Question

I am trying to come up with a method factory that looks inside config to get the full name of the type to instantiate and creates that object type dynamically.

Here is my Type and the Interface:

public interface IComponent<T> 
{
    IEnumerable<T> DataSource {get; set;}

    void PerformTask(object executionContext);

}

namespace MyCompany.Components 
{
    public class ConcreteComponent1<T> : IComponent<T> 
    {

        private IEnumerable<Contact> contactSource = null;

        internal ConcreteComponent1() {}

        public void PerformTask(object executionContext) 
        {
            this.contactSource = GetSource(executionContext);

            foreach(var result in this.contactSource) 
            {
                result.Execute(executionContext); 
            }
        }

        public IEnumerable<T> DataSource 
        {
            get { return this.contactSource as IEnumerable<T>; }
            set { this.contactSource = (IContactSource)value; }
        }
    }
}

Factory, resides in the same assembly:

//Factory - Same assembly
public static class ComponentFactory<T> 
{
    public static IComponent<T> CreateComponent() 
    {
        var assembly = Assembly.GetExecutingAssembly();
        object o = assembly.CreateInstance("MyCompany.Components.ConcreteComponent1"); //o is null...

        var objectHandle = Activator.CreateInstance(Assembly.GetAssembl(typeof(ComponentFactory<T>)).GetName().FullName, "MyCompany.Components.ConcreteComponent1"); //throws Could not load type from assembly exception.                     
        return o as IComponent<T>;
    }
}

So in first case the o is always null.

In the second case when using the Activator class, it throws Type could not be loaded from assembly “MyAssembly”. No inner exception. What am I doing wrong?

Answer 1

First of all, actual name of your type is:

MyCompany.Components.ConcreteComponent1`1

It can’t be instantiated because you have to specify type parameters:

public static class ComponentFactory<T>
{
    public static IComponent<T> CreateComponent()
    {
        Type generic = Type.GetType("MyCompany.Components.ConcreteComponent1`1");
        Type concrete = generic.MakeGenericType(typeof(T));
        var objectHandle = Activator.CreateInstance(
           concrete,
           BindingFlags.NonPublic | BindingFlags.Instance,
           null,
           null, //here can come ctor params
           null); 
        return objectHandle as IComponent<T>;
    }
}

this will work with internal constructor.