在Silverlight中使用WebClient 下载资源时存在缓存问题的解决方案

问题：

      在Silverlight中使用WebClient 下载资源时，存在缓存问题。当资源更新的时候，下载后的内容未更新。

解决方案一：

     既然资源的下载依赖于URL，可以动态改变URL，来获取最新的资源。

      public void LoadStringresource(String relativeFileName)
        {
            WebClient xmlClient = new WebClient();
            xmlClient.Encoding = System.Text.Encoding.Unicode;
            xmlClient.DownloadStringCompleted += new DownloadStringCompletedEventHandler(XMLFileLoaded);
            relativeFilename = relativeFilename +"?eking=" + random.Next().ToString();
            xmlClient.DownloadStringAsync(new Uri(relativeFileName));
        }

        void XMLFileLoaded(object sender,DownloadStringCompletedEventArgs E)
        {
            if (e.Error == null)
            {
                fileData = e.Result;

                SampleDrawings = new DrawingStorage(fileData);
                drawingXml = SampleDrawings.Storage;
                if (drawingXml != null)
                {
                    loadDrawing(drawingXml,isRunModE);
                }
            }
        }

                                                               EKING/王毅，2009,TPRI 版本所有。

解决方案二：

将下面的代码加到  silverlight 库中或直接加在应用程序中。

    public static class WebClientextensions
    {
        public static void DownloadStringAsync(this WebClient client,Uri uri,object user_token,bool fresh_copy)
        {
            if (!fresh_copy)
            {
                client.DownloadStringAsync(uri,user_token);
            }
            else
            {
                client.DownloadStringAsync(new Uri(uri.AbsoluteUri + "?" + Guid.NewGuid().ToString()),user_token);
            }
        }
    }
}