该项目编译完美，但我得到一个未处理的异常，而且不知道为什么

Question

我得到一个未处理的异常，说：

System.NullReferenceException: Object reference not set to an instance of an object. 
at Eagle_Eye_Class_Finder.GetSchedule.GetDataFromNumber(String ID) in C:\Users\Joshua Banks\Desktop\EET Project\Eagle Eye Class Finder\GetSchedule.cs:line 24 
at Eagle_Eye_Class_Finder.Form1.button2_Click(Object sender, EventArgs e) in C:\Users\Joshua Banks\Desktop\EET Project\Eagle Eye Class Finder\Form1.cs:line 196 
at System.Windows.Forms.Control.OnClick(EventArgs e) 
at System.Windows.Forms.Button.OnClick(EventArgs e) 
at System.Windows.Forms.Button.PerformClick() 
at System.Windows.Forms.Form.ProcessDialogKey(Keys keyData) 
at System.Windows.Forms.Control.ProcessDialogKey(Keys keyData) 
at System.Windows.Forms.TextBoxBase.ProcessDialogKey(Keys keyData) 
at System.Windows.Forms.Control.PreProcessMessage(Message& msg) 
at System.Windows.Forms.Control.PreProcessControlMessageInternal(Control target, Message& msg) 
at System.Windows.Forms.Application.ThreadContext.PreTranslateMessage(MSG& msg) 

这里是我的GET时间表类：

using System; 
using System.IO; 
using System.Data; 
using System.Text; 
using System.Drawing; 
using System.Data.OleDb; 
using System.Collections; 
using System.ComponentModel; 
using System.Windows.Forms; 
using System.Drawing.Printing; 
using System.Collections.Generic; 

namespace Eagle_Eye_Class_Finder 
{ 
    public class GetSchedule 
    { 
     public string GetDataFromNumber(string ID) 
     { 
      IDnumber[] IDnumbers = new IDnumber[3]; 
      foreach (IDnumber IDCandidateMatch in IDnumbers) 
      { 
       if (IDCandidateMatch.ID == ID) 
       { 
        StringBuilder myData = new StringBuilder(); 
        myData.AppendLine(IDCandidateMatch.Name); 
        myData.AppendLine(": "); 
        myData.AppendLine(IDCandidateMatch.ID); 
        myData.AppendLine(IDCandidateMatch.year); 
        myData.AppendLine(IDCandidateMatch.class1); 
        myData.AppendLine(IDCandidateMatch.class2); 
        myData.AppendLine(IDCandidateMatch.class3); 
        myData.AppendLine(IDCandidateMatch.class4); 
        //return myData; 
        return myData.ToString(); 
       } 
      } 
      return ""; 
     } 

     public GetSchedule() 
     { 
      IDnumber[] IDnumbers = new IDnumber[3]; 
      IDnumbers[0] = new IDnumber() { Name = "Joshua Banks", ID = "900456317", year = "Senior", class1 = "TEET 4090", class2 = "TEET 3020", class3 = "TEET 3090", class4 = "TEET 4290" }; 
      IDnumbers[1] = new IDnumber() { Name = "Sean Ward", ID = "900456318", year = "Junior", class1 = "ENGNR 4090", class2 = "ENGNR 3020", class3 = "ENGNR 3090", class4 = "ENGNR 4290" }; 
      IDnumbers[2] = new IDnumber() { Name = "Terrell Johnson", ID = "900456319", year = "Sophomore", class1 = "BUS 4090", class2 = "BUS 3020", class3 = "BUS 3090", class4 = "BUS 4290" }; 
     } 

     public class IDnumber 
     { 
      public string Name { get; set; } 
      public string ID { get; set; } 
      public string year { get; set; } 
      public string class1 { get; set; } 
      public string class2 { get; set; } 
      public string class3 { get; set; } 
      public string class4 { get; set; } 

      public static void ProcessNumber(IDnumber myNum) 
      { 
       StringBuilder myData = new StringBuilder(); 
       myData.AppendLine(myNum.Name); 
       myData.AppendLine(": "); 
       myData.AppendLine(myNum.ID); 
       myData.AppendLine(myNum.year); 
       myData.AppendLine(myNum.class1); 
       myData.AppendLine(myNum.class2); 
       myData.AppendLine(myNum.class3); 
       myData.AppendLine(myNum.class4); 
       MessageBox.Show(myData.ToString()); 
      } 
     } 
    } 
} 

这里我的表1类：

using System; 
using System.IO; 
using System.Data; 
using System.Text; 
using System.Drawing; 
using System.Data.OleDb; 
using System.Collections; 
using System.Windows.Forms; 
using System.ComponentModel; 
using System.Drawing.Printing; 
using System.Collections.Generic; 

namespace Eagle_Eye_Class_Finder 
{ 
    /// This form is the entry form, it is the first form the user will see when the app is run. 
    /// 

    public class Form1 : System.Windows.Forms.Form 
    { 
     private System.Windows.Forms.TextBox textBox1; 
     private System.Windows.Forms.ProgressBar progressBar1; 
     private System.Windows.Forms.PictureBox pictureBox1; 
     private System.Windows.Forms.Button button2; 
     private System.Windows.Forms.DateTimePicker dateTimePicker1; 
     private IContainer components; 
     private Timer timer1; 
     private BindingSource form1BindingSource; 
     public static Form Mainform = null; 

     // creates new instance of second form 
     YOURCLASSSCHEDULE SecondForm = new YOURCLASSSCHEDULE(); 

     public Form1() 
     { 
      InitializeComponent(); 

      // TODO: Add any constructor code after InitializeComponent call 

     } 

     /// Clean up any resources being used. 

     protected override void Dispose(bool disposing) 
     { 
      if (disposing) 
      { 
       if (components != null) 
       { 
        components.Dispose(); 
       } 
      } 
      base.Dispose(disposing); 
     } 

     #region Windows Form Designer generated code 
     /// <summary> 
     /// Required method for Designer support - do not modify 
     /// the contents of this method with the code editor. 
     /// </summary> 
     private void InitializeComponent() 
     { 
      this.components = new System.ComponentModel.Container(); 
      System.ComponentModel.ComponentResourceManager resources = new System.ComponentModel.ComponentResourceManager(typeof(Form1)); 
      this.textBox1 = new System.Windows.Forms.TextBox(); 
      this.progressBar1 = new System.Windows.Forms.ProgressBar(); 
      this.pictureBox1 = new System.Windows.Forms.PictureBox(); 
      this.button2 = new System.Windows.Forms.Button(); 
      this.dateTimePicker1 = new System.Windows.Forms.DateTimePicker(); 
      this.timer1 = new System.Windows.Forms.Timer(this.components); 
      this.form1BindingSource = new System.Windows.Forms.BindingSource(this.components); 
      ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).BeginInit(); 
      ((System.ComponentModel.ISupportInitialize)(this.form1BindingSource)).BeginInit(); 
      this.SuspendLayout(); 
      // 
      // textBox1 
      // 
      this.textBox1.BackColor = System.Drawing.SystemColors.ActiveCaption; 
      this.textBox1.DataBindings.Add(new System.Windows.Forms.Binding("Text", this.form1BindingSource, "Text", true, System.Windows.Forms.DataSourceUpdateMode.OnValidation, null, "900456317")); 
      this.textBox1.Location = new System.Drawing.Point(328, 280); 
      this.textBox1.Name = "textBox1"; 
      this.textBox1.Size = new System.Drawing.Size(208, 20); 
      this.textBox1.TabIndex = 2; 
      this.textBox1.TextChanged += new System.EventHandler(this.textBox1_TextChanged); 
      // 
      // progressBar1 
      // 
      this.progressBar1.Location = new System.Drawing.Point(258, 410); 
      this.progressBar1.MarqueeAnimationSpeed = 10; 
      this.progressBar1.Name = "progressBar1"; 
      this.progressBar1.Size = new System.Drawing.Size(344, 8); 
      this.progressBar1.TabIndex = 3; 
      this.progressBar1.Click += new System.EventHandler(this.progressBar1_Click); 
      // 
      // pictureBox1 
      // 
      this.pictureBox1.BackColor = System.Drawing.SystemColors.ControlLightLight; 
      this.pictureBox1.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D; 
      this.pictureBox1.Image = ((System.Drawing.Image)(resources.GetObject("pictureBox1.Image"))); 
      this.pictureBox1.Location = new System.Drawing.Point(680, 400); 
      this.pictureBox1.Name = "pictureBox1"; 
      this.pictureBox1.Size = new System.Drawing.Size(120, 112); 
      this.pictureBox1.TabIndex = 4; 
      this.pictureBox1.TabStop = false; 
      this.pictureBox1.Click += new System.EventHandler(this.pictureBox1_Click); 
      // 
      // button2 
      // 
      this.button2.Font = new System.Drawing.Font("Mistral", 15.75F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0))); 
      this.button2.Image = ((System.Drawing.Image)(resources.GetObject("button2.Image"))); 
      this.button2.Location = new System.Drawing.Point(699, 442); 
      this.button2.Name = "button2"; 
      this.button2.Size = new System.Drawing.Size(78, 28); 
      this.button2.TabIndex = 5; 
      this.button2.Text = "OK"; 
      this.button2.Click += new System.EventHandler(this.button2_Click); 
      // 
      // dateTimePicker1 
      // 
      this.dateTimePicker1.Location = new System.Drawing.Point(336, 104); 
      this.dateTimePicker1.Name = "dateTimePicker1"; 
      this.dateTimePicker1.Size = new System.Drawing.Size(200, 20); 
      this.dateTimePicker1.TabIndex = 6; 
      this.dateTimePicker1.ValueChanged += new System.EventHandler(this.dateTimePicker1_ValueChanged); 
      // 
      // timer1 
      // 
      this.timer1.Tick += new System.EventHandler(this.timer1_Tick); 
      // 
      // form1BindingSource 
      // 
      this.form1BindingSource.DataSource = typeof(Eagle_Eye_Class_Finder.Form1); 
      // 
      // Form1 
      // 
      this.AcceptButton = this.button2; 
      this.AutoScaleBaseSize = new System.Drawing.Size(5, 13); 
      this.BackgroundImage = ((System.Drawing.Image)(resources.GetObject("$this.BackgroundImage"))); 
      this.BackgroundImageLayout = System.Windows.Forms.ImageLayout.Stretch; 
      this.ClientSize = new System.Drawing.Size(856, 556); 
      this.Controls.Add(this.dateTimePicker1); 
      this.Controls.Add(this.button2); 
      this.Controls.Add(this.pictureBox1); 
      this.Controls.Add(this.progressBar1); 
      this.Controls.Add(this.textBox1); 
      this.Name = "Form1"; 
      this.Text = "Eagle Eye Class Finder"; 
      this.Load += new System.EventHandler(this.Form1_Load); 
      ((System.ComponentModel.ISupportInitialize)(this.pictureBox1)).EndInit(); 
      ((System.ComponentModel.ISupportInitialize)(this.form1BindingSource)).EndInit(); 
      this.ResumeLayout(false); 
      this.PerformLayout(); 
     } 
     #endregion 

     /// The main entry point for the application. 

     [STAThread] 
     static void Main() 
     { 
      Application.Run(new Form1()); 

     } 

     public void Form1_Load(object sender, System.EventArgs e) 
     { 

     } 

     public void textBox1_TextChanged(object sender, System.EventArgs e) 
     { 
      //allows only numbers to be entered in textbox 
      string Str = textBox1.Text.Trim(); 
      double Num; 
      bool isNum = double.TryParse(Str, out Num); 

      if (isNum) 
       Console.ReadLine(); 
      else 
       MessageBox.Show("Enter A Valid ID Number!"); 
     } 

     public void button2_Click(object sender, System.EventArgs e) 
     { 
      string text = textBox1.Text; 
      Mainform = this; 

      this.Hide(); 

      GetSchedule myScheduleFinder = new GetSchedule(); 
      string result = myScheduleFinder.GetDataFromNumber(text); 

      if (!string.IsNullOrEmpty(result)) 
      { 
       MessageBox.Show(result); 
      } 
      else 
      { 
       MessageBox.Show("Enter A Valid ID Number!"); 
      } 
     } 

     public void dateTimePicker1_ValueChanged(object sender, System.EventArgs e) 
     { 

     } 

     public void pictureBox1_Click(object sender, System.EventArgs e) 
     { 

     } 

     public void progressBar1_Click(object sender, EventArgs e) 
     { 
      //this.progressBar1 = new System.progressBar1(); 
      //progressBar1.Maximum = 200; 
      //progressBar1.Minimum = 0; 
      //progressBar1.Step = 20; 
     } 

     private void timer1_Tick(object sender, EventArgs e) 
     { 
      //if (progressBar1.Value >= 200) 
      //{ 
      //progressBar1.Value = 0; 
      //} 
      //return; 
      //} 

      //progressBar1.Value != 20; 

     } 
    } 
} 

这里是我的表格2类：

using System; 
using System.Drawing; 
using System.Collections; 
using System.ComponentModel; 
using System.Windows.Forms; 

namespace Eagle_Eye_Class_Finder 
{ 
    /// <summary> 
    /// Summary description for Form2. 
    /// </summary> 
    public class YOURCLASSSCHEDULE : System.Windows.Forms.Form 
    { 
     public System.Windows.Forms.LinkLabel linkLabel1; 
     public System.Windows.Forms.LinkLabel linkLabel2; 
     public System.Windows.Forms.LinkLabel linkLabel3; 
     public System.Windows.Forms.LinkLabel linkLabel4; 
     private Button button1; 

     /// Required designer variable. 

     public System.ComponentModel.Container components = null; 

     public YOURCLASSSCHEDULE() 
     { 
      // 
      InitializeComponent(); 

      // TODO: Add any constructor code after InitializeComponent call 
     } 

     /// Clean up any resources being used. 
     protected override void Dispose(bool disposing) 
     { 
      if (disposing) 
      { 
       if (components != null) 
       { 
        components.Dispose(); 
       } 
      } 
      base.Dispose(disposing); 
     } 

     #region Windows Form Designer generated code 
     /// <summary> 
     /// Required method for Designer support - do not modify 
     /// the contents of this method with the code editor. 
     /// </summary> 
     private void InitializeComponent() 
     { 
      System.ComponentModel.ComponentResourceManager resources = new System.ComponentModel.ComponentResourceManager(typeof(YOURCLASSSCHEDULE)); 
      this.linkLabel1 = new System.Windows.Forms.LinkLabel(); 
      this.linkLabel2 = new System.Windows.Forms.LinkLabel(); 
      this.linkLabel3 = new System.Windows.Forms.LinkLabel(); 
      this.linkLabel4 = new System.Windows.Forms.LinkLabel(); 
      this.button1 = new System.Windows.Forms.Button(); 
      this.SuspendLayout(); 
      // 
      // linkLabel1 
      // 
      this.linkLabel1.BackColor = System.Drawing.SystemColors.ActiveCaption; 
      this.linkLabel1.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D; 
      this.linkLabel1.Font = new System.Drawing.Font("Times New Roman", 14.25F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0))); 
      this.linkLabel1.LinkArea = new System.Windows.Forms.LinkArea(0, 7); 
      this.linkLabel1.LinkBehavior = System.Windows.Forms.LinkBehavior.HoverUnderline; 
      this.linkLabel1.Location = new System.Drawing.Point(41, 123); 
      this.linkLabel1.Name = "linkLabel1"; 
      this.linkLabel1.Size = new System.Drawing.Size(288, 32); 
      this.linkLabel1.TabIndex = 1; 
      this.linkLabel1.TabStop = true; 
      this.linkLabel1.Text = "Class 1"; 
      this.linkLabel1.TextAlign = System.Drawing.ContentAlignment.MiddleCenter; 
      this.linkLabel1.LinkClicked += new System.Windows.Forms.LinkLabelLinkClickedEventHandler(this.linkLabel1_LinkClicked); 
      // 
      // linkLabel2 
      // 
      this.linkLabel2.BackColor = System.Drawing.SystemColors.ActiveCaption; 
      this.linkLabel2.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D; 
      this.linkLabel2.Font = new System.Drawing.Font("Times New Roman", 14.25F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0))); 
      this.linkLabel2.LinkBehavior = System.Windows.Forms.LinkBehavior.HoverUnderline; 
      this.linkLabel2.Location = new System.Drawing.Point(467, 123); 
      this.linkLabel2.Name = "linkLabel2"; 
      this.linkLabel2.Size = new System.Drawing.Size(288, 32); 
      this.linkLabel2.TabIndex = 2; 
      this.linkLabel2.TabStop = true; 
      this.linkLabel2.Text = "Class 2"; 
      this.linkLabel2.TextAlign = System.Drawing.ContentAlignment.MiddleCenter; 
      this.linkLabel2.VisitedLinkColor = System.Drawing.Color.Navy; 
      this.linkLabel2.LinkClicked += new System.Windows.Forms.LinkLabelLinkClickedEventHandler(this.linkLabel2_LinkClicked); 
      // 
      // linkLabel3 
      // 
      this.linkLabel3.BackColor = System.Drawing.SystemColors.ActiveCaption; 
      this.linkLabel3.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D; 
      this.linkLabel3.Font = new System.Drawing.Font("Times New Roman", 14.25F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0))); 
      this.linkLabel3.LinkBehavior = System.Windows.Forms.LinkBehavior.HoverUnderline; 
      this.linkLabel3.Location = new System.Drawing.Point(41, 311); 
      this.linkLabel3.Name = "linkLabel3"; 
      this.linkLabel3.Size = new System.Drawing.Size(288, 32); 
      this.linkLabel3.TabIndex = 3; 
      this.linkLabel3.TabStop = true; 
      this.linkLabel3.Text = "Class 3"; 
      this.linkLabel3.TextAlign = System.Drawing.ContentAlignment.MiddleCenter; 
      this.linkLabel3.LinkClicked += new System.Windows.Forms.LinkLabelLinkClickedEventHandler(this.linkLabel3_LinkClicked); 
      // 
      // linkLabel4 
      // 
      this.linkLabel4.BackColor = System.Drawing.SystemColors.ActiveCaption; 
      this.linkLabel4.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D; 
      this.linkLabel4.Font = new System.Drawing.Font("Times New Roman", 14.25F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0))); 
      this.linkLabel4.LinkBehavior = System.Windows.Forms.LinkBehavior.HoverUnderline; 
      this.linkLabel4.Location = new System.Drawing.Point(467, 311); 
      this.linkLabel4.Name = "linkLabel4"; 
      this.linkLabel4.Size = new System.Drawing.Size(288, 32); 
      this.linkLabel4.TabIndex = 4; 
      this.linkLabel4.TabStop = true; 
      this.linkLabel4.Text = "Class 4"; 
      this.linkLabel4.TextAlign = System.Drawing.ContentAlignment.MiddleCenter; 
      this.linkLabel4.LinkClicked += new System.Windows.Forms.LinkLabelLinkClickedEventHandler(this.linkLabel4_LinkClicked); 
      // 
      // button1 
      // 
      this.button1.BackColor = System.Drawing.SystemColors.ActiveCaptionText; 
      this.button1.FlatAppearance.BorderColor = System.Drawing.Color.FromArgb(((int)(((byte)(0)))), ((int)(((byte)(0)))), ((int)(((byte)(64))))); 
      this.button1.FlatStyle = System.Windows.Forms.FlatStyle.Popup; 
      this.button1.Font = new System.Drawing.Font("Pristina", 12F, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, ((byte)(0))); 
      this.button1.ForeColor = System.Drawing.SystemColors.ActiveCaption; 
      this.button1.ImageAlign = System.Drawing.ContentAlignment.TopCenter; 
      this.button1.Location = new System.Drawing.Point(358, 206); 
      this.button1.Name = "button1"; 
      this.button1.Size = new System.Drawing.Size(101, 25); 
      this.button1.TabIndex = 5; 
      this.button1.Text = "Go Back"; 
      this.button1.UseVisualStyleBackColor = false; 
      this.button1.Click += new System.EventHandler(this.button1_Click); 
      // 
      // YOURCLASSSCHEDULE 
      // 
      this.AutoScaleBaseSize = new System.Drawing.Size(6, 15); 
      this.BackgroundImage = ((System.Drawing.Image)(resources.GetObject("$this.BackgroundImage"))); 
      this.BackgroundImageLayout = System.Windows.Forms.ImageLayout.Stretch; 
      this.ClientSize = new System.Drawing.Size(790, 482); 
      this.Controls.Add(this.button1); 
      this.Controls.Add(this.linkLabel4); 
      this.Controls.Add(this.linkLabel3); 
      this.Controls.Add(this.linkLabel2); 
      this.Controls.Add(this.linkLabel1); 
      this.Font = new System.Drawing.Font("OldDreadfulNo7 BT", 8.25F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0))); 
      this.Name = "YOURCLASSSCHEDULE"; 
      this.Text = "Your Classes"; 
      this.Load += new System.EventHandler(this.Form2_Load); 
      this.ResumeLayout(false); 

     } 
     #endregion 

     public void Form2_Load(object sender, System.EventArgs e) 
     { 
      // if (text == "900456317") 
      // { 

      //} 

     } 

     public void linkLabel1_LinkClicked(object sender, System.Windows.Forms.LinkLabelLinkClickedEventArgs e) 
     { 

      System.Diagnostics.Process.Start("http://www.georgiasouthern.edu/map/"); 
     } 

     private void linkLabel2_LinkClicked(object sender, LinkLabelLinkClickedEventArgs e) 
     { 
      System.Diagnostics.Process.Start("http://www.georgiasouthern.edu/map/"); 
     } 

     private void linkLabel3_LinkClicked(object sender, LinkLabelLinkClickedEventArgs e) 
     { 
      System.Diagnostics.Process.Start("http://www.georgiasouthern.edu/map/"); 
     } 

     private void linkLabel4_LinkClicked(object sender, LinkLabelLinkClickedEventArgs e) 
     { 
      System.Diagnostics.Process.Start("http://www.georgiasouthern.edu/map/"); 
     } 

     private void button1_Click(object sender, EventArgs e) 
     { 
      Form1 form1 = new Form1(); 
      form1.Show(); 
      this.Hide(); 
     } 
    } 
} 

Answer 1

您正在创建2个不同的数组，一个在构造函数中，另一个在方法中。如果将 IDnumber[] IDnumbers = new IDnumber[3]; 行移动到方法的外部，并删除构造函数中的相同构造函数，它应该可以工作

Answer 2

编译完全与Exceptions无关。我会建议看看异常的堆栈跟踪，试图找到错误发生的地方，然后从那里开始。

看起来像GetSchedule.cs第24行是一个很好的开始！

Answer 3

的问题是在这if声明：

 IDnumber[] IDnumbers = new IDnumber[3]; 
     foreach (IDnumber IDCandidateMatch in IDnumbers) 
     { 

      if (IDCandidateMatch.ID == ID) 

你有三个元素创建数组，但所有元素都为空。当你遍历它们时，对IDCandidateMatch.ID的引用会生成NullReferenceException。