Invoke Method inside another DLL in a asp.net project WITH a namespace

Question

We have an asp.net 4.7 project and we're trying to call a method in another dll file ( from one of the dll files inside /Bin )

This is how the project structure looks:

Our Main project

Sub project: Asp.net Project - hosted on a webserver
Another sub project called WA.Core.Framework
Another sub project called WA.Core.Libary
Another sub project callde WA.Extension.Pages

When compiling the project all the files will automatically be copied to the Asp.net project folder /Bin

Image

In our Library project we have the invoke method:

    public string InvokeString(string typeName, string methodName)
    {
        Type calledType = Type.GetType(typeName);

        String s = (String)calledType.InvokeMember(
                        methodName,
                        BindingFlags.InvokeMethod | BindingFlags.Public,
                        null,
                        null,
                        null);

        return s;
    }

And in the framework project we have the function that calls the method we want to call:

new Lib_Invoke().InvokeString("WA.Extension.Pages.Extension", "Init");

And last in our WA.Extension.Pages we have:

namespace WA.Extension.Pages
    {
        public class Extension
        {
            public void Init()
            {
                HttpContext.Current.Response.Write("hello from extension");

            }
        }
    }

But so far all it gives me is

System.NullReferenceException: Object reference not set to an instance of an object.

I have double checked the references and should work.

EDIT:

After playing around with it and with the help from this thread, I ended up with this:

    public string InvokeString(string assemblyName, string namespaceName, string typeName, string methodName)
    {
        Type calledType = Type.GetType(namespaceName + "." + typeName + "," + assemblyName);

        String s = (String)calledType.InvokeMember(
                        methodName,
                        BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Instance,
                        null,
                        Activator.CreateInstance(calledType),
                        null);
        return s;
    }

One of the important things that was added was the asambly name and Activator.CreateInstance(calledType) in the bindingflags.

So when I want to call the method:

new Lib_Invoke().InvokeString("WA.Extension.Pages", "WA.Extension.Pages", "Extension", "Init");

Thanks for your help!

Is the dll actually loaded, or is it just sitting int he directory? is it referenced, you need more informatiuon — TheGeneral, Sep 02 '18 at 02:12
Updated the description a little. Hope it's better. Thanks. + Yeah, I'm able to use the method normally from an asp.net page or if I use the /App_Code. — ClausDK, Sep 02 '18 at 02:26
Possible duplicate of [Type.GetType("namespace.a.b.ClassName") returns null](https://stackoverflow.com/questions/1825147/type-gettypenamespace-a-b-classname-returns-null) — Alejandro, Sep 02 '18 at 02:36

score 0 · Accepted Answer · answered Sep 02 '18 at 02:50

Init() is an instance(non-static) method in your example. You should add BindingFlag.Instance and provide target object of type Extension:

public static string InvokeString(string typeName, string methodName)
{
    Type calledType = Type.GetType(typeName);            

    String s = (String)calledType.InvokeMember(
                    methodName,
                    BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Instance,
                    null,
                    Activator.CreateInstance(calledType),
                    null);

    return s;
}

Or you can mark Init() method as static:

public static void Init()
{
    HttpContext.Current.Response.Write("hello from extension");
}

and add just a BindingFlag.Static:

public static string InvokeString(string typeName, string methodName)
{
    Type calledType = Type.GetType(typeName);            

    String s = (String)calledType.InvokeMember(
                    methodName,
                    BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Static,
                    null,
                    null,
                    null);

    return s;
}

After that try to debug the Init() method. I suspect that HttpContext.Current may be null. In this case you can pass HttpContext instance as argument to through InvokeMember:

public static void Init(HttpContext ctx)
{
    ctx.Response.Write("hello from extension");
}

and:

public static string InvokeString(string typeName, string methodName)
{
    Type calledType = Type.GetType(typeName);            

    String s = (String)calledType.InvokeMember(
                    methodName,
                    BindingFlags.InvokeMethod | BindingFlags.Public | BindingFlags.Static,
                    null,
                    null,
                    new object[] { HttpContext.Current });

    return s;
}

Hope it helps.

Thanks for your help. Turns out it was a combo of 2 tings. I changed code so it includes the asambly name after the , in the typeName. And the BindingFlags.Instance + Activator.CreateInstance(calledType) in the InvokeMember configuration — ClausDK, Sep 02 '18 at 03:58

Invoke Method inside another DLL in a asp.net project WITH a namespace

1 Answers1