c# - 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"

Question

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。

Answer 1

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);
 }
}