DynamicActivity Class (System.Activities)

// Variables
var iterationVariable = new DelegateInArgument<int>() { Name = "iterationVariable" };
var accumulator = new Variable<int>() { Default = 0, Name = "accumulator" };

// Define the Input and Output arguments that the DynamicActivity binds to
var numbers = new InArgument<List<int>>();
var average = new OutArgument<double>();

var result = new Variable<double>() { Name = "result" };

return new DynamicActivity()
{
    DisplayName = "Find average",
    Properties = 
    {
        // Input argument
        new DynamicActivityProperty
        {
            Name = "Numbers",
            Type = typeof(InArgument<List<int>>),
            Value = numbers
        },
        // Output argument
        new DynamicActivityProperty
        {
            Name = "Average",
            Type = typeof(OutArgument<double>),
            Value = average
        }
    },
    Implementation = () =>
        new Sequence
        {
            Variables = { result, accumulator },
            Activities =
            {
                new ForEach<int>
                {
                    Values =  new ArgumentValue<IEnumerable<int>> { ArgumentName = "Numbers" },                                
                    Body = new ActivityAction<int>
                    {
                        Argument = iterationVariable,
                        Handler = new Assign<int>
                        {
                            To = accumulator,
                            Value = new InArgument<int>(env => iterationVariable.Get(env) +  accumulator.Get(env))
                        }
                    }
                },

                // Calculate the average and assign to the output argument.
                new Assign<double>
                {
                    To = new ArgumentReference<double> { ArgumentName = "Average" },
                    Value = new InArgument<double>(env => accumulator.Get(env) / numbers.Get(env).Count<int>())
                },
            }
        }