使用Silverlight获取页面的html内容

Question

我试图使用Silverlight获取页面的html内容。 Web响应和请求类不能在silverlight中工作。

我做了一些谷歌搜索，我发现了一些东西。这是我的尝试：

public partial class MainPage : UserControl 
{ 
    string result; 
    WebClient client; 

    public MainPage() 
    { 
    InitializeComponent(); 
    this.result = string.Empty; 
    this.client = new WebClient(); 
    this.client.DownloadStringCompleted += ClientDownloadStringCompleted; 
    } 

    private void btn1_Click(object sender, RoutedEventArgs e) 
    { 
    string url = "http://www.nu.nl/feeds/rss/algemeen.rss"; 

    this.client.DownloadStringAsync(new Uri(url, UriKind.Absolute)); 

    if (this.result != string.Empty && this.result != null) 
    { 
    this.txbSummery.Text = this.result; 
    } 
    } 

    private void ClientDownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e) 
    { 
    this.result = e.Result; 
    //handle the response. 
    } 
} 

它给了我一个运行时错误按下按钮后：

微软JScript运行时错误：在Silverlight应用程序处理错误的操作过程中出现的异常，使结果无效。检查异常详情的InnerException。在System.ComponentModel.AsyncCompletedEventArgs.RaiseExceptionIfNecessary（） 在System.Net.DownloadStringCompletedEventArgs.get_Result（） 在JWTG.MainPage.ClientDownloadStringCompleted（对象发件人，DownloadStringCompletedEventArgs E） 在System.Net.WebClient.OnDownloadStringCompleted（DownloadStringCompletedEventArgs E） 在System.Net.WebClient.DownloadStringOperationCompleted（Object arg）

我试过很多东西，但都失败了。

我在想什么？还是有人知道我能以不同的方式实现这一目标？

在此先感谢！

Answer 1

这与clientaccesspolicy.xml相关。在这里阅读更多： http://msdn.microsoft.com/en-us/library/cc645032(VS.95).aspx

"If the connection request was from a WebClient or an HTTP class to a cross-domain site, the Silverlight runtime tries to download the security policy file using the HTTP protocol. The Silverlight runtime first tries to download a Silverlight policy file with a name of "clientaccesspolicy.xml" at the root of the requested target domain using the HTTP protocol.

If the "clientaccesspolicy.xml" is either not found (the web request returns a 404 status code), returned with an unexpected mime-type, is not valid XML, or has an invalid root node, then the Silverlight runtime will issue a request for a for the Flash policy file with a name of "crossdomain.xml" at the root of the requested target domain, using the HTTP protocol.

HTTP redirects for the policy file are not allowed. A redirect for a policy file will result in a SecurityException of access denied."

Answer 2

在这一行

this.client.DownloadStringAsync(new Uri(url, UriKind.Absolute)); 

你，说明在后台线程的asynchroneous下载。在接下来的一行中，你会以某种方式期待它已经完成？

如果您对Threading没有任何了解，请先尝试使用DownloadString。那么你的代码将工作。

Answer 3

试试这个，而不是你的btn1_Click和ClientDownloadStringCompleted方法。它在下载提要后更新文本框后调用GUI线程。如果因网络错误而失败，它将解压该异常（包含在TargetInvocationException中的内部异常）并重新抛出内部异常。

private void btn1_Click(object sender, RoutedEventArgs e) 
{ 
    string url = "http://www.nu.nl/feeds/rss/algemeen.rss"; 

    this.client.DownloadStringAsync(new Uri(url)); 
} 

private void ClientDownloadStringCompleted(object sender, 
         DownloadStringCompletedEventArgs e) 
{ 
    try 
    { 
     Dispatcher.BeginInvoke(() => this.txbSummery.Text = e.Result ?? ""); 
    } 
    catch (TargetInvocationException tiex) 
    { 
     throw tiex.InnerException; 
    } 
} 

如果错误再次发生（我猜会发生），请在这里发布堆栈跟踪和错误消息。

Answer 4

你试试吧

private void btn1_Click(object sender, RoutedEventArgs e) 
    { 
     string url = "http://www.nu.nl/feeds/rss/algemeen.rss"; 

     this.client.DownloadStringAsync(new Uri(url, UriKind.Absolute)); 

    } 

    private void ClientDownloadStringCompleted(object sender, DownloadStringCompletedEventArgs e) 
    { 
     Stream s = e.Result; 
     StreamReader strReader = new StreamReader(s); 
     string webContent = strReader.ReadToEnd(); 
     s.Close(); 
     this.txbSummery.Text =webContent; 

    }