c#之使用 Web 服务遍历 Sharepoint 列表项的属性，得到 "Object reference not set to an instance of an object"

我正在使用 C# 调用 Sharepoint 网络服务。我想获得一个 Sharepoint 列表，然后针对列表中的每个项目，将其属性写入控制台。当我使用 foreach 遍历属性时，我不断收到“未设置对象实例的对象引用”。代码如下:

class Program 
    { 
        static void Main(string[] args) 
        { 
            try 
            {                  
                cSharpTest_service.Lists lists = new cSharpTest_service.Lists(); 
                lists.Url = "http://wsssandbox/sites/cSharp/_vti_bin/lists.asmx"; 
                lists.Credentials = System.Net.CredentialCache.DefaultCredentials; 
                System.Xml.XmlNode listData = lists.GetListItems("cSharpTestList", "", null, null, "", null, ""); 
 
 
 
                foreach (System.Xml.XmlNode iterateNode in listData) 
                { 
 
                    Console.WriteLine("--NODE--"); 
                    System.Xml.XmlAttributeCollection attrs = iterateNode.Attributes; 
                    foreach (System.Xml.XmlAttribute attr in attrs) 
                    { 
                        Console.WriteLine("Name:"); 
                        Console.WriteLine(attr.Name); 
                        Console.WriteLine("Value:"); 
                        Console.WriteLine(attr.Value); 
                    } 
 
                } 
                Console.ReadLine(); 
 
            } 
            catch (Exception e) 
            { 
                Console.WriteLine(e.Message); 
                Console.ReadLine(); 
            } 
 
 
        } 
      } 

我认为它抛出异常是因为某些列表项的某些属性为 Null。但是我不知道如何在 foreach 迭代中检查属性是否为 null。

请您参考如下方法:

看看这个例子和这个 article .

public void getListData() 
{ 
  WS_Lists.Lists myservice = new WS_Lists.Lists(); 
  myservice.Credentials = System.Net.CredentialCache.DefaultCredentials; 
  myservice.Url = "http://merdev-moss:5050/testsara/_vti_bin/Lists.asmx"; 
 
  try 
  { 
    /* Assign values to pass the GetListItems method*/ 
    string listName = "{5C65CB1A-2E1B-488A-AC07-B115CD0FC647}"; 
    string viewName = "{75E689B4-5773-43CB-8324-58E42E1EB885}"; 
    string rowLimit = "100"; 
 
    // Instantiate an XmlDocument object 
    System.Xml.XmlDocument xmlDoc = new System.Xml.XmlDocument(); 
    System.Xml.XmlElement query = xmlDoc.CreateElement("Query"); 
    System.Xml.XmlElement viewFields = xmlDoc.CreateElement("ViewFields"); 
    System.Xml.XmlElement queryOptions = xmlDoc.CreateElement("QueryOptions"); 
 
    /*Use CAML query*/ 
    query.InnerXml = "<Where><Gt><FieldRef Name=\"ID\" />" + 
    "<Value Type=\"Counter\">0</Value></Gt></Where>"; 
    viewFields.InnerXml = "<FieldRef Name=\"Title\" />"; 
    queryOptions.InnerXml = ""; 
 
    System.Xml.XmlNode nodes = myservice.GetListItems(listName, viewName, query, viewFields, rowLimit, null, null); 
 
    foreach (System.Xml.XmlNode node in nodes) 
    { 
        if (node.Name == "rs:data") 
        { 
            for (int i = 0; i < node.ChildNodes.Count; i++) 
            { 
                if (node.ChildNodes[i].Name == "z:row") 
                { 
                    Response.Write(node.ChildNodes[i].Attributes["ows_Title"].Value + "</br>"); 
                } 
            } 
        } 
    } 
} 
 catch (Exception ex) 
 { 
    Response.Write(ex.Message); 
 } 
}