从PropertyInfo创建通用列表<Type>

Question

In one of my classes I have the following property:

public List<ClassP> MyPlanes { get; set; }

In another method I have a the propertyInfo of the property above (the function self does not know where the propertyinfo comes from). Right now i'm trying to create a list of classP when i only have the propertyInfo of MyPlanes . So far my attempts seem to be in vain, this is howfar i got sofar:

variable prop is the PropertyInfo of MyPlanes

public void GenerateList(PropertyInfo prop)
{
            if (prop.PropertyType.IsGenericType && prop.PropertyType.GetGenericArguments().Length > 0)
            { 
                List<prop.PropertyType.GetGenericArguments().First()> myValueList = 
                    new List<prop.PropertyType.GetGenericArguments().First()>();
            }
}

The creating of the list (with the code above) gives the following error Using the generic type 'System.Collections.Generic.List<T>' requires 1 type arguments

Any help would be greatly appreciated

Note: I want the list creating in a syntax (or a syntax similar) as visible above. I want to keep my code as generic as possible

Answer 1

To make a generic class when you have the type, you can't use the brackets <> because you don't know the type at compile time. You need to do something like this:

var baseType = typeof(List<>);
var genericType = baseType.MakeGenericType(prop.PropertyType.GetGenericArguments().First());

Now you have the correct type and you can create it like so:

IList myList = (IList)Activator.CreateInstance(genericType);

Edit: although as Selman22 says above, you already have the PropertyType , so you don't need to get the generic type unless you are trying to make a different generic class with the same generic argument (say you have a List<T> and need to make a Dictionary<Type,T> or something). So I'll leave my answer in case you encounter that situation.

Answer 2

Unfortunutely, it does not work like that.You need to use Reflection to create a new instance as well:

var list = (List<ClassP>)Activator.CreateInstance(prop.PropertyType);

CreateInstance method returns object . If you don't know the type at compile time, there is no way to cast it. Best thing you can to would be using dynamic .And that way you can access any members without any compile time error, but clearly it's not safe.

You should probably reconsider whether you really need to use Reflection here.If your problem can be solved without using Reflection then you should go with that way.