覆盖非泛型类的抽象泛型方法 [英] overriding abstract generic method from non generic class

问题描述

class Drawer
{
    public abstract void Draw<T>(T type);    
}

派生类#1

class ADrawer : Drawer
{
    public override void Draw<T>(List<T> list)
    {
        foreach (var a in list)
        {
            DrawA(a);
        }
    }

    public void DrawA(Agent a)
    {
        //draw code here
    }
}

派生类#2

class AnotherDrawer : Drawer
{
    public override void Draw<T>(T number)
    {
        if (number == 1)
        {
            //draw code
        }
    }
}

错误在 #1 派生类中:找不到合适的方法来覆盖"

The error is in the #1 derived class : "no suitable method found to override"

我应该在基类中使用虚拟"还是抽象"?

我应该如何设置基参数类型以允许派生类中的各种参数?

How should I set the base parameter type to allow a variety of parameters in derived classes?

推荐答案

您的代码有更多问题，而不仅仅是您询问的问题.暂时搁置覆盖问题，类 ADrawer 需要一个类型约束(where T : Agent):

Your code has more problems than just the one you ask about. Setting aside the override question for the moment, class ADrawer needs a type constraint (where T : Agent):

class ADrawer : Drawer 
{ 
    public void Draw<T>(List<T> list) where T : Agent
    { 
        foreach (var a in list) 
        { 
            DrawA(a); 
        } 
    }
    public void DrawA(Agent a) 
    { 
        //draw code here 
    } 
} 

如果没有这个约束，将 a 传递给 DrawA 是不合法的，因为 a 是 T，没有约束就没有从 T 类型到 Agent 类型的隐式转换.

Without that constraint, it's not legal to pass a to DrawA, because a is a reference of type T, and without the constraint there is no implicit conversion from type T to type Agent.

AnotherDrawer 类非法使用了 == 运算符.不能将 == 运算符应用于 T 和 int 类型的操作数.您可以通过使用 object.Equals 覆盖来解决这个问题.

The AnotherDrawer class has an illegal use of the == operator. It's not possible to apply the == operator to operands of type T and int. You could get around that by using the object.Equals override.

最后，基类有错误，因为它是一个包含抽象成员的非抽象类.

Finally, the base class has an error because it is a non-abstract class containing an abstract member.

然而，一般来说，这段代码表明类应该是通用的，而不是方法:

In general, however, this code indicates that the class should be generic, rather than the method:

abstract class Drawer<T>
{
    public abstract void Draw(T type);
}

派生类#1

class ADrawer : Drawer<List<Agent>>
{
    public override void Draw(List<Agent> list)
    {
        foreach (var a in list)
        {
            DrawA(a);
        }
    }       

    public void DrawA(Agent a)
    {
        //draw code here
    }
}

派生类#2

class AnotherDrawer : Drawer<int>
{
    public override void Draw(int number)
    {
        if (number == 1)
        {
            //draw code
        }
    }
}

要跟进 Eric Lippert 的评论，这也是我对您的问题的第一反应，您可以考虑改为使用此设计:

To follow up on Eric Lippert's comment, which was also my first reaction to your question, you might consider this design instead:

abstract class Drawer<T>
{
    public abstract void Draw(T type);
    public void DrawMany(IEnumerable<T> types)
    {
        foreach (var t in types)
            Draw(t);
    }
}

派生类#1

class ADrawer : Drawer<Agent>
{
    public override void DrawA(Agent a)
    {
        //draw code here
    }
}

派生类 #2 没有改变.

Derived class #2 is unchanged.

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