Using delegates with non static methods in C#

Question

Asking the same question as Using delegates with non static methods [no picked answer] so as to bring a closure to it.

So I use @Adam Marshall's solution, it works, but as soon as I start using it, i.e., Testit():

using System;

public class TestClass
{
    private delegate void TestDelegate();
    TestDelegate testDelegate;

    public TestClass()
    {
        testDelegate = new TestDelegate(MyMethod);
    }

    public static void Testit()
    {
        testDelegate();
    }

    private virtual void MyMethod()
    {
        Console.WriteLine("Foobar");
    }
}

public class Program
{
    public static void Main()
    {
        Console.WriteLine("Hello World");
        TestClass.Testit();
    }
}

It started to give the followig Error:

A object reference is required for the non-static field, method, or property

You can test it out here . How to fix it? (Please fix it if possible instead of directing me to other posts, I've read them but am not able to understand them) Thx.

I don't know how you'd get that error with this code. This is trying to use a non-static member from inside a static member which is not allowed. An instance is required to invoke an instance member. The fiddle produces an error saying that an instance is required. — Mike Zboray
– Mike Zboray, Commented Sep 19, 2017 at 23:14

John Wu · Accepted Answer · 2017-09-19 23:17:19Z

Either everything has to be static or everything has to be instance. You're getting in trouble because you are mixing and matching.

Everything static:

using System;

public class TestClass
{
    private delegate void TestDelegate();
    static TestDelegate testDelegate;    //<-- static

    static TestClass()                   //<-- static
    {
        testDelegate = new TestDelegate(MyMethod);
    }

    public static void Testit()
    {
        testDelegate();
    }

    private static void MyMethod()
    {
        Console.WriteLine("Foobar");
    }
}

public class Program
{
    public static void Main()
    {
        Console.WriteLine("Hello World");
        TestClass.Testit();
    }
}

Everything instanced:

using System;

public class TestClass
{
    private delegate void TestDelegate();
    TestDelegate testDelegate;

    public TestClass()
    {
        testDelegate = new TestDelegate(MyMethod);
    }

    public void Testit()   
    {
        testDelegate();
    }

    private void MyMethod()
    {
        Console.WriteLine("Foobar");
    }
}

public class Program
{
    public static void Main()
    {
        Console.WriteLine("Hello World");
        var t = new TestClass();
        t.Testit();   //<-- non-static
    }
}

Output (same in both examples):

Hello World
Foobar

Stuart Smith · Accepted Answer · 2017-09-19 23:24:32Z

0

You could use action C# internal delegate. This way you do not have specify the delegate. Then in your static method you could new up your object.

using System;

public class TestClass
{

    Action testDelegate;

    public TestClass()
    {
        testDelegate = new Action(MyMethod);
    }

    public static void Testit()
    {
        TestClass ts = new TestClass();
        ts.testDelegate();
    }

    private void MyMethod()
    {
        Console.WriteLine("Foobar");
    }
}

public class Program
{
    public static void Main()
    {
        Console.WriteLine("Hello World");
        TestClass.Testit();
    }
}

Output:

Hello World
Foobar

answered Sep 19, 2017 at 23:24

Stuart Smith

2,09118 silver badges31 bronze badges

1 Comment

xpt Over a year ago

Thanks for the answer @StuartSmith, I picked the other only because that is one I can understand (I don't know Action)

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