public class Container : XmlElementGenerator{    public string projectcode { get; set; }    public string projectname { get; set; }    public string projectleader { get; set; }    public string barcode { get; set; }    public string sampleartid { get; set; }    public string sampledescription { get; set; }    public string remark { get; set; }    public DateTime samplingdate { get; set; }    public int samplenumber { get; set; }    public XmlElement GenerateXMLElement(XmlDocument xmlDocument)    {        Type containerGenerator = typeof(Container);        XmlElement container = ElementChildrenGenerator(xmlDocument, "container");        foreach (PropertyInfo prop in containerGenerator.GetProperties())        {            container.AppendChild(ElementChildrenGenerator(xmlDocument, prop.Name, prop.GetValue(this).ToString()));        }        return container;    }}此處出現(xiàn)錯誤prop.GetValue(this)-“ System.NullReferenceException：對象引用未設(shè)置為對象的實例”。為什么我不能使用“ this”來訪問對象？我不想再添加一個參數(shù)。請幫助