Question

有人能说出这里有什么问题吗？

public class Student 
{
    public List<Class> Classes { get; set; }

    public Student(List<Class> classes)
    {
       this.Classes = classes;
    }
    public Student(Class class) 
    {
        //This does not work
        //Error: Object reference not set to an instance of an object.
        this.Classes.Add(class);
    }
}

将其称为以下作品

var classes = new List<Classes>();
classes.Add(new Class("English", "Elective"));
classes.Add(new Class("Math", "Core"));
..more classes to add
Student student = new Student(classes);

当我这样打电话时（只需要添加一个课程）

Student student = new Student(new Class("Masters","Accounts"));

我收到错误。谢谢。

Answer 1

Class的重载需要在添加类之前初始化类。试试这个：

public class Student 
{
    public List<Class> Classes { get; set; }

    public Student(List<Class> classes)
    {
       this.Classes = classes;
    }
    public Student(Class class) 
    {
        this.Classes = new List<Class>();
        this.Classes.Add(class);
    }
}

Answer 2

在第二个构造函数中，您从未初始化Classes

Answer 3

this.Classes未初始化：

public class Student 
{
    public List<Class> Classes { get; set; }

    public Student(List<Class> classes)
    {
       this.Classes = classes;
    }
    public Student(Class class) 
    {
        this.Classes = new List<Class>();
        this.Classes.Add(class);
    }
}

Answer 4

在尝试向其添加对象之前，您需要初始化Classes。

构造函数重载

4 个答案: