C＃阵列 - “对象引用不设置到对象的实例”

Question

我有一个主要的问题使这项工作。我需要做的就是让我的数组显示。

namespace OOP_3 
{ 
    public partial class Add_Child : Form 
    { 
     public Add_Child() 
     { 
      InitializeComponent(); 
     } 

     private void btnAddChild_Click(object sender, EventArgs e) 
     { 
      Mother m = new Mother(); 
      m.MyChildren = new Child[3]; 

      int ID = int.Parse(txtID.Text); 
      string FNAME = txtFname.Text; 
      string LName = txtLname.Text; 
      DateTime DOB = DateTime.Parse(txtDob.Text); 
      //Add children 

      label5.Text = m.GetMyChildrenDetails(); 
      if (addtoarray(m,ID,FNAME,LName,DOB) == true) 
      { 
       MessageBox.Show("added", "Add Child"); 
      } 
      else 
      { 
       MessageBox.Show("cannot add", "Child add - full"); 
      } 
     } 

     public bool addtoarray(Mother m, int ID, string FNAME, string LName,DateTime DOB) 
     { 
      for (int i = 0; i < m.MyChildren.Length; i++) 
      { 
       if (m.MyChildren[i]== null) 
       { 
        m.MyChildren[i] = new Child(m); //See comment below 
        m.MyChildren[i].ChildId = ID; 
        m.MyChildren[i].FirstName = FNAME; 
        m.MyChildren[i].LastName = LName; 
        m.MyChildren[i].DateOfBirth = DOB; 
        return true; 
       } 
      } 
      return false; 
     } 
    } 
} 

从代码注释：此行会破坏堆一切，重建阵列造成我有值，不会在我label5.text香港专业教育学院出现在琢磨研究了好几个小时，我认为IAM要么会疯了还是我的编码，该编码IAM :)请一些帮助将是不错只是noobie：）...... 如果需要的话，我会后我的课的和主要形式了:)

public class Mother 
{ 
    //Fields 
    private int motherId; 
    private string firstName; 
    private string lastName; 
    private string mobile; 
    private Child[] myChildren; //mother "has a" many children 

    //props 
    public Child[] MyChildren 
    { 
     get { return myChildren; } 
     set { myChildren = value; } 
    } 

    public string Mobile 
    { 
     get { return mobile; } 
     set { mobile = value; } 
    } 

    public string LastName 
    { 
     get { return lastName; } 
     set { lastName = value; } 
    } 

    public string FirstName 
    { 
     get { return firstName; } 
     set { firstName = value; } 
    } 

    public int MotherId 
    { 
     get { return motherId; } 
     set { motherId = value; } 
    } 

    //constructors 

    //methods 
    //Get Mother Details 
    public override string ToString() 
    { 
     return motherId + ", " + firstName + ", " + lastName + ", " + mobile; 
    } 

    //AddChild 
    public bool AddChild(Child myChild) 
    { 
     for (int i = 0; i < myChildren.Length; i++) 
     { 
      if (myChildren[i] != null) 
      { 
       myChildren[i] = myChild; 
       return true; 
      } 
     } 

     return false; 
    } 

    //GetMyChildrenDetails 
    public string GetMyChildrenDetails() 
    { 
     string msg = ""; 
     for (int i = 0; i < myChildren.Length; i++) 
     { 
      if (myChildren[i] != null) 
      { 
       msg += "\n" + myChildren[i]; 
      } 
     } 
     return msg; 
    } 

public class Child 
{ 
    //fields 
    private int childId; 
    private string firstName; 
    private string lastName; 
    private DateTime dateOfBirth; 
    private Mother myMother; //child "has a" mother 

    //props 
    public Mother MyMother 
    { 
     get { return myMother; } 
     set { myMother = value; } 
    } 

    public DateTime DateOfBirth 
    { 
     get { return dateOfBirth; } 
     set { dateOfBirth = value; } 
    } 

    public string LastName 
    { 
     get { return lastName; } 
     set { lastName = value; } 
    } 

    public string FirstName 
    { 
     get { return firstName; } 
     set { firstName = value; } 
    } 

    public int ChildId 
    { 
     get { return childId; } 
     set { childId = value; } 
    } 

    //constructors 
    //Child cannot be created without a mother 
    public Child(Mother myMother) 
    { 
     this.myMother = myMother; 
    } 
    //Child cannot be created without a mother 
    public Child(Mother myMother, int childId) 
    { 
     this.myMother = myMother; 
     this.childId = childId; 
    } 

    //methods 
    //Get Child Details 
    public override string ToString() 
    { 
     return childId + ", " + firstName + ", " + lastName + ", " + dateOfBirth; 
    } 

public partial class Form1 : Form 
{ 
    public Form1() 
    { 
     InitializeComponent(); 
    } 

    private void btnRegister_Click(object sender, EventArgs e) 
    { 

    } 

    private void menuStrip1_ItemClicked(object sender, ToolStripItemClickedEventArgs e) 
    { 

    } 

    private void closeToolStripMenuItem_Click(object sender, EventArgs e) 
    { 
     Close(); 
    } 

    private void BtnAddChild_Click(object sender, EventArgs e) 
    { 
     Add_Child child = new Add_Child(); 
     child.Show(); 
    } 

    private void btnRegister_Click_1(object sender, EventArgs e) 
    { 
     //create a mother object 
     Mother m = new Mother(); 
     m.MotherId = int.Parse(txtID.Text); 
     m.FirstName = txtFname.Text; 
     m.LastName = txtLname.Text; 
     m.Mobile = txtMobile.Text; 

Answer 1

给新孩子引用其父对象不是问题的原因。总之，你的状态：

“有值，不会在我label5.text显示”

这表明它要么是你的绑定有一个问题，你有没有实施INotifyPropertyChanged，或者你的UI更新机制不起作用（如果你不使用绑定）。正如你没有说明你用什么为UI，这是尽可能多的我可以帮助......

Answer 2

我的建议，你可以使用List而不是阵列，因为不是所有的母亲都有三个孩子。示例代码：

public static class Program 
{ 
    static void Main(string[] args) 
    { 
     Mother mother = new Mother { 
      FirstName = "M First", LastName = "M Last", Contact = "225632655" 
     }; 

     //Add dependents 
     mother.AddChild(new Child{ChildID = 1, FirstName = "Child FirstName 1", LastName = "Child LastName 1"}); 
     mother.AddChild(new Child{ChildID = 2, FirstName = "Child FirstName 2", LastName = "Child LastName 2"}); 
     mother.AddChild(new Child{ChildID = 3, FirstName = "Child FirstName 3", LastName = "Child LastName 3"}); 

     Console.WriteLine(mother); 
     //List all the mother dependents 
     foreach(Child c in mother.Children) 
     { 
      Console.WriteLine(c); 
     } 
     Console.ReadKey(); 
    } 
} 

class Mother 
{ 
    public string FirstName {get; set;} 
    public string LastName {get; set;} 
    public string Contact {get; set;} 
    private List<Child> _child; 
    public Mother() 
    { 
     _child = new List<Child>(); 
    } 

    public void AddChild(Child child) 
    { 
     _child.Add(child); 
    } 

    public List<Child> Children 
    { 
     get { return _child; } 
    } 

    public override string ToString() 
    { 
     return string.Format("{0}, {1} ({2})", LastName, FirstName, Contact); 
    } 
} 

class Child 
{ 
    public string FirstName {get; set;} 
    public string LastName {get; set;} 
    public int ChildID {get; set;} 

    public override string ToString() 
    { 
     return string.Format("{0} {1}, {2}", ChildID, LastName, FirstName); 
    } 
} 

我希望这会有所帮助。