Implement the Observer Pattern - CSharp Design Patterns

CSharp examples for Design Patterns:Observer Pattern

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Description

Implement the Observer Pattern

Demo Code


using System;/*w  w w . j a v a 2 s. com*/

    public class ValueChangedEventArgs : EventArgs
    {
        private readonly int oldValue, newValue;
        public ValueChangedEventArgs(int oldTemp, int newTemp)
        {
            oldValue = oldTemp;
            newValue = newTemp;
        }

        public int OldValue { get { return oldValue; } }
        public int NewValue { get { return newValue; } }
    }

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

    public class ValueChangeObserver
    {
        public ValueChangeObserver(Thermostat 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(Thermostat 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 Thermostat
    {
        private int temperature = 0;
        public event ValueChangedEventHandler ValueChanged;
        virtual protected void OnValueChanged(ValueChangedEventArgs args)
        {
            if (ValueChanged != null)
            {
                ValueChanged(this, args);
            }
        }
        public int Value
        {
            get { return temperature; }

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

class MainClass
    {
        public static void Main()
        {
            Thermostat t = new Thermostat();
            new ValueChangeObserver(t);
            new ValueAverageObserver(t);
            do
            {
                Console.WriteLine(Environment.NewLine);
                Console.Write("Enter current temperature: ");

                try
                {
                    t.Value = Int32.Parse(Console.ReadLine());
                }
                catch (Exception)
                {
                    Console.WriteLine("Terminating Observer Pattern Example.");
                    return;
                }
            } while (true);
        }
    }

Result


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