C#继承-保存对最后一个实例的引用 [英] C# inheritance - save reference to last instance

问题描述

我只是提出了一个非常奇怪的问题，我无法弄清楚如何解决它.

I just came up with a really odd problem and I wasn't able to figure out how to solve it.

我有3个班级，班级A是班级B和班级C的基础，即:

I have 3 classes, the class A is the base for B and C, that is:

class A { ... }
class B : A { ... }
class C : B { ... }

现在，我想在这些类中具有一个静态属性，用于存储创建的每个类的最后一个对象，例如:

Now I would like to have a static property in these classes that stores the last object of each classes created, for example:

class A
{
    static public A lastInstance;
}

class B : A
{
    public B()
    {
        lastInstance = this;
    }
}

class C : A
{
    public C()
    {
        lastInstance = this;
    }
}

我想要实现的是能够为每个子类检索一个实例，例如:

What I would like to achieve is to be able to retrieve an instance for each subclass, for example:

var v1 = new B();
var v2 = new C();

var v3 = B.lastInstance;    // v3 == v1 and v3 != v2
var v4 = C.lastInstance;    // v4 == v2 and v4 != v3

有可能吗?

The only approach that seems promising to me shown in C# Static instance members for each inherited class: is it really the only chance I have to avoid defining a static member manually for each class?

推荐答案

我认为可以使用Dictionary完成，这是我现在唯一想到的方法:

I think this could be done with Dictionary and that's the only way i can think of right now:

class A {
    static Dictionary<Type, A> _LastInstances = new Dictionary<Type, A>(); // because every subclass will inherit from A
    public static A LastInstance {
        get {
            if ( _LastInstances.ContainsKey(GetType()) ) {
                return _LastInstances[GetType()];
            }
            return null;
        }

        protected set {
            if ( _LastInstances.ContainsKey(GetType()) ) {
                _LastInstances[GetType()] = value;
            } else {
                _LastInstances.Add(GetType(), value);
            }
        }
}

class B : A {
    public B(){
        LastInstance = this;
    }
}

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