xml – 如何在Silverlight中评估XPath表达式？

第一：

在Web项目中创建一个通用处理程序.使用以下代码为ProcessRequest添加ASHX文件(为简洁起见,简化)：

public void ProcessRequest(HttpContext context)
    {
        context.Response.ContentType = "text/plain";

        string xml = context.Request.Form["xml"].ToString();
        string xpath = context.Request.Form["xpath"].ToString();

        XmlReader reader = new XmlTextReader(new StringReader(xml));
        XDocument doc = XDocument.Load(reader);

        var rawResult = doc.XPathEvaluate(xpath);
        string result = String.Empty;
        foreach (var r in ((IEnumerable<object>)rawResult)) 
        {
            result += r.ToString();
        }

        context.Response.Write(result);

    }

应该注意的是,对于xml处理,您需要引用一些名称空间：

> System.IO
> System.Xml
> System.Xml.XPath
> System.Xml.Linq

第二：

您需要一些代码来允许您向通用处理程序发出异步帖子.下面的代码很长,但基本上你通过以下代码：

>您的通用处理程序的Uri
>键值对的字典(假设xml文档和xpath)
>成功和失败的回调
>对UserControl的调度计时器的引用,以便您可以在回调中访问UI(如有必要).

以下是我在实用程序类中放置的一些代码：

public class WebPostHelper
{
    public static void GetPostData(Uri targetURI,Dictionary<string,string> dataDictionary,Action<string> onSuccess,Action<string> onError,Dispatcher threadDispatcher)
    {
        var postData = String.Join("&",dataDictionary.Keys.Select(k => k + "=" + dataDictionary[k]).ToArray());

        WebRequest requ = HttpWebRequest.Create(targetURI);
        requ.Method = "POST";
        requ.ContentType = "application/x-www-form-urlencoded";
        var res = requ.BeginGetRequestStream(new AsyncCallback(
            (ar) =>
            {
                Stream stream = requ.EndGetRequestStream(ar);
                StreamWriter writer = new StreamWriter(stream);
                writer.Write(postData);
                writer.Close();
                requ.BeginGetResponse(new AsyncCallback(
                        (ar2) =>
                        {
                            try
                            {
                                WebResponse respStream = requ.EndGetResponse(ar2);
                                Stream stream2 = respStream.GetResponseStream();
                                StreamReader reader2 = new StreamReader(stream2);
                                string responseString = reader2.ReadToEnd();
                                int spacerIndex = responseString.IndexOf('|') - 1;
                                string status = responseString.Substring(0,spacerIndex);
                                string result = responseString.Substring(spacerIndex + 3);
                                if (status == "success")
                                {
                                    if (onSuccess != null)
                                    {
                                        threadDispatcher.BeginInvoke(() =>
                                        {
                                            onSuccess(result);
                                        });
                                    }
                                }
                                else
                                {
                                    if (onError != null)
                                    {
                                        threadDispatcher.BeginInvoke(() =>
                                        {
                                            onError(result);
                                        });
                                    }
                                }
                            }
                            catch (Exception ex)
                            {
                                string data2 = ex.ToString();
                            }
                        }
                    ),null);

            }),null);
    }
}

第三：

调用实用程序类并传递xml和xpath：

private void testButton_Click(object sender,RoutedEventArgs e)
    {
        Dictionary<string,string> values = new Dictionary<string,string>();
        values.Add("xml","<Foo />");
        values.Add("xpath","/*");

        //Uri uri = new Uri("http://eggs/spam.ashx");
        Uri uri = new Uri("http://localhost:3230/xPathHandler.ashx");

        WebPostHelper.GetPostData(uri,values,(result) =>
            {
                MessageBox.Show("Your result " + result);
            },(errMessage) =>
            {
                MessageBox.Show("An error " + errMessage);
            },this.Dispatcher);

    }

让我重申,为简洁起见,此处的代码已经简化.您可能希望使用序列化程序将更复杂的类型传递给通用处理程序.当您从context.Request.Form集合中获取值时,您将需要以防御方式编写无效的“健全性检查”.但基本思想如上所述.