'System.Collections.Generic.IList<object>' does not contain a definition for 'Add' when using 'dynamic' and 'ExpandoObject'

Question

Say that I have a class, Foo, looking something like this:

public class Foo : IFoo
{
    public Foo()
    {
        Bars = new List();
    }
    p         


        

Answer 1

This is a known dynamic binding issue.

Here are some work arounds.

Use ICollection instead:

void Main()
{
    IFoo foo = new Foo();
    dynamic a = new System.Dynamic.ExpandoObject();
    a.Prop = 10000;
    dynamic b = new System.Dynamic.ExpandoObject();
    b.Prop = "Some Text";
    foo.Bars.Add(a);
    foo.Bars.Add(b); 
}

public interface IFoo
{
    ICollection Bars { get; set; }
}

public class Foo : IFoo
{
    public Foo()
    {
        Bars = new List();
    }

    public ICollection Bars { get; set; }
}

Or straight up List:

public interface IFoo
{
    List Bars { get; set; }
}

public class Foo : IFoo
{
    public Foo()
    {
        Bars = new List();
    }

    public List Bars { get; set; }
}

Or use dynamic foo:

void Main()
{
    dynamic foo = new Foo();
    dynamic a = new System.Dynamic.ExpandoObject();
    a.Prop = 10000;
    dynamic b = new System.Dynamic.ExpandoObject();
    b.Prop = "Some Text";
    foo.Bars.Add(a);
    foo.Bars.Add(b); 
}

Or don't dynamic bind add, by casting to object:

void Main()
{
    IFoo foo = new Foo();
    dynamic a = new System.Dynamic.ExpandoObject();
    a.Prop = 10000;
    dynamic b = new System.Dynamic.ExpandoObject();
    b.Prop = "Some Text";
    foo.Bars.Add((object)a); 
    foo.Bars.Add((object)b); 
}

Or be more expressive using a third party framework like my impromptu interface with ActLike & Prototype Builder Syntax (in nuget).

using ImprmoptuInterface;
using Dynamitey;
void Main()
{
    dynamic New = Builder.New();

    IFoo foo = Impromptu.ActLike(
                   New.Foo(
                       Bars: New.List(
                                 New.Obj(Prop:10000),
                                 New.Obj(Prop:"Some Text")
                             )
                       )
                   );
}

public interface IFoo
{
    IList Bars { get; set; }
}