asp.net客户端回调

在ASP.NET中要实现页面的部分回发，除了使用AJAX外还可以使用客户端回调。

使用场景举例：一个很大的TreeView，初始化时只加载根节点，点击节点时加载子结点。

以下是简单的示例代码：（要注意脚本安全验证）

 
   

  
    
  
    
  
    <%
  
    
  
    @ Page Language="C#" AutoEventWireup="true" 
   CodeFile="ClientCallback.aspx.cs" Inherits="ClientCallback" 
  
    %>
  
    
 
 
  
    <!
  
    DOCTYPE html PUBLIC "-//W3C//DTD XHTML 
   1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"
  
    >
  
    
 
 
  
    <
  
    html  
  
    >
  
    
 
  
    <
  
    head 
  
    id
  
    ="Head1"
  
     runat
  
    ="server"
  
    >
  
    
     
  
    <
  
    title
  
    >
  
    ASP.NET Example
  
    </
  
    title
  
    >
  
    
 
  
    <
  
    script 
  
    type
  
    ="text/javascript"
  
    >
  
    
  
        
     function ReceiveServerData(rValue)
     {
         Results.innerText = rValue;
     }
   
  
    </
  
    script
  
    >
  
    
 
  
    </
  
    head
  
    >
  
    
 
  
    <
  
    body
  
    >
  
    
   
  
    <
  
    form 
  
    id
  
    ="form1"
  
     runat
  
    ="server"
  
    >
  
    
     
  
    <
  
    div
  
    >
  
    
       
  
    <
  
    asp:ListBox 
  
    id
  
    ="ListBox1"
  
     runat
  
    ="server"
  
    ></
  
    asp:ListBox
  
    >
  
    
       
  
    <
  
    br 
  
    />
  
    
       
  
    <
  
    br 
  
    />
  
    
       
  
    <
  
    button 
  
    id
  
    ="LookUpStockButton"
  
     onclick
  
    ="LookUpStock()"
  
    >
  
    Look Up Stock
  
    </
  
    button
  
    >
  
    
       
  
    <
  
    asp:LoginView 
  
    id
  
    ="LoginView1"
  
     runat
  
    ="server"
  
    >
  
    
       
  
    <
  
    LoggedInTemplate
  
    >
  
    
          
  
    <
  
    button 
  
    id
  
    ="LookUpSaleButton"
  
     onclick
  
    ="LookUpSale()"
  
    >
  
    Look Up Back Order
  
    </
  
    button
  
    >
  
    
       
  
    </
  
    LoggedInTemplate
  
    >
  
    
       
  
    </
  
    asp:LoginView
  
    >
  
    
       
  
    <
  
    br 
  
    />
  
    
       Item status: 
  
    <
  
    span 
  
    id
  
    ="Results"
  
    ></
  
    span
  
    >
  
    
     
  
    </
  
    div
  
    >
  
    
   
  
    </
  
    form
  
    >
  
    
 
  
    </
  
    body
  
    >
  
    
 
  
    </
  
    html
  
    >
 
   

CodeBehind：

 
   

  
    
  
    using
  
     System;
 
  
    using
  
     System.Data;
 
  
    using
  
     System.Configuration;
 
  
    using
  
     System.Collections;
 
  
    using
  
     System.Web;
 
  
    using
  
     System.Web.Security;
 
  
    using
  
     System.Web.UI;
 
  
    using
  
     System.Web.UI.WebControls;
 
  
    using
  
     System.Web.UI.WebControls.WebParts;
 
  
    using
  
     System.Web.UI.HtmlControls;
 
 
  
    public
  
     
  
    partial
  
     
  
    class
  
     ClientCallback : System.Web.UI.Page,
      System.Web.UI.ICallbackEventHandler
 
  
    
  
    {
     protected System.Collections.Specialized.ListDictionary catalog;
     protected System.Collections.Specialized.ListDictionary saleitem;
     protected String returnValue;
     protected String validationLookUpStock = "LookUpStock";
     protected String validationLookUpSale = "LookUpSale";
     protected void Page_Load(object sender, EventArgs e)
     {
         Page.ClientScript.RegisterClientScriptBlock(this.GetType(),
             validationLookUpStock, "function LookUpStock() {  " +
             "var lb = document.forms[0].ListBox1; " +
             "var product = lb.options[lb.selectedIndex].text;  " +
             @"CallServer(product, ""LookUpStock"");}  ", true);
         if (User.Identity.IsAuthenticated)
         {
             Page.ClientScript.RegisterClientScriptBlock(this.GetType(),
             validationLookUpSale, "function LookUpSale() {  " +
             "var lb = document.forms[0].ListBox1; " +
             "var product = lb.options[lb.selectedIndex].text;  " +
             @"CallServer(product, ""LookUpSale"");} ", true);
         }
 
         String cbReference = "var param = arg + '|' + context;" + 
             Page.ClientScript.GetCallbackEventReference(this,
             "param", "ReceiveServerData", "context");
         String callbackScript;
         callbackScript = "function CallServer(arg, context)" +
             "{ " + cbReference + "} ;";
         Page.ClientScript.RegisterClientScriptBlock(this.GetType(),
             "CallServer", callbackScript, true);
 
         catalog = new System.Collections.Specialized.ListDictionary();
         saleitem = new System.Collections.Specialized.ListDictionary();
         catalog.Add("monitor", 12);
         catalog.Add("laptop", 10);
         catalog.Add("keyboard", 23);
         catalog.Add("mouse", 17);
         saleitem.Add("monitor", 1);
         saleitem.Add("laptop", 0);
         saleitem.Add("keyboard", 0);
         saleitem.Add("mouse", 1);
 
         ListBox1.DataSource = catalog;
         ListBox1.DataTextField = "key";
         ListBox1.DataBind();
     }
     public void RaiseCallbackEvent(String eventArgument)
     {
         string[] argParts = eventArgument.Split('|');
         if ((argParts == null) || (argParts.Length != 2))
         {
             returnValue = "A problem occurred trying to retrieve stock count.";
             return;
         }
         string product = argParts[0];
         string validationaction = argParts[1];
         switch (validationaction)
         {
             case "LookUpStock":
                 try
                 {
                     Page.ClientScript.ValidateEvent("LookUpStockButton", validationaction);
                     if (catalog[product] == null)
                     {
                         returnValue = "Item not found.";
                     }
                     else
                     {
                         returnValue = catalog[product].ToString() + " in stock.";
                     }
                 }
                 catch
                 {
                     returnValue = "Can not retrieve stock count.";
                 } 
                 break;
             case "LookUpSale":
                 try
                 {
                     Page.ClientScript.ValidateEvent("LookUpSaleButton", validationaction);
                     if (saleitem[product] == null)
                     {
                         returnValue = "Item not found.";
                     }
                     else
                     {
                         if (Convert.ToBoolean(saleitem[product]))
                             returnValue = "Item is on sale.";
                         else
                             returnValue = "Item is not on sale.";
                     }
                 }
                 catch
                 {
                     returnValue = "Can not retrieve sale status.";
                 }
                 break;
         }
 
     }
     public String GetCallbackResult()
     {
         return returnValue;
     }
     protected override void Render(HtmlTextWriter writer)
     {
         Page.ClientScript.RegisterForEventValidation("LookUpStockButton",
             validationLookUpStock);
         if (User.Identity.IsAuthenticated)
         {
             Page.ClientScript.RegisterForEventValidation("LookUpSaleButton",
                 validationLookUpSale);
         }
         base.Render(writer);
     }
 }