Question

How can I set generic type dynamically?

 public class A
    {
        public int X { get; set; }

        public A()
        {
            X = 9000;
        }
    }

    public class Class1
    {

        public void Test()
        {
            List<A> theList = new List<A>() {
                new A { X = 1 },
                new A { X = 2 }               
            };


            object testObj = theList;
            var argType = testObj.GetType().GetGenericArguments()[0];


            Foo(testObj as ICollection<argType>); // ?                                           

        }

        public void Foo<T>(ICollection<T> items) where T:new()
        {
            T newItem = new T();    
            items.Add(newItem);    

        }

Answer 1

To do in “regular” c# you would use reflection to obtain the MethodInfo, then use MakeGenericMethod() and Invoke(). However, this is easier:

Foo((dynamic)testObj);

The reflection approach here is:

var method = typeof(Class1).GetMethod("Foo").MakeGenericMethod(argType);
method.Invoke(this, new object[] { testObj });