Question

我有以下代码可以在Base类的对象下执行操作：

class Program
{
    static void Main(string[] args)
    {
        var list = new List<Base>() { new A(), new B() };
        var v = new Visitor();
        list.ForEach(e => e.Accept(v));
    }
}

public abstract class Base
{
    public abstract void Accept(Visitor visitor);
}

public class A : Base
{
    public override void Accept(Visitor visitor) => visitor.Visit(this);
}

public class B : Base
{
    public override void Accept(Visitor visitor) => visitor.Visit(this);
}

public class Visitor
{
    Writer writer = new Writer();
    public void Visit(A a) => writer.Write(a);
    public void Visit(B b) => writer.Write(b);
}

public class Writer
{
    public void Write(A a) => Console.WriteLine("A");
    public void Write(B b) => Console.WriteLine("B");
}

我想将Writer划分为单独的类，因为将会有许多其他具有复杂层次结构的实体。可能是：

public interface Writer<T> where T : Base
{
    void Write(T t);
}

public class WriterA : Writer<A>
{
    public void Write(A t) => Console.WriteLine("A");
}

public class WriterB : Writer<B>
{
    public void Write(B t) => Console.WriteLine("B");
}

但是我不知道如何通过给定的type参数实例化适当的类，而不是显式调用它们。谢谢。

Answer 1

您将需要写WriterFactory：

class WriterFactory{
    Dictionary<string, Func<object>> _creators = { 
            { "A", ()=> new WriterA() },
            { "B", ()=> new WriterB() } 
       };

    public Writer<T> Create<T>(){
         return (Writer<T>)_creators[typeof(T).Name]();
    }

比起您可以在Visitor中使用它而言：

public class Visitor
{
    Writer writerFactory = new WriterFactory();
    public void Visit(A a) => writerFactory.Create<A>().Write(a);
    public void Visit(B b) => writerFactory.Create<B>().Write(b);
}

在C＃中通过类型参数实例化适当的泛型类

1 个答案: