从不同的C＃类访问列表对象

Question

I am trying to workout to see how I can access list items from a different class and to update the same, I have my code below for clarification.

class list
{
    private List<Person> people;
    public List<Person> People
    {
       get { return people; }
       set { people = value; }
    }
}

public partial class Form2 : Form
{
    Person p = new Person();
    list l = new list();

    p.Name = textBox1.Text;
    p.Streetaddress = textBox2.Text;
    p.Email = textBox3.Text;
    p.Birthday = dateTimePicker1.Value;
    p.AdditionalNotes = textBox4.Text;

    l.People.Add(p);
    listView2.Items.Add(p.Name);
}

there is Person class which has instance variables Name, Streetaddress etc.

Getting an error

Nullreference exception was unhandled

Please help me..

Answer 1

You need to instantiate the inner List<Person> when the List class is instantiated. Otherwise it will be null.

class list
{

   private List<Person> people = new List<Person>();
   public List<Person> People
   {
       get { return people; }
       set { people = value;}
   }

}

Answer 2

Basically, you have defined a property People in class list but have not initialized it. Just initialize it in the constructor of list class.

Can you try:

class list
    {

       private List<Person> people;
       public List<Person> People
       {
           get { return people; }
           private set { people = value;}
       }

       public list()
       {
         people = new List<Person>();
       }
    }