Call interface method using reference of class

Question

I want to call an interface method using the reference of a class which implements that interface. I am using reflection for that but my code is not working and I am getting null object reference exception. The code is give below:

interface IntA
{
    void MethodFirst();
}

interface IntB
{
    void MethodFirst();
}

class ClassA : IntA, IntB
{
    public void MethodFirst()
    {
        Console.WriteLine("this.ClassA.MethodFirst");
    }
    void IntA.MethodFirst()
    {
        Console.WriteLine("IntA.ClassA.MethodFirst");
    }
    void IntB.MethodFirst()
    {
        Console.WriteLine("IntB.ClassA.MethodFirst");
    }
}

class Program
{
    static void Main(string[] args)
    {            
        Type t = Type.GetType("ClassA");
            t.GetMethod("MethodFirst").Invoke(Activator.CreateInstance(t,null), null);

        Console.ReadLine();
    }        
}

Please let me know what I am doing wrong over here.

simply cast your class to interface and call your method. you don't need reflection — M.kazem Akhgary
– M.kazem Akhgary, Commented Dec 1, 2016 at 7:00
Thanks M. kazem Akhgary. It was an interview question to call it using reflection. — gliese 581 g
– gliese 581 g, Commented Dec 1, 2016 at 7:12
using reflection is something at expert level and you only use it when you really need it. that's very rare. if you are good programmer you never need reflection ;) — M.kazem Akhgary
– M.kazem Akhgary, Commented Dec 1, 2016 at 7:13

Nirman · Accepted Answer · 2016-12-01 07:23:58Z

1

You need to try creating instance of your class using the full namespace of that class. for example,

Type t = Type.GetType("ConsoleApplication1.ClassA");

In case, if you want to call a method from a particular interface -

Type t = Type.GetType("ConsoleApplication1.ClassA");
t.GetInterface("ConsoleApplication1.IntB").GetMethod("MethodFirst").Invoke(Activator.CreateInstance(t, null), null);

edited Dec 1, 2016 at 7:23

answered Dec 1, 2016 at 7:02

Nirman

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1 Comment

gliese 581 g Over a year ago

Thanks! It worked. But now I want to call IntB.MethodFirst. How can I call it?

Bob Dust · Accepted Answer · 2016-12-01 07:02:39Z

0

        IntA classA = new ClassA();
        classA.MethodFirst();
        Console.ReadLine();

answered Dec 1, 2016 at 7:02

Bob Dust

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