Silverlight 2.0 正式版发布之后，在 HttpWebrequest 方面也发生了一些变化，以前的代码正式版里面可能就无法运行了，具体的变化主要有：
1，在调用 HttpWebRequest.BeginGetResponse() 之前，Request 流必须关闭；
2，HttpWebRequest.EndGetResponse() 抛出的异常，正式版之前，HttpWebRequest.BeingGetResponse() 中跨域、跨协议访问抛出安全性异常，其他的请求都返回404错误，现在，HttpRequest.EndGetResponse()的错误将作为异常抛出，涉及安全问题的错误抛出 SecurityException，非成功的请求会抛出 WebException 异常，WebException.Response 被设置成 HttpStatusCode.NotFound。
由于 HttpWebrequest 发送的是异步请求，如果要与界面交互，还涉及到线程同步的问题，如果不进行线程同步，会报告“跨线程访问无效”的错误。下面就以实际的例子来向一个 Java Servlet 地址提交数据，将提交的数据返回到当前界面中。当然，提交到 aspx 页面上也没有问题的，只需要在 Page_Load 事件处理方法里加入下面的代码即可：
<![CDATA[protected void Page_Load(object sender, EventArgs e)
{
if (Request.RequestType.Equals("POST"))
{
Response.ClearContent();
Response.ClearHeaders();
Response.Write("您提交的数据是：" + Request.Params.Get("data"));
Response.End();
return;
}
}
]]>
如果提交到 Java Servlet，则测试代码可以写：
<![CDATA[public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.getWriter().print("您提交的数据是：" + request.getParameter("data"));
}
]]>
要在本机进行跨域测试，需要在hosts文件进行设置，如：
127.0.0.1 www.mengxianhui.com 127.0.0.1 www.xianhuimeng.com
这样，就可以在你自己的机器上进行跨域测试了，不过，需要记住，默认情况下，Silverlight 是不允许跨域访问的，因此，需要在接收数据的网站根目录下（记住是网站根目录，不是应用程序的根目录）放置一个策略文件，clientaccesspolicy.xml 或者 crossdomain.xml ：
clientaccesspolicy.xml 内容设置如下：
<![CDATA[<?xml version="1.0" encoding="utf-8" ?>
<access-policy>
<cross-domain-access>
<policy>
<allow-from http-request-headers="*">
<domain uri="*" />
</allow-from>
<grant-to>
<resource path="/" include-subpaths="true" />
</grant-to>
</policy>
</cross-domain-access>
</access-policy>
]]>
crossdomain.xml 内容设置如下：
<![CDATA[<?xml version="1.0" ?>
<!doctype cross-domain-policy SYSTEM "http://www.macromedia.com/xml/dtds/cross-domain-policy.dtd">
<cross-domain-policy>
<allow-http-request-headers-from domain="*" headers="*" />
</cross-domain-policy>
]]>
本例子中使用的 Page.xaml 如下：
<![CDATA[<usercontrol xmlns:basics="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls" x:class="SilverlightApplication3.Page" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" width="400" height="300">
<grid x:name="LayoutRoot" background="White">
<canvas width="400" height="300" Canvas. left="2">
<textbox x:name="data" Canvas. left="2" Canvas. top="2" height="30" width="180" text="【孟子E章】测试数据" fontsize="16"></textbox>
<button content="发送POST数据" width="100" height="30" click="PostData" Canvas. top="2" Canvas. left="200"></button>
<textblock x:name="result" Canvas. top="40" fontsize="16"></textblock>
</canvas>
</grid>
</usercontrol>
]]>
Page.xaml.cs 完整内容
<![CDATA[using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Text;
using System.IO;
using System.Diagnostics;
using System.Threading;
namespace SilverlightApplication3
{
public partial class Page : UserControl
{
public Page()
{
InitializeComponent();
//设置当前界面线程
syncContext = SynchronizationContext.Current;
}
private SynchronizationContext syncContext;
private String postData = String.Empty;
private void PostData(object sender, RoutedEventArgs e)
{
//请注意：Silverlight 里的 HttpWebRequest, Encoding 类的属性和方法与常规的 .NET Framework 里面还是不同的。
result.Text = "开始提交数据……";
postData = "data=" + data.Text; //要提交的内容
Uri url = new Uri("http://www.mengxianhui.com/admin?tmp=" + DateTime.Now.Ticks.ToString(), UriKind.Absolute);
System.Net.HttpWebRequest request = (System.Net.HttpWebRequest)WebRequest.Create(url);
request.Method = "POST"; // Silverlight 只支持 GET 和 POST 方法
request.AllowReadStreamBuffering = true;
request.ContentType = "application/x-www-form-urlencoded";
request.BeginGetRequestStream(new AsyncCallback(RequestReady), request);
}
private void RequestReady(IAsyncResult asyncResult)
{
HttpWebRequest request = asyncResult.AsyncState as HttpWebRequest;
StreamWriter postStream = new StreamWriter(request.EndGetRequestStream(asyncResult));
//byte[] byteArray = Encoding.UTF8.GetBytes(postData);
//Encoding.GetEncoding()方法只支持四种编码。utf-8 , utf-16 , utf-16BE , utf-16LE
postStream.Write(postData); //处理中文的问题。不要使用 Stream 的 Write 方法。
postStream.Close();
postStream.Dispose();
request.BeginGetResponse(new AsyncCallback(ResponseReady), request);
}
void ResponseReady(IAsyncResult asyncResult)
{
HttpWebRequest request = asyncResult.AsyncState as HttpWebRequest;
WebResponse response = request.EndGetResponse(asyncResult) as WebResponse;
//同步线程上下文
if (syncContext == null) syncContext = new SynchronizationContext();
syncContext.Post(ExtractResponse, response);
}
private void ExtractResponse(object state)
{
WebResponse response = state as WebResponse;
Stream responseStream = response.GetResponseStream();
StreamReader streamRead = new StreamReader(responseStream);
//显示返回的数据
result.Text = new StreamReader(responseStream).ReadToEnd();
response.Close();
responseStream.Close();
responseStream.Dispose();
streamRead.Close();
streamRead.Dispose();
}
}
}
]]>
