Doing reactive/data-flow programming in C# is ludicrously verbose.

Single Reactive Property

    public class DrawingFeature : Feature {
        public ReactiveProperty<Drawing> Drawing = new ReactiveProperty<Drawing>(this.OnFeatureChanged);
    }

    // use: theDrawingFeature.Drawing.It = ...;
    //      theDrawingFeature.Drawing.Change += new EventHandler( ... );


    public class ReactiveProperty<T>
    {
        public ReactiveProperty(ParentChange del)
        {
            parent_ = del;
        }
        private ParentChange parent_;
        private T it_;
        public event EventHandler Changed;
        private bool inChanged_;
        protected void OnChanged()
        {
            if (!inChanged_)
            {
                inChanged_ = true;
                try
                {
                    if (Changed != null)
                    {
                        Changed(this, EventArgs.Empty);
                    }
                    if (parent_)
                    {
                        parent_();
                    }
                }
                finally
                {
                    inChanged_ = false;
                }
            }
        }
        public T It
        {
            get
            {
                return it_;
            }
            set
            {
                it_ = value;
                OnChanged();
            }
        }
    }

    public delegate void ParentChanged();