在C＃2.0 .net中使用Type.GetType（string），但找不到类型或名称空间名称't'

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.

Answer 1

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);

Answer 2

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.

Answer 3

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 .