Silverlight——Silverlight请求HttpHandler获取数据

在Silverlight里面调用WebServices和WCF是一件麻烦的事，在开发的时候，如果IP更改了，总是需要重配或者更新。虽然可以动态绑定，但是IP还是要配吧，而且性能比写死的要慢很多。而且，还得在根目录加上跨域XML。那么有什么解决方案呢？

比如有这么一个需求，当用户选择文件后，需要查询数据库获取是否可上传，以及上传的最大限制。由于以上原因，不愿意使用WebServices或者WCF来获取数据，于是首先想到的是写在initParams参数里面，但是不够理想，如果设置比较多，或者有更多自定义的条件的话，不太好处理。接下来就想到了利用ASP.NET里面的一般处理程序，具体操作如下：

1）在initParams配置参数“UploadHandlerName=Ajax/HttpUploadHandler.ashx”。

2）在Silverlight程序中的添加文件的方法中编写请求代码。这块值得注意的，一是路径，二是获取到数据后，要使用this.Dispatcher.BeginInvoke来更新界面（否则会出异常）。具体代码如下：

    public class RequestStates
    {
        /// <summary>
        /// 当前请求
        /// </summary>
        public HttpWebRequest CurrentWebRequest { get; set; }
        /// <summary>
        /// 当前用户文件
        /// </summary>
        public UserFile CurrentUserFile { get; set; }
    }

        private void AddFile(FileInfo file)
        {
            string fileName = file.Name;
            var userFile = new UserFile { FileName = file.Name, FileStream = file.OpenRead() };

            if (!string.IsNullOrEmpty(Configuration.Instance.CheckExtensionsHandlerName))
            {
                //获取处理的Handler类的路径
                UriBuilder httpHandlerUrlBuilder = new UriBuilder(new CustomUri(Configuration.Instance.CheckExtensionsHandlerName));
                //设置请求的参数
                httpHandlerUrlBuilder.Query = string.Format("{2}file={0}&Extension={1}", HttpUtility.UrlEncode(userFile.FileName), HttpUtility.UrlEncode(Path.GetExtension(userFile.FileName)), string.IsNullOrEmpty(httpHandlerUrlBuilder.Query) ? string.Empty : httpHandlerUrlBuilder.Query.Remove(0, 1) + "&");
                //创建请求
                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(httpHandlerUrlBuilder.Uri);
                request.Method = "POST";
                //设置自定义信息，用于异步请求
                var requestStates = new RequestStates()
                                         {
                                             CurrentUserFile = userFile,
                                             CurrentWebRequest = request
                                         };
                //开始异步请求
                request.BeginGetRequestStream(new AsyncCallback(RequestReady), requestStates);
            }
            else
            {
                _files.Add(userFile);
            }
        }

        private void RequestReady(IAsyncResult asynchronousResult)
        {
            var requestStates = (RequestStates)asynchronousResult.AsyncState;
            HttpWebRequest webRequest = requestStates.CurrentWebRequest;
            Stream requestStream = webRequest.EndGetRequestStream(asynchronousResult);
            requestStream.Close();
            webRequest.BeginGetResponse(new AsyncCallback(ResponseReady), requestStates);
        }
        void ResponseReady(IAsyncResult asyncResult)
        {
            var requestStates = (RequestStates)asyncResult.AsyncState;
            HttpWebRequest webRequest = requestStates.CurrentWebRequest;
            var userFile = requestStates.CurrentUserFile;
            var webResponse = (HttpWebResponse)webRequest.EndGetResponse(asyncResult);
            var reader = new StreamReader(webResponse.GetResponseStream());
            //获取Httphandler类返回的数据
            string responsestring = reader.ReadToEnd();
            reader.Close();
            decimal maxSize = Convert.ToDecimal(responsestring);
            //Check for the file size limit (configurable)
            if (maxSize == 0 || (userFile.FileStream.Length / 1024) <= maxSize)
            {
                this.Dispatcher.BeginInvoke(
                    () => _files.Add(userFile)
                    );

            }
            else if (maxSize < 0)
            {
                this.Dispatcher.BeginInvoke(
                    delegate()
                    {
                        var messageWindow = new MessageChildWindow
                                                               {
                                                                   Message =
                                                                       string.Format("不允许上传{0}类文件！",
                                                                                     Path.GetExtension(userFile.FileName))
                                                               };
                        messageWindow.Show();

                        if (MaximumFileSizeReached != null)
                            MaximumFileSizeReached(this, null);
                    });
            }
            else
            {
                this.Dispatcher.BeginInvoke(
                    () =>
                    {
                        var messageWindow = new MessageChildWindow
                                                {
                                                    Message =
                                                        string.Format("{0}{1}{2}KB.",
                                                                      Path.GetExtension(userFile.FileName),
                                                                      UserMessages.MaxFileSize, (maxSize).ToString())
                                                };
                        messageWindow.Show();

                        if (MaximumFileSizeReached != null)
                            MaximumFileSizeReached(this, null);
                    });
            }
        }

效果如下：