C＃XML解析錯誤：未將對象引用設置爲對象實例

Question

我試圖獲取下面XML結構中的<d:neu_UniqueId>和<d:Name>元素的值。我正在處理的程序調用WCF Web服務，並根據用戶輸入的搜索條件返回一個包含此信息列表的XML文檔（我已經刪除了隱私值）。

<entry> 
<id xmlns=\"http://www.w3.org/2005/Atom\">http://quahildy01/xRMDRMA02/XRMServices/2011/OrganizationData.svc</id> 
<title type=\"text\" xmlns=\"http://www.w3.org/2005/Atom\">somethingHere</title> 
<updated xmlns=\"http://www.w3.org/2005/Atom\">2013-04-24T17:15:45Z</updated> 
<author xmlns=\"http://www.w3.org/2005/Atom\"><name /></author> 
<link rel=\"edit\" title=\"Account\" href=\"AccountSet(guid'aa2232f4-418a-e111-9710-005056a8161c')\" xmlns=\"http://www.w3.org/2005/Atom\" /> 
<category term=\"Microsoft.Crm.Sdk.Data.Services.Account\" scheme=\"http://schemas.microsoft.com/ado/2007/08/dataservices/scheme\" xmlns=\"http://www.w3.org/2005/Atom\" /> 
<content type=\"application/xml\" xmlns=\"http://www.w3.org/2005/Atom\"> 
    <m:properties xmlns:m=\"http://schemas.microsoft.com/ado/2007/08/dataservices/metadata\"> 
     <d:neu_UniqueId xmlns:d=\"http://schemas.microsoft.com/ado/2007/08/dataservices\">123</d:neu_UniqueId> 
     <d:AccountId m:type=\"Edm.Guid\" xmlns:d=\"http://schemas.microsoft.com/ado/2007/08/dataservices\">1</d:AccountId> 
     <d:Name xmlns:d=\"http://schemas.microsoft.com/ado/2007/08/dataservices\">SomethingInHere</d:Name> 
    </m:properties> 
</content> 
</entry> 

這是我正在使用的C＃代碼。當我通過代碼，我可以看到正確的值在childNode變量，然而，當在所述第一.InnerText()方法的程序I移動接收到此錯誤：

NullReferenceException: Object reference not set to an instance of an object. 

這裏是代碼

 try 
     { 
      WebRequest myWebRequest = WebRequest.Create(URL); 
      myWebRequest.PreAuthenticate = true; 
      myWebRequest.Credentials = System.Net.CredentialCache.DefaultCredentials; 

      WebResponse myWebResponse = myWebRequest.GetResponse(); 
      Stream myFileStreamResult = myWebResponse.GetResponseStream(); 
      Encoding encoder = System.Text.Encoding.GetEncoding("utf-8"); 
      StreamReader readStream = new StreamReader(myFileStreamResult, encoder); 

      results = readStream.ReadToEnd(); 

      XmlDocument xmlDoc = new XmlDocument(); 
      xmlDoc.LoadXml(results); 

      XmlNodeList parentNode = xmlDoc.GetElementsByTagName("entry"); 

      XmlNamespaceManager nsmgr = new XmlNamespaceManager(xmlDoc.NameTable); 
      nsmgr.AddNamespace("m", "http://schemas.microsoft.com/ado/2007/08/dataservices/metadata"); 
      nsmgr.AddNamespace("d", "http://schemas.microsoft.com/ado/2007/08/dataservices"); 

      string accountName2 = xmlDoc.SelectSingleNode("entry/content/m:properties/d:Name", nsmgr).InnerText; 

      foreach (XmlNode childNode in parentNode) 
      { 
       string accountName = childNode.SelectSingleNode("/content/m:properties/d:Name", nsmgr).InnerText; 
       string uniqueId = childNode.SelectSingleNode("/content/m:properties/d:neu_UniqueId", nsmgr).InnerText; 
      } 

     } 

編輯

看起來像這是從Web服務返回XML的問題。對於每個元素，xmlns屬性包含值前的\字符。

Answer 1

嘗試添加「http://www.w3.org/2005/Atom」的名稱空間條目並在XPath中使用它。還要在foreach中的SelectSingleNode調用中從XPath中刪除第一個'/'字符。

編輯

我安裝在一個文件名爲response.xml的XML，它看起來像下面這樣。刪除你的一些反斜槓，使其可行。

<?xml version="1.0" encoding="UTF-8"?> 
<entry> 
    <id xmlns="http://www.w3.org/2005/Atom">http://quahildy01/xRMDRMA02/XRMServices/2011/OrganizationData.svc</id> 
    <title type="text" xmlns="http://www.w3.org/2005/Atom">somethingHere</title> 
    <updated xmlns="http://www.w3.org/2005/Atom">2013-04-24T17:15:45Z</updated> 
    <author xmlns="http://www.w3.org/2005/Atom"> 
    <name /> 
    </author> 
    <link rel="edit" title="Account" href="AccountSet(guid'aa2232f4-418a-e111-9710-005056a8161c')" xmlns="http://www.w3.org/2005/Atom" /> 
    <category term="Microsoft.Crm.Sdk.Data.Services.Account" scheme="http://schemas.microsoft.com/ado/2007/08/dataservices/scheme" xmlns="http://www.w3.org/2005/Atom" /> 
    <content type="application/xml" xmlns="http://www.w3.org/2005/Atom"> 
    <m:properties xmlns:m="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata"> 
     <d:neu_UniqueId xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices">123</d:neu_UniqueId> 
     <d:AccountId m:type="Edm.Guid" xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices">1</d:AccountId> 
     <d:Name xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices">SomethingInHere</d:Name> 
    </m:properties> 
    </content> 
</entry> 

我在文件中讀取，並用下面的代碼解析它，它爲我工作。

 string path = @"response.xml"; 
     XmlDocument xmlDoc = new XmlDocument(); 
     xmlDoc.Load(path); 

     XmlNodeList parentNode = xmlDoc.GetElementsByTagName("entry"); 

     XmlNamespaceManager nsmgr = new XmlNamespaceManager(xmlDoc.NameTable); 
     nsmgr.AddNamespace("f", "http://www.w3.org/2005/Atom"); 
     nsmgr.AddNamespace("m", "http://schemas.microsoft.com/ado/2007/08/dataservices/metadata"); 
     nsmgr.AddNamespace("d", "http://schemas.microsoft.com/ado/2007/08/dataservices"); 

     var accountName2 = xmlDoc.SelectSingleNode("entry/f:content/m:properties/d:Name", nsmgr).InnerText; 

     foreach (XmlNode childNode in parentNode) 
     { 
      string accountName = childNode.SelectSingleNode("f:content/m:properties/d:Name", nsmgr).InnerText; 
      string uniqueId = childNode.SelectSingleNode("f:content/m:properties/d:neu_UniqueId", nsmgr).InnerText; 
     }