c# - 是否可以设置一个类型为 C# 中类的超类的变量？

Question

更多信息：

编辑：更好的样本：

我在一个名为 UserAccount 的库中有一个类，它是抽象的。然后我在库中有一些这样的功能：

class UserAccountService
{
    public static UserAccount CreateUserAccount(String username, String password, String email)
    {
    UserAccount account = new UserAccount();
    account.Username = username;
    account.HashedPass = //Some crypting stuff with password
    account.Email = email;

    UserAccountRepository db = new UserAccountRepository();
    db.UserAccounts.Add(account);

    return account;
    }
}

因为这是一个独立的库，UserAccount 没有我想使用的所有属性：

class ExtendedUserAccount : UserAccount
{
// define some additional methods and propertys
public Contact Contacts{get;set}// this property is only used in one application where i use the Library....
}

然后我想这样做：

ExtendedUserAccount newAccount = UserAccountService.CreateUserAccount(new UserAccount);

但这行不通。我现在不正确，但我需要类似的东西......

有人有想法吗？

Answer 1

这看起来像代码味道，你可能需要重新设计你的类型......但无论如何，这应该工作：

class UserAccountService
{
    public static TAccount CreateUserAccount<TAccount>(TAccount account)
          where TAccount : UserAccount, new()
    {
        //create new useraccount...
        return account;
    }
}

这个泛型方法接受一个必须扩展 UserAccount（或者是 UserAccount 本身）的类型的实例，并声明一个无参数的构造函数。最后一个限制将允许您这样做：TAccount account = new TAccount().

Answer 2

我推荐工厂模式

class UserAccountService
{
    // ctor with interfaces
    public IUserAccount CreateUserAccount()
    {
        // create instance
        return result;
    } 

    // ctor with generic
    public IUserAccount CreateUserAccount<T>() where T : UserAccount
    {
        var account = Activator.CreateInstance<T>();
        return account;
    } 
}

class ExtendedUserAccount : UserAccount
{
    // define some additional methods and propertys
}

class UserAccount : IUserAccount
{

}

internal interface IUserAccount
{
}

Answer 3

Just to make it clear

Are this you conditions?

• UserAccountService & UserAccount are in Library A
• ExtendedUserAccount is, and only will be in Library B
• you can't/dont't want to edit library A

then the answer can be: Make 1 entry point in Library B that make this possible