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。
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);
}
}
