c# - 在类中创建方法来更新类中保存的列表

Question

我正在尝试在名为“顾问”的类中创建一个列表，其中包含由 1 个顾问实例提供建议的学生列表。我创建了一个学生类(class)，并且没有遇到任何问题，但是我在运行时在我的顾问类(class)中遇到错误。

class Advisers
{
    private string _Fname;
    private string _Lname;
    private string _Department;
    private List<Student> _StudentsAdvised;   

    //constructor
    public Advisers()
    {
        _Fname = "";
        _Lname = "";
        _Department = "";
        _StudentsAdvised = null;
    }

    public void AddToList(Student newStudent)
    {
        _StudentsAdvised.Add(newStudent);
    }

    public List<Student> StudentsAdvised
    {
        get { return _StudentsAdvised; }
        set { _StudentsAdvised = value; }
    }

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

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

    public string Department
    {
        get { return _Department; }
        set { _Department = value; }
    }       
}

我在主窗体中调用 AddToList 方法，将学生的实例添加到 Adviser 类中保存的 StudentsAdvised 列表中。

private void stuAssignAdviBtn_Click(object sender, EventArgs e)
    {
        int stuIndex = stuLstbox.SelectedIndex;
        int advIndex = adviListBox.SelectedIndex;

        if (stuLstbox.SelectedIndex != -1 && adviListBox.SelectedIndex != -1)
        {
            string AdvLastName = AdviserList[advIndex].LastName;
            StudentList[stuIndex].AdviserLastName = AdvLastName;


            AdviserList[advIndex].AddToList(StudentList[stuIndex]);
        }
        else
        {
            MessageBox.Show("Select 1 student and 1 adviser.");
        }
    }

错误消息出现在此处的 Adviser 类中:

public void AddToList(Student newStudent)
{
    _StudentsAdvised.Add(newStudent);
}

我该怎么做？

Answer 1

我没有看到你初始化你的 List<Student> _StudentsAdvised任何地方

你可以在类构造函数中做到这一点

//constructor
public Advisers()
{
    _Fname = "";
    _Lname = "";
    _Department = "";
    _StudentsAdvised = new List<Student>();
}