System.MemberAccessException – Cannot create an instance of type ‘xyz’

The System.MemberAccessException with the message “Cannot create an instance of type ‘xyz'” occurs in C# when you attempt to create an instance of a type, but the runtime is unable to do so. This typically happens due to restrictions on the type, such as it being abstract, an interface, or lacking a parameterless constructor.

Common Causes and Solutions

1. Abstract Classes or Interfaces:
   You cannot create an instance of an abstract class or an interface.

   public abstract class Example { }

   var instance = Activator.CreateInstance(typeof(Example)); // MemberAccessException – Cannot instantiate abstract class

Fix: Instantiate a concrete subclass instead.

   public class ConcreteExample : Example { }

   var instance = Activator.CreateInstance(typeof(ConcreteExample)); // Works correctly

2. No Parameterless Constructor:
   If the type does not have a parameterless constructor and you attempt to create an instance without providing arguments, this exception will occur.

   public class Example
   {
       public Example(string message) { }
   }

   var instance = Activator.CreateInstance(typeof(Example)); // MemberAccessException – No parameterless constructor

Fix: Provide the required constructor arguments.

   var instance = Activator.CreateInstance(typeof(Example), "Hello"); // Works correctly

3. Private or Internal Constructors:
   If the constructor is private or internal and you do not have the necessary permissions to access it, this exception can occur.

   public class Example
   {
       private Example() { }
   }

   var instance = Activator.CreateInstance(typeof(Example)); // MemberAccessException – Cannot access private constructor

Fix: Use reflection with BindingFlags to access non-public constructors.

   var constructor = typeof(Example).GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance, null, Type.EmptyTypes, null);
   var instance = constructor.Invoke(null); // Works correctly

4. Generic Types:
   If you attempt to create an instance of an open generic type (without specifying type arguments), this exception will occur.

   public class Example<T> { }

   var instance = Activator.CreateInstance(typeof(Example<>)); // MemberAccessException – Cannot instantiate open generic type

Fix: Provide the type arguments for the generic type.

   var instance = Activator.CreateInstance(typeof(Example<int>)); // Works correctly

5. Static Classes:
   You cannot create an instance of a static class.

   public static class Example { }

   var instance = Activator.CreateInstance(typeof(Example)); // MemberAccessException – Cannot instantiate static class

Fix: Static classes cannot be instantiated. Use the class directly.

   Example.SomeMethod(); // Use the static class directly

6. Type Initialization Issues:
   If the type’s static constructor or initialization logic throws an exception, this can prevent the type from being instantiated.

   public class Example
   {
       static Example() => throw new Exception("Static constructor failed");
   }

   var instance = Activator.CreateInstance(typeof(Example)); // MemberAccessException – Type initialization failed

Fix: Fix the static constructor or initialization logic.

   public class Example
   {
       static Example() { /* Fix the logic */ }
   }

7. Restricted Types:
   Certain types, such as System.Void or pointer types, cannot be instantiated.

   var instance = Activator.CreateInstance(typeof(void)); // MemberAccessException – Cannot instantiate void

Fix: Avoid attempting to instantiate restricted types.