Observer Design Pattern : Observer Pattern : Design Patterns C# Examples

    
using  System;

public  class  ValueChangedEventArgs  :  EventArgs
{
        public  readonly  int  OldValue,  NewValue;

        public  ValueChangedEventArgs(int  oldTemp,  int  newTemp)
        {
                OldValue  =  oldTemp;
                NewValue  =  newTemp;
        }
}

public  delegate  void  ValueChangedEventHandler(Object  sender,  ValueChangedEventArgs  args);

public  class  ValueChangeObserver
{
        public  ValueChangeObserver(MyValue  t)
        {
                t.ValueChanged  +=  this.ValueChange;
        }

        public  void  ValueChange(Object  sender,  ValueChangedEventArgs  temp)
        {
                Console.WriteLine  ("ChangeObserver:  Old={0},  New={1},  Change={2}",
                        temp.OldValue,  temp.NewValue,
                        temp.NewValue  -  temp.OldValue);
        }
}

public  class  ValueAverageObserver
{
        private  int  sum  =  0,  count  =  0;

        public  ValueAverageObserver(MyValue  t)
        {
                t.ValueChanged  +=  this.ValueChange;
        }

        public  void  ValueChange(Object  sender,  ValueChangedEventArgs  temp)
        {
                count++;
                sum  +=  temp.NewValue;

                Console.WriteLine("AverageObserver:  Average={0:F}",  (double)sum  /  (double)count);
        }
}

public  class  MyValue
{
        private  int  myvalue  =  0;

        public  event  ValueChangedEventHandler  ValueChanged;

        virtual  protected  void  OnValueChanged(ValueChangedEventArgs  args)
        {
                if  (ValueChanged  !=  null)
                {
                        ValueChanged(this,  args);
                }
        }

        public  int  Value
        {
                get  {  return  myvalue;  }

                set
                {
                        ValueChangedEventArgs  args  =  new  ValueChangedEventArgs(myvalue,  value);
                        myvalue  =  value;
                        OnValueChanged(args);
                }
        }
}

public  class  MainClass
{
        public  static  void  Main()
        {
                MyValue  t  =  new  MyValue();

                new  ValueChangeObserver(t);
                new  ValueAverageObserver(t);

                t.Value  =  100;
                t.Value  =  99;
                t.Value  =  88;
                t.Value  =  77;                
        }
}