Question

        XmlDocument studentData;
        XmlNodeList studentList;
        TotalClass totalClass = null;
        string gender = "";

        studentData = new XmlDocument();
                studentData.LoadXml("<root>"
                    + "<STUDNT ID=\"7\" Gender=\"M\"></STUDNT>"
                    + "<STUDNT ID=\"16\" Gender=\"F\"></STUDNT>"
                    + "<STUDNT ID=\"22\" Gender=\"F\"></STUDNT>"
                    + "<STUDNT ID=\"25\" Gender=\"M\"></STUDNT>"
                    + "<STUDNT ID=\"27\" Gender=\"F\"></STUDNT>"
                    + "<STUDNT ID=\"32\" Gender=\"M\"></STUDNT>"
                    + "<STUDNT ID=\"35\" Gender=\"f\"></STUDNT>"
                    + "<STUDNT ID=\"45\" Gender=\"M\"></STUDNT>"
                    + "<STUDNT ID=\"4423453244\" Gender=\"F\"></STUDNT>"
                    + "<STUDNT ID=\"44344\" Gender=\"F\"></STUDNT>"
                    + "</root>");

        studentList = studentData.SelectNodes("//STUDENT");
        if(studentList != null && studentList.Count > 0)
        {
            foreach(XmlElement student in studentList)
            {
                gender = student.GetAttribute("Gender");
                switch(gender)
                {
                    case "F":
                        totalClass.Females++;   
                        break;

                    default:
                    case "M":
                        totalClass.Males++;                           
                        break;
                }

            }// end loop


        }

        this.lblMales.Text = totalClass.Males.ToString ();      
        this.lblFemale.Text = totalClass.Females.ToString();
        this.lblTotal.Text = (totalClass.Females + totalClass.Males).ToString();

我需要一些这方面的帮助。我被分配调试这个程序，我找不到解决方法。点击计数按钮后继续获取NullReferenceException。

Answer 1

您的totalClass对象为空。在你的foreach之前，宣布你的课程。你可以默认使用它。

studentList = studentData.SelectNodes("//STUDENT");
totalClass = new TotalClass();//add this.

阅读这个问题，它几乎是堆栈溢出中C＃的着名问题： What is a NullReferenceException, and how do I fix it?

Answer 2

尝试像这样修改

studentList = studentData.SelectNodes（＆＃34; / root / STUDNT＆＃34;）;

并修改为

totalClass = new TotalClass（）;

在文本框控件中显示xml文件

2 个答案: