C# Using Assembly to call a method within a DLL

Question

I have been reading a lot about this - I feel like I'm very close to the answer. I am simply looking to call a method from within a dll file that I have created.

For example purposes:

My DLL File:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ExampleDLL
{
    class Program
    {
        static void Main(string[] args)
        {
            System.Windows.Forms.MessageBox.Show(args[0]);
        }

        public void myVoid(string foo)
        {
            System.Windows.Forms.MessageBox.Show(foo);
        }
    }
}

My Application:

string filename = @"C:\Test.dll";
    Assembly SampleAssembly;
    SampleAssembly = Assembly.LoadFrom(filename);
    // Obtain a reference to a method known to exist in assembly.
    MethodInfo Method = SampleAssembly.GetTypes()[0].GetMethod("myVoid");
    // Obtain a reference to the parameters collection of the MethodInfo instance.

All credits go to SO user 'woohoo' for the above snippet How to call a Managed DLL File in C#?

Now, though, I would like to be able to not only reference my Dll (and the methods inside it) but properly call the methods inside it (in this case I would like to call method 'myVoid').

Might anyone have any suggestions for me?

Thank you,

Evan

Answer 1

The question and answer you reference is using reflection to call the method in the managed DLL. This isn't necessary if, as you say you want to do, you simply reference your DLL. Add the reference (via the Add Reference option in Visual Studio), and you can call your method directly like so:

ExampleDLL.Program p = new ExampleDLL.Program(); // get an instance of `Program`
p.myVoid(); // call the method `myVoid`

If you want to go the reflection route (as given by woohoo), you still need an instance of your Program class.

Assembly SampleAssembly = Assembly.LoadFrom(filename);
Type myType = SampleAssembly.GetTypes()[0];
MethodInfo Method = myType.GetMethod("myVoid");
object myInstance = Activator.CreateInstance(myType);
Method.Invoke(myInstance, null);

Now you have an instance of Program and can call myVoid.

Answer 2

Just add this line of code after you obtain reference to your method.

            Method.Invoke(classInstance, new object[] {});

Hope this help.

Answer 3

//Assembly1.dll
using System;
using System.Reflection;

namespace TestAssembly
{
    public class Main
    {
        public void Run(string parameters)
        {
            // Do something... 
        }
        public void TestNoParameters()
        {
            // Do something... 
        }
    }
}

//Executing Assembly.exe
public class TestReflection
{
    public void Test(string methodName)
    {
        Assembly assembly = Assembly.LoadFile("...Assembly1.dll");
        Type type = assembly.GetType("TestAssembly.Main");
        if (type != null)
        {
            MethodInfo methodInfo = type.GetMethod(methodName);
            if (methodInfo != null)
            {
                object result = null;
                ParameterInfo[] parameters = methodInfo.GetParameters();
                object classInstance = Activator.CreateInstance(type, null);
                if (parameters.Length == 0)
                {
                    result = methodInfo.Invoke(classInstance, null);
                }
                else
                {
                    object[] parametersArray = new object[] { "Hello" };

                    result = methodInfo.Invoke(classInstance, parametersArray);
                }
            }
        }
    }
}

Answer 4

MethodInfo has a method called Invoke. So simply call Method.Invoke() with an object you created by for example calling System.Activator.CreateInstance()