是否可以在C＃中将类型设置为超类uf的变量？

Question

More Informations:

EDIT: better sample:

I have a class in a Libary called UserAccount, its abstact. then i have some functionality like this in the library:

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;
    }
}

Cuz this is a independent library the UserAccount has not all Propertys i want to use:

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....
}

Then i want to do this:

ExtendedUserAccount newAccount = UserAccountService.CreateUserAccount(new UserAccount);

But this will not work. i now its not correct but i need something similar...

anyone has an idea??

Answer 1

That looks like a code smell and you probably need to redesign your types... But anyway, this should work:

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

This generic method takes an instance of a type that must extend UserAccount (or be an UserAccount itself), and declare a parameterless constructor. This last restriction will allow you to do this: TAccount account = new TAccount() .

Answer 2

I recommand the factory pattern

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