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ASP.NET 客户端回调实现 (C#) 示例 (VS2005)MSDN 错误处理

2008-11-25 17:11 1016 查看

最近研究了一下ASP.NET 客户端回调，在MSDN上找到了这个示例：

<%@ 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 xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<script type="text/javascript">
function LookUpStock()
{
var lb = document.forms[0].ListBox1;
var product = lb.options[lb.selectedIndex].text
CallServer(product, "");
}

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 onclick="LookUpStock()">Look Up Stock</button>
<br />
<br />
Items in stock: <span ID="Results"></span>
<br />
</div>
</form>
</body>
</html>

// ClientCallback.aspx.cs code-behind page
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 void Page_Load(object sender, EventArgs e)
{
String cbReference =
Page.ClientScript.GetCallbackEventReference(this,
"arg", "ReceiveServerData", "context");
String callbackScript;
callbackScript = "function CallServer(arg, context)" +
"{ " + cbReference + "} ;";
Page.ClientScript.RegisterClientScriptBlock(this.GetType(),
"CallServer", callbackScript, true);

catalog = new System.Collections.Specialized.ListDictionary();
catalog.Add("monitor", 12);
catalog.Add("laptop", 10);
catalog.Add("keyboard", 23);
catalog.Add("mouse", 17);

ListBox1.DataSource = catalog;
ListBox1.DataTextField = "key";
ListBox1.DataBind();
}

public String RaiseCallbackEvent(String eventArgument)
{
String returnValue;
if (catalog[eventArgument] == null)
{
returnValue = "-1";
}
else
{
returnValue = catalog[eventArgument].ToString();
}
return returnValue;
}
}

但执行有错误，System.Web.UI.ICallbackEventHandler 此接口方法实现的不正确。下面咱们看一下此接口的声明：

using System;

namespace System.Web.UI
{
// 摘要:
//     用于指示控件可以作为服务器的回调事件的目标。
public interface ICallbackEventHandler
{
// 摘要:
//     返回以控件为目标的回调事件的结果。
//
// 返回结果:
//     回调的结果。
string GetCallbackResult();
//
// 摘要:
//     处理以控件为目标的回调事件。
//
// 参数:
//   eventArgument:
//     一个字符串，表示要传递到事件处理程序的事件参数。
void RaiseCallbackEvent(string eventArgument);
}
}

看明白了吧，MSDN示例 实现System.Web.UI.ICallbackEventHandler 这个接口有问题

我更改了一下 RaiseCallbackEvent(string eventArgument)此方法返回值应该是无类型的，还有必须实现此方法：string GetCallbackResult() 。更改后此示例就通过了，下面是修改后的源码：

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;
public string returnValue = string.Empty;
protected void Page_Load(object sender, EventArgs e)
{
String cbReference =
Page.ClientScript.GetCallbackEventReference(this,
"arg", "ReceiveServerData", "context");
String callbackScript;
callbackScript = "function CallServer(arg, context)" +
"{ " + cbReference + "} ;";
Page.ClientScript.RegisterClientScriptBlock(this.GetType(),
"CallServer", callbackScript, true);

catalog = new System.Collections.Specialized.ListDictionary();
catalog.Add("monitor", 12);
catalog.Add("laptop", 10);
catalog.Add("keyboard", 23);
catalog.Add("mouse", 17);

ListBox1.DataSource = catalog;
ListBox1.DataTextField = "key";
ListBox1.DataBind();
}

public void RaiseCallbackEvent(String eventArgument)
{
if (catalog[eventArgument] == null)
{
returnValue = "-1";
}
else
{
returnValue = catalog[eventArgument].ToString();
}
//return returnValue;
}

// Define method that returns callback result.
public string GetCallbackResult()
{
return returnValue;
}
}
不知大家看明白了没有

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