use Type.GetType(string) in C# 2.0 .net but type or namespace name 't' could not be found

Question

I'm not sure how to correct this. I have

public void get_json(String TYPE) { Type t = Type.GetType("campusMap." + TYPE); t[] all_tag = ActiveRecordBase<t>.FindAll(); }

But I always just get

Error 9 The type or namespace name 't' could not be found (are you missing a using directive or an assembly reference?) C:_SVN_\campusMap\campusMap\Controllers\publicController.cs 109 17 campusMap

any ideas on why if I'm defining the type I am wishing to gain access to is saying it's not working? I have tried using reflection to do this with no luck. Anyone able to provide a solution example?

[EDIT] possible solution

This is trying to use the reflection and so I'd pass the string and invoke the mothod with the generic.

 public void get_json(String TYPE) { CancelView(); CancelLayout(); Type t = Type.GetType(TYPE); MethodInfo method = t.GetMethod("get_json_data"); MethodInfo generic = method.MakeGenericMethod(t); generic.Invoke(this, null); } public void get_json_data<t>() { t[] all_tag = ActiveRecordBase<t>.FindAll(); List<JsonAutoComplete> tag_list = new List<JsonAutoComplete>(); foreach (t tag in all_tag) { JsonAutoComplete obj = new JsonAutoComplete(); obj.id = tag.id; obj.label = tag.name; obj.value = tag.name; tag_list.Add(obj); } RenderText(JsonConvert.SerializeObject(tag_list)); }

and the error I get is in..

 obj.id = tag.id;

of 't' does not contain a definition for 'id'

and same for the two name ones.

The problem is the same - trying to use a Type variable as a generic type argument, and your problem would be fixed by the solutions in the answers; specifically, stackoverflow.com/a/2604844/79439 — thecoop
– thecoop, Commented Dec 20, 2011 at 18:04
I don't know.. That answer may be clear to you but Digitlworld's seems more clear to me here .. :/ why I'm working this out, just not sure how to use that one you pointed out. — Quantum
– Quantum, Commented Dec 20, 2011 at 18:06
The additional problem here is you're using a generic type in a way that the compiler would have to know ahead of time the members it contains. It can't find tag.id, because it doesn't know, not really, what the type of tag is. The other pitfall is that the t in MethodInfo method = t.GetMethod("get_json_data"); needs to be whatever type that get_json_data<t> is declared in. You should probably read up on both reflection and generics. It's a very broad topic, but for what you're trying to do, a clear understanding of both topics is paramount. — digitlworld
– digitlworld, Commented Dec 20, 2011 at 19:57

Community · Accepted Answer · 2017-05-23 11:55:31Z

You can't pass a variable in as a generic parameter:

t[] all_tag = ActiveRecordBase<t>.FindAll();

It's complaining about the <t> part. You can't do that.

I suggest you check this out: How do I use reflection to call a generic method?

Outside of that, I'd probably do everything you want to do with the generic type in a generic method, and then use reflection to call that generic function with the runtime type variable.

public void get_json<t>() { t[] all_tag = ActiveRecordBase<t>.FindAll(); //Other stuff that needs to use the t type. }

And then use the reflection tricks in the linked SO answer to call the get_json function with the generic parameter.

MethodInfo method = typeof(Sample).GetMethod("get_json"); MethodInfo generic = method.MakeGenericMethod(typeVariable); generic.Invoke(this, null);

I edited the question to reflect the possible suggestiong here. tk
"You can't pass a variable in as a generic parameter" Is fully right... and What I ended up doing was setting up an interface and then made the the class types I needed to call from the parameter the and they inherite from that.

Eric Lippert · Accepted Answer · 2011-12-20 17:13:41Z

Your program indicates a fundamental misunderstanding about how C# works. The type of all_tag and the type value of the type argument must both be known to the compiler before the program is compiled; you do not determine that type until the program is already running, which clearly is after it is compiled.

You can't mix static compile-time typing with dynamic runtime typing like this. Once you are doing something with Reflection, the whole thing has to use Reflection.

No I get that it is supost to be "knowen" .. but that is not what the need is. the point is that I have to have a dynamic part here, or face 35+ copy pasting of the same 6 line method where I only change <t> ... and that seems like C# has to have a solution too that is clean and clear. I know moving to 3.5 would give dynamic types but we can't do that. Open to ideas :D

Community · Accepted Answer · 2017-05-23 12:11:59Z

Can you delegate the choice of type to the calling code? You can't specify a runtime type as a generic, compile-time type, but if you could delegate the choice of type to the caller, you might be able to accomplish what you want.

public ??? get_json<T>() // seems like this should return something, not void { var collection = ActiveRecord<T>.FindAll(); // do something with the collection }

Called as

get_json<CampusMap.Foo>();

Even if you didn't know the type at compile time, it ~~might~~ would be easier to call this way via reflection, see https://stackoverflow.com/a/232621.

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use Type.GetType(string) in C# 2.0 .net but type or namespace name 't' could not be found

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