ScriptManager 类存在于 System.Web.UI 命名空间中，这时我们在类的头部添加引用，using System.Web.UI;或者是继承 System.Web.UI.Page 这样还是不行，郁闷了，查资料，显示  System.Web.UI类存在于 程序集：  System.Web.Extensions（在 System.Web.Extensions.dll 中），这时，有人会在类头部这样写，Using System.Web.Extensions; 这样是不行的，我们必须在项目中，添加引用，

示例如下图：

第二步：

“

msdn论坛：http://msdn.microsoft.com/zh-cn/library/system.web.ui.scriptmanager%28v=vs.100%29.aspx点击打开链接

示例类如下：类PageUtil

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;namespace shouqiang_Wei{public class PageUtil:System.Web.UI.Page{#region 截取字符长度/// <summary>/// 截取字符长度/// </summary>/// <param name="inputString">字符</param>/// <param name="len">长度</param>/// <returns></returns>public static string CutString(string inputString, int len){if (string.IsNullOrEmpty(inputString))return "";inputString = DropHTML(inputString);ASCIIEncoding ascii = new ASCIIEncoding();int tempLen = 0;string tempString = "";byte[] s = ascii.GetBytes(inputString);for (int i = 0; i < s.Length; i++){if ((int)s[i] == 63){tempLen += 2;}else{tempLen += 1;}try{tempString += inputString.Substring(i, 1);}catch{break;}if (tempLen > len)break;}//如果截过则加上半个省略号 byte[] mybyte = System.Text.Encoding.Default.GetBytes(inputString);if (mybyte.Length > len)tempString += "…";return tempString;}#endregion#region 清除HTML标记public static string DropHTML(string Htmlstring){if (string.IsNullOrEmpty(Htmlstring)) return "";//删除脚本  Htmlstring = Regex.Replace(Htmlstring, @"<script[^>]*?>.*?</script>", "", RegexOptions.IgnoreCase);//删除HTML  Htmlstring = Regex.Replace(Htmlstring, @"<(.[^>]*)>", "", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"([\r\n])[\s]+", "", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"-->", "", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"<!--.*", "", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"&(quot|#34);", "\"", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"&(amp|#38);", "&", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"&(lt|#60);", "<", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"&(gt|#62);", ">", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"&(nbsp|#160);", " ", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"&(iexcl|#161);", "\xa1", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"&(cent|#162);", "\xa2", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"&(pound|#163);", "\xa3", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"&(copy|#169);", "\xa9", RegexOptions.IgnoreCase);Htmlstring = Regex.Replace(Htmlstring, @"&#(\d+);", "", RegexOptions.IgnoreCase);Htmlstring.Replace("<", "");Htmlstring.Replace(">", "");Htmlstring.Replace("\r\n", "");Htmlstring = HttpContext.Current.Server.HtmlEncode(Htmlstring).Trim();return Htmlstring;}#endregion/// <summary>/// 在web页面上显示一个对话框/// </summary>/// <param name="page"></param>/// <param name="msg"></param>public static void ShowMsgBox(System.Web.UI.Control page, string msg){string m = HttpUtility.HtmlEncode(msg);ExecJavaScript(page, "alert('" + m + "');");}public static void ShowCfmMsgBox(System.Web.UI.Control page, string msg){string m = HttpUtility.HtmlEncode(msg);ExecJavaScript(page, "confirm('" + m + "');");}/// <summary>/// 显示提示信息并转向新的页面/// </summary>/// <param name="page"></param>/// <param name="msg"></param>/// <param name="newurl"></param>public static void ShowMsgBoxAndRedirect(System.Web.UI.Control page, string msg, string newurl){string m = HttpUtility.HtmlEncode(msg);ExecJavaScript(page, "alert('" + m + "'); window.location='" + newurl + "';");}/// <summary>/// Add by shouqiang Wei 改成 confirm 这样的话就可以返回了...> 不知道能不能行？/// </summary>/// <param name="page"></param>/// <param name="msg"></param>/// <param name="newurl"></param>public static void ShowCfmMsgBoxAndRedirect(System.Web.UI.Control page, string msg, string newurl){string m = HttpUtility.HtmlEncode(msg);ExecJavaScript(page, "if(confirm('" + m + "')) window.location='" + newurl + "' ;");}/// <summary>/// 子框架中转向/// </summary>/// <param name="page"></param>/// <param name="newurl"></param>public static void ParentPageRedirect(System.Web.UI.Control page, string newurl){ExecJavaScript(page, " self.parent.window.location='" + newurl + "';");}/// <summary>/// 在web页面上添加一段javascript/// </summary>/// <param name="page"></param>/// <param name="script"></param>public static void ExecJavaScript(System.Web.UI.Control page, string script){ScriptManager.RegisterStartupScript(page, page.GetType(), "a", script, true);}/// <summary>/// MD5摘要/// </summary>/// <param name="cleanString"></param>/// <returns></returns>public static string Md5Encrypt(string cleanString){Byte[] clearBytes = new UnicodeEncoding().GetBytes(cleanString);Byte[] hashedBytes = ((HashAlgorithm)CryptoConfig.CreateFromName("MD5")).ComputeHash(clearBytes);return BitConverter.ToString(hashedBytes);}/// <summary>/// SQL防注入攻击，数据过滤/// </summary>/// <param name="value">要过滤的数据</param>/// <returns>过滤后的数据</returns>public static string SQLFilter(string value){if (String.IsNullOrEmpty(value)) return "";value = value.Trim();value = HttpUtility.HtmlEncode(value);value = value.Replace(" and ", "***");value = value.Replace(" or ", "***");value = value.Replace(" truncate ", "***");value = value.Replace(" from ", "***");value = value.Replace(" select ", "***");value = value.Replace(" insert ", "***");value = value.Replace(" update ", "***");value = value.Replace(" delete ", "***");value = value.Replace(" drop ", "***");value = value.Replace(" count ", "***");value = value.Replace(" exec ", "***");return value;}public static string GetSex(object obj){if (obj == null){return "未知";}try{bool sex = bool.Parse(obj.ToString());if (sex){return "男";}elsereturn "女";}catch (Exception ex){return "未知";}}public static string GetClosedStatus(object obj){if (obj == null){return "未知";}else{try{int n = int.Parse(obj.ToString());if (n == 1){return "关闭";}else if (n == 0)return "开放";elsereturn "未知";}catch (Exception ex){return "未知";}}}public static string SubString(object obj, int length){if (obj == null)return "";string str = obj.ToString();if (str.Length > length)return str.Substring(0, length);return str;}}
}