using System;

​

public class ValueChangedArgs : EventArgs

{

    public readonly int OldV;

    public readonly int NewV;

    public ValueChangedArgs(int oldV, int newV)

    {

        OldV = oldV;

        NewV = newV;

    }

}

​

public class MyValue

{

    private int value = 0;

    public event EventHandler<ValueChangedArgs> onValueChanged = null;

    private void valueChangedHandler(int oldV, int newV)

    {

        if (onValueChanged != null)

            onValueChanged(this, new ValueChangedArgs(oldV, newV));

    }

​

    public int Value

    {

        get

        {

            return value;

        }

​

        set

        {

            if (value != this.value)

            {

                int temp = this.value;

                this.value = value;

                valueChangedHandler(temp, value);

            }

        }

    }

}

​

public class ValueChangeObserver

{

    public ValueChangeObserver(MyValue v)

    {

        v.onValueChanged += myOnValueChanged;

    }

​

    private void myOnValueChanged(object sender, ValueChangedArgs args)

    {

        Console.WriteLine("Value changed by {0}", args.NewV - args.OldV);

    }

}

​

public class ValueAverageChangeObserver

{

    private int sum = 0, count = 0;

    public ValueAverageChangeObserver(MyValue v)

    {

        v.onValueChanged += myOnValueChanged;

    }

​

    private void myOnValueChanged(object sender, ValueChangedArgs args)

    {

        count++;

        sum += args.NewV - args.OldV;

        Console.WriteLine("Value average change is {0:F}",(double)sum / (double)count);

    }

}

​

public class Program

{

    public void Main(string[] args)

    {

        MyValue v = new MyValue();

        new ValueChangeObserver(v);

        new ValueAverageChangeObserver(v);

        Console.WriteLine(v);

        v.Value = 100;

        v.Value = 210;

        v.Value = 150;

        v.Value = 180;

    }

}