Debug a dynamically loaded DLL

Question

I have a web app solution (let's say in C:\WebApp). At some point, I need to inject an external DLL from another solution (C:\Custom) and invoke a method in it.

I'm using this code:

public ActionResult ExecuteCustomAction()
{
    Assembly assembly = Assembly.LoadFile(@"C:\Custom\Custom\bin\Debug\Custom.dll");
    Object o = assembly.CreateInstance("Custom.Custom");
    if (o != null)
    {
        MethodInfo method = o.GetType().GetMethod("Execute");
        Object[] ob = // some params
        if (method != null)
        {
            Object returnValue = method.Invoke(o, ob).ToString();
            return new HttpStatusCodeResult(HttpStatusCode.OK);
        }
    }
    return new HttpStatusCodeResult(HttpStatusCode.InternalServerError);
}

No problem until now.

I would like to be able to debug the invoked method (the Custom solution is open in another VS instance), but didn't succeed.

I disabled the "Just my code" option, the Debug/Windows/Modules shows that the symbols for Custom.dll are loaded correctly, I can attach both VS instances (WebApp VS and Custom VS) to the w3wp process, but the execution never stops on the breakpoint I put inside the Execute method.

I'm not familiar with this, am I missing something obvious ?

EDIT: The sources are built locally, I also tried copying them in the app bin folder, referencing this path instead of the original one.

i am not familiar with asp.net but (if possible) i would add a Debbuger.Launch() to the custom.dll so i could call it like o.GetType().GetMethod("LaunchDebugger"); — Sebastian L, Jun 24 '15 at 09:50
Is this DLL compiled in debug mode? Where do you put the breakpoint? — kamil-mrzyglod, Jun 24 '15 at 09:54
@Kamo Yes, it is. and as stated, the main app sees that the symbols for this DLL are loaded. I put the breakpoint inside the invoked method. It never triggers, no matter where it is. — xlecoustillier, Jun 24 '15 at 09:54
@X.L.Ant - Are you sure this `ExecuteCustomAction()` action is called? — kamil-mrzyglod, Jun 24 '15 at 09:59
@Kamo of course :) A breakpoint on `method.Invoke...` stops the execution, but then the next one (i.e. in the Execute method) doesn't. — xlecoustillier, Jun 24 '15 at 10:01
@X.L.Ant - huh I have hard time imagining this tbh. Are we talking about `Execute` method in your external DLL? — kamil-mrzyglod, Jun 24 '15 at 10:03
@X.L.Ant - maybe a silly question but why you load external DLL instead of referencing it in your project? — kamil-mrzyglod, Jun 24 '15 at 10:07
@Kamo Good question : this dll path will be dynamic, intended to work as a plugin. So the project doesn't know about it before runtime. — xlecoustillier, Jun 24 '15 at 10:09
@X.L.Ant - check this topic: http://stackoverflow.com/questions/1295807/debug-dynamically-loaded-assembly-in-visual-studio-net — kamil-mrzyglod, Jun 24 '15 at 10:10
@kamo I already did, to no avail. That's why I think I forgot something silly. — xlecoustillier, Jun 24 '15 at 10:20
Please refer http://stackoverflow.com/questions/1295807/debug-dynamically-loaded-assembly-in-visual-studio-net — Chander .k, Jun 24 '15 at 10:46

score -1 · Answer 1 · answered Jun 24 '15 at 11:01

You should not use a DLL while debugging your code. A DLL is always considered a complete solution that is ready to be used in other program components.

Visual Studio doesn't allow you debugging a DLL that is imported from another project for that purpose.

Your solution is simple; debug your code (by including it in your app), make sure it is working fine, then move it to a separate DLL that is ready for any external usage.

Debug a dynamically loaded DLL

1 Answers1