C＃list.add（）的位置覆蓋對象0

Question

我更新我的問題這個 我創建新類學生

class Student 
    { 

     private string _firstName; 
     private string _lastName; 
     private int _exam1; 
     private int _exam2; 
     private int _exam3; 
     private int _finalExam; 


     // First Name Property 
     public string FirstName 
     { 
      get { return _firstName; } 
      set { _firstName = value; } 
     } 

     //Last Name Property 
     public string LastName 
     { 
      get { return _lastName; } 
      set { _lastName = value; } 
     } 

     //Exam 1 Property 
     public int Exam1 
     { 
      get { return _exam1; } 
      set { _exam1 = value; } 
     } 

     // Exam 2 Property 
     public int Exam2 
     { 
      get { return _exam2; } 
      set { _exam2 = value; } 
     } 

     //Exam 3 Property 
     public int Exam3 
     { 
      get { return _exam3; } 
      set { _exam3 = value; } 
     } 

     //Final Exam Property 
     public int FinalExam 
     { 
      get { return _finalExam; } 
      set { _finalExam = value; } 
     } 
    } 
} 

這是一個方法，我添加新的學生窗體類添加新的學生

public class AddStudent : Form 
    { 

     StudentForm stu = null; 

     public AddStudent() 
     { 
      InitializeComponent(); 
      stu = new StudentForm(); 
      stu.Show(); 

     } 

     private void btnSubmit_Click(object sender, EventArgs e) 
     { 
      // split the name into first and last name 
      string[] name = txtName.Text.Split(','); 
      Student std = new Student(); 
      std.FirstName = name[0]; 
      std.LastName = name[1]; 
      std.Exam1 = Int32.Parse(txtExam1.Text); 
      std.Exam2 = Int32.Parse(txtExam2.Text); 
      std.Exam3 = Int32.Parse(txtExam3.Text); 
      std.FinalExam = Int32.Parse(txtFinal.Text); 
      stu.addItem(std); 
      this.Hide(); 
     } 
    } 
} 

，這是它具有列表框中顯示的學生名單我的主要形式

public class StudentForm : Form 
    {    
     public StudentForm() 
     { 
      InitializeComponent(); 
     } 

     public List<Student> students = new List<Student>(); 

     public void addItem(Student std) 
     { 

      students.Add(std); 
      // it always show me 1 item in list 
      MessageBox.Show(students.Count.ToString()); 

     } 
} 

Answer 1

這是因爲你每次使用該行創建Student形式：

Student std = new Student(); 

所以每次你點擊提交按鈕時，您正在創建這將創建一個新的空public List<Student>

一種新形式的學生你需要從UI（StudentForm）和（AddStudentForm）獨立模型（Student）：

public class Student 
{ 
    public string FirstName { set; get; } 
    private string LastName { set; get; } 
    private int Exam1 { set; get; } 
    private int Exam2 { set; get; } 
    private int Exam3 { set; get; } 
    private int FinalExam { set; get; } 
} 

你並不需要創建一個新的StudentFormê當你添加一個Student。相反，在導航到添加屏幕時，您可以有一個StudentForm並使用ShowDialog()，這可以返回到StudentForm的相同實例。

Answer 2

是的，每當您創建Student表格的新實例並調用addItem()方法時，都會導致您的btnSubmit_Click錯誤。

你，而這個字段移動到一個單獨的類象

public class Data 
{ 
    private string _firstName; 
    private string _lastName; 
    private int _exam1; 
    private int _exam2; 
    private int _exam3; 
    private int _finalExam; 
} 

必須在創建的窗體實例啓動像

public partial class AddStudent : Form 
    { 

Student stu = null; 
public AddStudent() 
{ 
    InitializeComponent(); 
    stu = new Student(); 
    stu.Show(); 
} 

變化Form1中

public List<Data> students = new List<Data>(); 

列表在按鈕點擊只需添加Data實例，如

private void btnSubmit_Click(object sender, EventArgs e) 
    { 
     // split the name into first and last name 
     string[] name = txtName.Text.Split(','); 
     Data std = new Data(); 
     std.FirstName = name[0]; 
     std.LastName = name[1]; 
     std.Exam1 = Int32.Parse(txtExam1.Text); 
     std.Exam2= Int32.Parse(txtExam2.Text); 
     std.Exam3 = Int32.Parse(txtExam3.Text); 
     std.FinalExam = Int32.Parse(txtFinal.Text); 
     stu.addItem(std); 
     this.Hide(); 
    } 

Answer 3

這裏是你的代碼是如何進展，與添加註釋和代碼無關去除：

private void btnSubmit_Click(object sender, EventArgs e) 
{ 
    ... 
    // create a _new_ Student form 
    Student std = new Student(); 

    ... 

    // Add the student form to itself (huh?) 
    std.addItem(std); 

    // hide this form 
    this.Hide(); 

    // show the new form 
    std.Show(); 
} 

所以，你總是顯示一個項目的新形式 - 這是剛剛創建的。

Answer 4

嘗試取出Class Student實例化出了大事 - btnSubmit_Click event Student std = new Student();