带有列表的 C# 泛型

Question

I have these multiple versions of these two classes:

public class Contests : List<Contest> { }

public class Contest {

    // stuff specific to Contest;       

    public Contests parent;

    public void Attach() {
        parent.Add(this);
    }
}

And here's another:

public class Transactions : List<Transaction> { }

public class Transaction {

    // stuff specific to Transaction;       

    public Transactions parent;

    public void Attach() {
        parent.Add(this);
    }
}

So that I don't repeat code, can I take out the Attach into a base class using generics?

public class MBData<T> {

    public T parent;

    public void Attach() {
        T.Add(this);
    }
}

I tried with the following but I receive an error about not being able to convert between Contests and MBDatas<MBData<Contests>> .

public class MBDatas<S> : List<S> { }

public class MBData<B> where B : MBDatas<MBData<B>> { }

public class Contests : MBDatas<Contest> { }

public class Contest : MBData<Contests> { }

Answer 1

Does this work for you?

public abstract class MBData<P, C>
    where P : MBDatas<P, C>
    where C : MBData<P, C>
{
    public void Attach()
    {
        this.Parent.Add((C)(object)this);
    }
    public P Parent { get; set; }
}

public abstract class MBDatas<P, C> : List<C>
    where P : MBDatas<P, C>
    where C : MBData<P, C>
{ }

You are forced to do a nasty double cast (C)(object)this to get the Attach method to work and this is the only rub with this approach. It works, but you need to be careful that you define the child classes properly.

You can define your classes like this:

public class Contests : MBDatas<Contests, Contest> { }
public class Contest : MBData<Contests, Contest> { }
public class Transactions : MBDatas<Transactions, Transaction> { }
public class Transaction : MBData<Transactions, Transaction> { }

And finally, use them like this:

var cs = new Contests();
var c1 = new Contest() { Parent = cs };
var c2 = new Contest() { Parent = cs };

cs.Add(c1);
cs.Add(c2);

var ts = new Transactions();
var t1 = new Transaction() { Parent = ts };
var t2 = new Transaction() { Parent = ts };

ts.Add(t1);
ts.Add(t2);