How do I use a variable of type Type as a Type?

Question

I have a foreach loop running on a list of types. Passing in a variable of type Type as a Type fails outright. Based on similar questions seen on this site, I wrote up a reflection-powered solution but this fails at runtime. I do not know how to proceed from this point.

foreach (Type defType in GenDefDatabase.AllDefTypesWithDatabases())
{   
    // Compile Error: 'defType' is a variable but is used like a type
    DefDatabase<defType>.ResolveAllReferences(); 
    // Runtime Error: System.ArgumentException: The method has 0 generic parameter(s) but 1 generic argument(s) were provided.
    //   at System.Reflection.MonoMethod.MakeGenericMethod (System.Type[] methodInstantiation) [0x00000] in <filename unknown>:0
    typeof(DefDatabase<>).GetMethod("ResolveAllReferences", BindingFlags.Public | BindingFlags.Static).MakeGenericMethod(defType).Invoke(null, null);
}

Possible duplicate of [How do I use reflection to call a generic method?](https://stackoverflow.com/questions/232535/how-do-i-use-reflection-to-call-a-generic-method) — just-my-name, Aug 04 '19 at 05:37
@just-my-name: the problem is that they are trying to call a generic method, even though the method is _not_ in fact generic. See my answer below. — Peter Duniho, Aug 04 '19 at 05:39
@PeterDuniho I see, the type itself is generic, thanks for pointing that out. — just-my-name, Aug 04 '19 at 05:40

score 2 · Accepted Answer · answered Aug 04 '19 at 05:38

In this statement:

typeof(DefDatabase<>).GetMethod("ResolveAllReferences",
    BindingFlags.Public | BindingFlags.Static).MakeGenericMethod(defType).Invoke(null, null);

You are trying to make a generic method. But the thing that's generic is the type, not the method. You should be calling Type.MakeGenericType() instead:

typeof(DefDatabase<>).MakeGenericType(defType).GetMethod("ResolveAllReferences",
    BindingFlags.Public | BindingFlags.Static).Invoke(null, null);

How do I use a variable of type Type as a Type?

1 Answers1