how to import a class from dll?

Question

mydll.dll

namespace mydll
{
    public class MyClass {
        public static int Add(int x, int y)
        {
            return x +y;
        }
    }
}

In another project how can I import MyClass or just Add function?

I want to add with DllImport,

[DllImport("mydll.dll", CharSet = CharSet.Auto) ] public static extern .......

how can I do that?

Solution 1

You can use Reflection to load assembly at runtime.

Here a piece of code you can use :

Assembly myAssembly ;
myAssembly = Assembly.LoadFile("myDll.dll");

object o;
Type myType =  myAssembly.GetType("<assembly>.<class>");
o = Activator.CreateInstance(myType);

Here you can find a good tutorial.

Solution 2

DllImport is used to call unmanaged code. The MyClass class you have shown is managed code and in order to call it in another assembly you simply add reference to the assembly containing it and invoke the method. For example:

using System;
using mydll;

class Program
{
    static void Main()
    {
        int result = MyClass.Add(1, 3);
        Console.WriteLine(result);
    }
}

Comments

[Okan Kocyigit]

No I want to add dll while program running, not with add reference option, so how can I create a unmanaged dll?

[Darin Dimitrov]

@ocanal, you could load an assembly at runtime using Reflection and the Assembly.LoadFrom method. Once the assembly is loaded you could list all the types inside and invoke methods on them.