Using AppDomain in C# to dynamically load and unload dll

In one of my application, which is related to system diagnostics, the related DLL is to be loaded and unloaded dynamically in C#. After some search I found that a separate DLL cannot be loaded dynamically its the complete AppDomain. So I have to create an AppDomain and use that DLL to be loaded unloaded dynamically. But I could not find anywhere how can I use that in code. I can not show the app code since it is against company rules.

Can somebody tell me some application code to use it. I want to load and unload the dll dynamically using appdomain and call a specific method in that dll, the dll does not have any entry point.

Thanks for answers. Ashutosh

How to: Load Assemblies into an Application Domain

public static void Main()


    {
        // Use the file name to load the assembly into the current
        // application domain.
        Assembly a = Assembly.Load("example");
        // Get the type to use.
        Type myType = a.GetType("Example");
        // Get the method to call.
        MethodInfo myMethod = myType.GetMethod("MethodA");
        // Create an instance.
        object obj = Activator.CreateInstance(myType);
        // Execute the method.
        myMethod.Invoke(obj, null);
    }

As for how to unload it, you have to unload the AppDomain itself, see this

AppDomain Temporary = AppDomain.CreateDomain("Temporary");
try
{
  Gateway Proxy = 
    (Gateway) Temporary.CreateInstanceAndUnwrap("Shim", "Shim.Gateway");

  Match M = Proxy.LoadAndMatch("Plugin.dll", 
    "Though the tough cough and hiccough, plough them through");  
}
finally
{
  AppDomain.Unload(Temporary);
}

It's difficult to understand your question, but I will try to make some suggestions.

There is no reason you cannot dynamically Load a dll directly into your application w/o a separate App Domain, the trick is that you cannot unload it. This is only important if you may load multiple versions of the same dll (i.e. you want the ability to update this diagnostic component to a new version without halting the execution of your application). If that is what you are trying to do, then I suggest this CodeProject article.

Actually you can dynamically load assemblies into your app domain and run code from it, the issue is that you cannot then unload the assembly. You can however load additional app domains (and assemblies into them) and unload the app domain when you are done.

As its name suggests though, you then have a new application domain, and you can't just simply call its code and use its types you need to marshal your calls and data across the domain boundaries. If you search you will find lots of examples on how to do this.

Something to consider though, is that this is a common pattern, and there are ready made solutions for it, the framework itself has a whole addin namespace that is dedicated to this type of plug-in behavior, it might be worth your while in having a close look at that first. There is an article here that shows how to use it.