在asp.net中位于另一个对象中的对象数组中插入对象

现在，我正在创建对象

public class User

{

private string name;
private string addressLine1;
private string addressLine2;
private string city;
private string zip;
private string state;
private string emailAddress;
private string password;
private string loginpassword;
private SoldBook[] soldBooks;

public string Name
{
    get { return name; }
    set { name = value; }
}
public string AddressLine1
{
    get { return addressLine1; }
    set { addressLine1 = value; }
}
public string AddressLine2
{
    get { return addressLine2; }
    set { addressLine2 = value; }
}
public string City
{
    get { return city; }
    set { city = value; }
}
public string Zip
{
    get { return zip; }
    set { zip = value; }
}
public string State
{
    get { return state; }
    set { state = value; }
}
public string EmailAddress
{
    get { return emailAddress; }
    set { emailAddress = value; }
}
public string Password
{
    get { return password; }
    set { password = value; }
}
public string LoginPassword
{
    get { return loginpassword; }
    set { loginpassword = value; }
}
public SoldBook[] SoldBooks
{
    get { return soldBooks; }
    set { soldBooks = value; }
}
}



public class SoldBook


{



public string ISBNNumber
{
    get { return isbnnumber; }
    set { isbnnumber = value; }
}
public string Title
{
    get { return title; }
    set { title = value; }
}
}

现在我想在用户对象中的SoldBook数组中添加sell对象。 我正在尝试做user1.SoldBooks.addsell； 但这是不对的。在用户对象的数组SoldBook中添加已售出对象的正确方法是什么

user user1 = new User; 


SoldBook sold = new SoldBook();
sold.ISBNNumber ="value";
sold.Title = "value";

public class User
{   
private List<SoldBook> soldBooks;
public List<SoldBook> SoldBooks
{
   get { return soldBooks; }
   set { soldBooks = value; }
}

user user1 = new User; 
SoldBook sold = new SoldBook();
sold.ISBNNumber ="value";
sold.Title = "value";

user1.SoldBooks.add(sold);