Question

头等舱

 class Tasks
{
    public List<Ck> listCk { get; set; }
}

第二类

class Ck
{
    public string CkName { get; set; }
    public string CkConentent { get; set; }
}

现在我想将Ck添加到Tasks.listCk

Tasks t = new Tasks();
Ck ck = new Ck();
ck.CkName = "s1";
ck.CkConentent = "s2";

t.listCk.Add(ck); //Here I get NullReferenceException

System.NullReferenceException：“对象引用未设置为对象的实例。” MojDevnik.Tasks.listaCk.get返回null。

Answer 1

您需要初始化列表，可以在构造函数中或在为其赋值之前进行初始化。下面是一个如何在构造函数中执行此操作的示例。

class Tasks
{
    public List<Ck> listCk { get; set; }

    public Task() {
        listCk = new List<Ck>();
    }

}

Answer 2

您需要首先实例化列表

更改此

 class Tasks
{
    public List<Ck> listCk { get; set; }
}

到

 class Tasks
{
    public List<Ck> listCk { get; set; } = new List<Ck>();
}

或

Tasks t = new Tasks();
                Ck ck = new Ck();
                ck.CkName = "s1";
                ck.CkConentent = "s2";

                t.listCk.Add(ck); *Here i get NullReferenceException*

到

Tasks t = new Tasks();
                Ck ck = new Ck(){listCk  = new List<Ck>()};
                ck.CkName = "s1";
                ck.CkConentent = "s2";

                t.listCk.Add(ck); *Here i get NullReferenceException*

或

添加一个构造函数

   class Tasks
{
    public List<Ck> listCk { get; set; }

    public Task() {
        listCk = new List<Ck>();
    }

}

将类添加到另一个类属性public List <class> ListOfThatClass {get;组; }

2 个答案: