Create instance from string class name

Question

Is there a way to achieve this? I have a class name that I pass via query string and I want to make a new instance based on that.

What I have tried:

Private Function Carregar() As Object
    Dim bal = String.Concat("PROTBAL.", Request.QueryString("nomeBAL"))
    Dim ent = Request.QueryString("nomeENT")
    Dim codigo = Request.QueryString("codigo")
    Dim descricao = Request.QueryString("descricao")
    Dim teste = Activator.CreateInstance(Type.GetType(bal))
    Return teste.Listar()
End Function

The thing is the variable teste is always Nothing.

You may find this interesting: stackoverflow.com/a/11107562/897326. — Victor Zakharov
– Victor Zakharov, Commented Feb 3, 2014 at 18:55
You might want to check that bal contains the name of a class which you want to allow to have an instance of created. — Andrew Morton
– Andrew Morton, Commented Feb 3, 2014 at 19:09
Yeah, I saw that one, but I couldn't recreate it. All I get is "Nothing". @Neolisk — Vic Wolk
– Vic Wolk, Commented Feb 3, 2014 at 19:13
Yes, it does. It pops as a string with "PROTBAL.NameOfMyClass". @AndrewMorton — Vic Wolk
– Vic Wolk, Commented Feb 3, 2014 at 19:16
I can't see why it would not work. You can try in a brand new WinForms application. If you can successfully call it there - there may be something wrong with your web project (usually a namespace issue). — Victor Zakharov
– Victor Zakharov, Commented Feb 3, 2014 at 19:39

Ňɏssa Pøngjǣrdenlarp · Accepted Answer · 2014-02-03 19:29:23Z

1

assuming you concat the class name correctly, this should work:

System.Reflection.Assembly.GetExecutingAssembly().CreateInstance(bal)

Edit

If the type (class) can/may be in another assembly, then this works:

System.Reflection.Assembly.GetAssembly(bal).CreateInstance(bal)

but I am not sure that will work eitehr - I did not notice the dot operator in the name - is this an internal class or namespace ref? I dont think you can resolve internal classes that way. If you could create a method on PROTBAL like CreateNewThing you could do away with all this and just call the method with an arg to indicate which type you want (since PROTBAL is known).

edited Feb 3, 2014 at 19:29

answered Feb 3, 2014 at 18:53

Ňɏssa Pøngjǣrdenlarp

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3 Comments

Vic Wolk Over a year ago

Still "Nothing". Is it an issue that the "ExecutingAssembly" is not where the class I'm passing actually is? For instance, I get "PROTInterface" from that, and the class I want is at "PROTBAL".

Vic Wolk Over a year ago

I'm kinda lost now. That doesn't even seem to compile. The thing is... PROTBAL is a namespace in which I have several classes I need and am passing the chosen names via query string. All this action is taken at another namespace's class.

Ňɏssa Pøngjǣrdenlarp Over a year ago

sorry, GetAssembly takes a Type param...which if you knew that, we would not be here.

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