调用基类静态方法时获取Caller派生类

Question

I was wondering if it's possible (even via reflection et similia) to get the caller derived-class inside of a called base-class static method.

For example, I've a base-class with a static method defined:

public MyBaseClass {
    public static void MyBaseClassStaticMethod() { /** ... **/ }
}

and a derived-from-it class:

public MyDerivedClass : MyBaseClass { }

then I call:

MyDerivedClass.MyBaseClassStaticMethod()

Is it possibile, inside of method MyBaseClassStaticMethod , to know which is the caller derived type ?
(ie MyDerivedClass )

I just need a string...

Answer 1

Generics in following way can be used to solve your scenario

public class BaseClass<TDerived> where TDerived : BaseClass<TDerived>
{
    public static void LogCallerType()
    {
        Console.WriteLine(typeof(TDerived).Name);
    }
}

public class FooClass : BaseClass<FooClass> { }

public class BooClass : BaseClass<BooClass> { }

class Program
{
    static void Main(string[] args)
    {
        FooClass.LogCallerType();
        BooClass.LogCallerType();
    }
}

This will in turn output the following

1. FooClass
2. BooClass

Answer 2

No, this is not possible - by no means. static methods are not polymorphal and as such this information simply doesn't exist.
Consider redesigning your code.

Update:

Upon compilation, the compiler replaces MyDerivedClass with the class the static method is actually declared on, in your case MyBaseClass .
So even in the IL you don't see MyDerivedClass . The information exists only in your source code. It doesn't exist in your compiled assembly.

Answer 3

A static method is statically bound to a certain class and does not really participate in the inheritance-chain. Thus it does not exist in the derived class. The static method therefor does not know that it was actually used in the derived class.

You can however - through a compiler-trick - access the static member from your derived class. As of this post on MSDN-forum a static member-access from a derived class is translated to a call from the base-class containing the static member. So MyDerivedClass.MyBaseClassStaticMethod is translated to MyBaseClass.MyBaseClassStaticMethod . Thus MethodBase.GetCurrentMethod().DeclaringType will allways return MyBaseClass .

So in short: no, it´s not possible to get the derived type from a static member.

Answer 4

First of all, the static method will not have access to the instance that is calling it. A static method is different from a normal class method in that it does not have access the 'this' reference to a class instance.

If you passed 'this' as a parameter to the static method, then you can try casting it as follows. Assume you have a number of derived class which you want to test for.

public static void MyBaseClassStaticMethod(MyBaseClass callingInstance)
{
    MyDerivedClass myDerivedClass = callingInstance as MyDerivedClass;
    MyDerivedClass2 myDerivedClass2 = callingInstance as MyDerivedClass2;
    MyDerivedClass3 myDerivedClass3 = callingInstance as MyDefivedClass3;
    ...

    // test for which derived class is calling
    if (myDerivedClass != null)
        ...
    else if (myDerivedClass2 != null)
        ...

    ...
}