How to use a superclass method using reflections C#

Question

I have a bunch of classes that inherit from a single class. I'm using reflections to access the classes, since the ones that will be accessed will change in runtime.

But I am having some trouble when trying to invoke a method declared at superclass.

Here is my parent class:

public class ParentClass {

    public ParentClass (Type type) {

    }

    public string method0String () {
        return string;
    }

    public void method1Void (string) {

    }

}

Here is my child class:

public class ChildClass : ParentClass {

    public ParentClass () : base(typeof(ChildClass)) {

    }

}

Here is the abstract class code where I cast the methods:

Type childType = Type.GetType(className[i]);
ConstructorInfo childConstructor = childType.GetConstructor(new Type[0]);

object childObject = null;
childObject = childConstructor.Invoke(childObject, new object[0]);

MethodInfo parentMethod0String = childType.GetMethod("method0String");
MethodInfo parentMethod1Void = childType.GetMethod("method1Void");

parentMethod1Void.Invoke(childObject, new object[]{argString});
object finalString = parentMethod0String.Invoke(childObject, new object[0]);

The MethodInfos are always null, which causes this error when I try to invoke them:

System.NullReferenceException: Object reference not set to an instance of an object

I haven't found anyway around this.

Basically, I just need to invoke a super method using the child as the dynamic object. How can I achieve this?

@Edit

After @nvoigt answer, my code looks like this:

Type childType = Type.GetType(className[i]);
object childObject = Activator.CreateInstance(childType);

Type parentType = Type.GetType("ParentClass");
MethodInfo parentMethod0String = parentType.GetMethod("method0String");
MethodInfo parentMethod1Void = parentType.GetMethod("method1Void");

parentMethod1Void.Invoke(childObject, new object[]{argString});
object finalString = parentMethod0String.Invoke(childObject, new object[0]);

And the error is a little different:

System.Reflection.TargetException: Object does not match target type.

GetConstructor takes a array with the constructor parameters, not the target object instance — vc 74, Jul 16 '15 at 15:23
@vc74 Yeah, I know. But for some reason it was null after invoking the constructor. I now changed to Activator.CreateInstance( ) to avoid junky code. — Leonardo Gigliotti, Jul 16 '15 at 17:16
@eddie_cat the link above, with the answer being on using BindingFlags.FlattenHierarchy did not work for me. Sorry. — Leonardo Gigliotti, Jul 16 '15 at 17:16
did you checked the value of className[i]? Is it correct?I tested it by changing the className[i] to "ChildClass", and it works fine. — Taher Rahgooy, Jul 16 '15 at 17:48
@T.Rahgooy Sorry, the new error description was wrong. It says the type is not valid, not that there is no reference. — Leonardo Gigliotti, Jul 16 '15 at 17:57
replace the className[i] with "childClass" and check if it works or not — Taher Rahgooy, Jul 16 '15 at 18:03
It did... But the problem is... The list of which classes are going to pass through these methods is variable. I can't call it hardcoded like this. Is it because of the array? — Leonardo Gigliotti, Jul 16 '15 at 18:10
Actually, I will check manually all twenty classes and search for any that breaks the code. — Leonardo Gigliotti, Jul 16 '15 at 18:11
The problem arises when one of those classes is not a child of the base class. — Taher Rahgooy, Jul 16 '15 at 18:13
Oh boy... The problem is in the shell script that generates this classes! Thank you @T.Rahgooy! Sorry for the inconvenient. — Leonardo Gigliotti, Jul 16 '15 at 18:14

score 0 · Answer 1 · answered Jul 16 '15 at 15:29

0

You can do it this way:

namespace StackOverFlowTest
{
  using System;

  class BaseClass
  {
    public int BaseClassMethod(int x)
    {
      return x * x;
    }
  }

  class DerivedClass : BaseClass
  {
  }

  class Program
  {
    static void Main()
    {
      var derivedType = typeof(DerivedClass);
      var baseType = typeof(BaseClass);

      var method = baseType.GetMethod("BaseClassMethod");

      var derivedInstance = Activator.CreateInstance(derivedType);

      var result = method.Invoke(derivedInstance, new object[] { 42 });

      Console.WriteLine(result);
      Console.ReadLine();
    }
  }
}

answered Jul 16 '15 at 15:29

nvoigt

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Yeah, I could do it like that, but there are several classes since they are autogenerated from an external database... I would really need something more automated. :/ – Leonardo Gigliotti Jul 16 '15 at 15:32
What exactly do you need automated? You could easily automate this. – nvoigt Jul 16 '15 at 15:33
Sorry, I misread your answer. I actually tried your solution, but the problem is... System.Reflection.TargetException: Object does not match target type. – Leonardo Gigliotti Jul 16 '15 at 17:17
So what *do* you receive instead? What is your current code? – nvoigt Jul 16 '15 at 17:31

How to use a superclass method using reflections C#

1 Answers1