Can I Combine 2 Different Delegates

Question

1.00/5 (1 vote)

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C#

class Foo
{
    [DllImport("kernel32.dll", EntryPoint = "GetProcAddress")]
    private static extern IntPtr GetProcAddress(IntPtr hModule, string procName);

    public delegate void TestMethod(uint cap);
    public static TestMethod Method;

    static Foo()
    {
        Method = Func<TestMethod>("TestMethod");
    }

    public static T Func<T>(string name) where T : class
    {
        IntPtr _dll = IntPtr.Zero;// ptr to dll

        IntPtr ptr = GetProcAddress(_dll, name);

        Delegate a = Marshal.GetDelegateForFunctionPointer(ptr, typeof(T));

        //Create delegate of type T but with different body of a => { Console.WriteLine("test"); };
        Delegate b;
 
        //Multicast delegate
        return Delegate.Combine(a, b) as T;
    }
}

then

Foo.Method(); // executes the method and writes in console

The point is to wrap the T delegate and add functionality to it.

Can this be done ?

Posted 31-Oct-15 5:23am

petarpetrovt

Updated 31-Oct-15 20:20pm

v8

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Comments

phil.o 31-Oct-15 12:17pm

Noy clear what you intend by combining delegates. Technically, delegates are method pointers. Nothing prevents you from using a delegate as a parameter for another delegate.

petarpetrovt 31-Oct-15 13:08pm

my intention is to wrap a generic delegate and add functionality to it

phil.o 31-Oct-15 13:16pm

I still don't understand. Please give a concrete example.

phil.o 31-Oct-15 13:40pm

Please improve your question with the code. I don't read code in comments, they are not meant for that.

BillWoodruff 31-Oct-15 13:23pm

If your generic method is based on T is a Class, how does returning two "combined" delegates make a Class to return ? Does not make sense ... to me. Please clarify.

petarpetrovt 31-Oct-15 13:26pm

T is System.Delegate

public delegate void GLEnable(uint cap); - > Test< GLEnable >();

BillWoodruff 31-Oct-15 14:10pm

A Delegate is not a Class.

petarpetrovt 31-Oct-15 14:12pm

https://msdn.microsoft.com/en-us/library/system.delegate(v=vs.110).aspx

-> public abstract class Delegate : ICloneable, ISerializable

phil.o 31-Oct-15 16:53pm

The documentation says that "The Delegate class is not considered a delegate type; it is a class used to derive delegate types.". That makes a huge difference.

Krunal Rohit 31-Oct-15 13:32pm

Why ? Why ?

-KR

phil.o 31-Oct-15 16:57pm

Still, I don't get it. What disturbs me is your b variable. A delegate declaration is just useless if you do not specify the signature of the delegate. And the comment "Create delegate from function () => { Console.WriteLine("test"); };" does help me to catch it, either. Sorry.
Func method shouldn't be named like that, since it is ambiguous with System.Func already defined at the root of the framework.

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phil.o · Answer 1 · 2015-10-31T06:23:00

Solution 1

C#

delegate void EnclosingDelegate(string parameter);

delegate string EnclosedDelegate();

class foo
{
   void main() {
      EnclosedDelegate enclosed = () => "foo";
      EnclosingDelegate enclosing = (s) => s = enclosed();
   }
}

Is that what you are searching for?

Posted 31-Oct-15 6:23am

phil.o