The type or namespace name 'IObservable' could not be found. Are you missing a using or directive or assembly reference?

Question

I'm attempting to implement the IObservable interface in C# using Mono 2.10.6, and Monodevelop 2.8.2, and I keep getting the following error:

The type or namespace name 'IObservable' could not be found. Are you missing a using or directive or assembly reference?

I'm using:

• System
• System.Collections.Generic;
• System.Collections.ObjectModel

I have references to:

• System
• System.Core

Answer 1

Seems that you have to compile for .NET 4.0:

#if NET_4_0

namespace System{
  public interface IObservable<out T>
  {
    IDisposable Subscribe (IObserver<T> observer);
  }
}

#endif

(Taken from this one ).

Maybe you have not set to .NET 4.0 as the target framework?