Confessions of a .NET Developer!

How to dynamically load assemblies including unreferenced assemblies

This post will explain how to load the dll dynamically and use the class’s methods in that dll. We will use the Activator class to create an instance of a class from the dll and invoke the required methods. So lets get started.

First of all, create a base class library and name it as AClassLibrary:

ClassLibrary

ClassLibrary

Add a new class named AClass, it will look like this:

    public class AClass
    {
        public void WriteDefault()
        {
            Console.WriteLine("A text");
        }

        public void WriteIt(string text)
        {
            Console.WriteLine(text);
        }

        public void WriteIt(string text1, string text2)
        {
            Console.WriteLine(text1 + text2);
        }
    }

Do note that we have two overloaded functions named WriteIt, I will let you know its significance later.

Now lets create another Console Application project in the same solution named CaptureAssembly.
After that, Add Reference to the project AClassLibrary:

AddReference

AddReference

Before explaining, let me show you the whole code:

using System;
using System.Reflection;

namespace CaptureAssembly
{
    class Program
    {
        static void Main(string[] args)
        {
            Assembly a = Assembly.LoadFrom("AClassLibrary.dll");

            Type clsType = a.GetType("AClassLibrary.AClass");
            
            //Create the instance of the class
            object clsInstance = Activator.CreateInstance(clsType, null);

            //Calls the WriteDefault method of AClass
            clsType.InvokeMember("WriteDefault", BindingFlags.InvokeMethod, null, clsInstance, null);

            //Calls the WriteIt methods
            clsType.InvokeMember("WriteIt", BindingFlags.InvokeMethod, null, clsInstance, new object[] { "Hello", " Tarun Kumar" });
            clsType.InvokeMember("WriteIt", BindingFlags.InvokeMethod, null, clsInstance, new object[] { "Hello" });

            Console.ReadLine();
        }
    }
}

First we get the type of AClass using the Reflection. The Activator class will use it to create the instance of the class which we name it as clsInstance.
Next step is to call the 3 methods of AClass. We will use the InvokeMember property using clsType. Let’s take the case of the fist InvokeMethod. The first parameter will take the name of the method, second will help us streamline the search for the method as Reflection is used for this purpose. Third parameter is of no use for now. Fourth parameter, the target is the class instance named clsIntance and the last parameter will take the array of objects used to pass the parameters for the method, as WriteDefault doesn’t have any parameters, hence it will remain null.
The next two invoke methods is for the two overloaded methods WriteIt, the first one will call the method which has two parameters as we are passing two items in the object array(last parameter). As the second invoke method has one item in the object array, hence WriteIt(string text) will be called.

And here is the result:

Result

Result

For loading Unreferenced Assemblies

You can also load the assembly without adding any reference. Suppose the base class library(dll) is in some location, then we can use Assembly.LoadFile method to load the assembly.

Just replace

Assembly a = Assembly.LoadFrom("AClassLibrary.dll");

with

Assembly a = Assembly.LoadFile(@"C:\AClassLibrary\bin\Debug\AClassLibrary.dll");

and you will get the same result.

Happy coding!

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June 30, 2011 - Posted by | C Sharp, Winforms, WPF

1 Comment »

  1. Well written and explained. Very good resource for beginner.

    Comment by Chankya | July 21, 2011 | Reply


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