引发异常的简单表单应用程序

本文关键字：表单 应用程序 简单 异常 | 更新日期: 2023-09-27 17:55:54

当按下"计数"按钮时，此应用程序显示XML文档中的女性，男性和学生总数。 问题是程序按下"计数"按钮时引发错误，我不确定为什么？其次，我不确定这三个总数是否正确。我对编程很陌生，如果可能的话，我希望得到一些帮助。

namespace DebugSession
{
    /// <summary>
    /// Summary description for Form1.
    /// </summary>
    public class Form1 : System.Windows.Forms.Form
    {
        private System.Windows.Forms.Label label1;
        private System.Windows.Forms.Label lblTotal;
        private System.Windows.Forms.Label label4;
        private System.Windows.Forms.Label lblMales;
        private System.Windows.Forms.Label lbl;
        private System.Windows.Forms.Button btnCount;
        private System.Windows.Forms.Label lblFemale;
        /// <summary>
        /// Required designer variable.
        /// </summary>
        private System.ComponentModel.Container components = null;
      public Form1()
      {
         //
         // Required for Windows Form Designer support
         //
        InitializeComponent();
         //
         // TODO: Add any constructor code after InitializeComponent call
         //
       }
         /// <summary>
         /// Clean up any resources being used.
         /// </summary>
      protected override void Dispose( bool disposing )
      {
        if( disposing )
        {
            if (components != null) 
            {
                components.Dispose();
            }
        }
        base.Dispose( disposing );
      }
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main() 
    {
        Application.Run(new Form1());
    }
    private void label1_Click(object sender, System.EventArgs e)
    {

    }
    private void btnCount_Click(object sender, System.EventArgs e)
    {
        XmlDocument studentData = null;
        XmlNodeList studentList = null;
        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();

    }//btnCount_Click
}
}

我还有一个总类

using System;
namespace DebugSession
{
    /// <summary>
/// Summary description for TotalClass.
/// </summary>
public class TotalClass
 {
    /// <summary>
    /// Gets and Sets number of males
    /// </summary>
   public int Males
    {
        set{this.males = value;}
        get{return this.males;}
    }
    private int males = -1;
    /// <summary>
    /// Gets and Sets number of females
    /// </summary>
    public int Females
    {
        set{this.females = value;}
        get{return this.females;}
    }
    private int females = -1;
}//end class
}`

引发异常的简单表单应用程序

你的代码中有很多问题：

首先：您搜索元素"STUDENT"，但您的XML包含"STUDNT"。这会导致跳过整个循环并直接跳转到标签文本设置（这会导致后续NullReferenceException ）

第二：你不能在不实例化的情况下使用类的实例 

 TotalClass totalClass = new TotalClass();

第三：您切换为大写"F"和"M"，但其中一个 xml 元素具有小写"f"。这会导致该条目计为男性，因为默认值与"M"大小写耦合。将交换机更改为 

switch(gender.ToUpper())

第四：TotalClass将女性和男性的计数器初始化为 -1，当然这会导致不正确的结果，将其更改为 

 private int males = 0;
 private int females = 0;

更改：

TotalClass totalClass = null;

自：

TotalClass totalClass = new TotalClass();
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