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Facade Pattern provides a unified interface to a set of interfaces in a subsystem. It defines a higher-level interface that makes the subsystem easier to use.

E.g.

I have a Call Details Record (CDR) to be processed by different systems. It is defined in the CDR class

using System;
using System.Collections.Generic;
using System.Text;

namespace FacadePattern
{
    class CDR
    {
        private string aNo;
        private string bNo;
        private double chargedPrice;
        private string imsi;
        private string imei;

        public CDR(string aNo, string bNo,
            double chargedPrice,
            string imsi, string imei)
        {
            this.aNo = aNo;
            this.bNo = bNo;
            this.chargedPrice = chargedPrice;
            this.imsi = imsi;
            this.imei = imei;
        }

        public string ANo
        {
            get
            {
                return this.aNo;
            }
            set
            {
                this.aNo = value;
            }
        }

        public string BNo
        {
            get
            {
                return this.bNo;
            }
            set
            {
                this.bNo = value;
            }
        }

        public double ChargedPrice
        {
            get
            {
                return this.chargedPrice;
            }
            set
            {
                this.chargedPrice = value;
            }
        }

        public string IMSI
        {
            get
            {
                return this.imsi;
            }
            set
            {
                this.imsi = value;
            }
        }

        public string IMEI
        {
            get
            {
                return this.imei;
            }
            set
            {
                this.imei = value;
            }
        }

    }
}

The subsystems are RatingEngine and BillingSystem.

using System;
using System.Collections.Generic;
using System.Text;

namespace FacadePattern
{
    class RatingEngine
    {
        public bool Rate(CDR cdr)
        {
            Console.WriteLine("Rate the CDR.");
            return true;
        }
    }
}

using System;
using System.Collections.Generic;
using System.Text;

namespace FacadePattern
{
    class BillingSystem
    {
        public bool Bill(CDR cdr)
        {
            Console.WriteLine("Bill the CDR.");
            return true;
        }
    }
}

CDRProcessor calls the subsystems to process the CDR.

using System;
using System.Collections.Generic;
using System.Text;

namespace FacadePattern
{
    class CDRProcessor
    {
        private RatingEngine ratingEngine;
        private BillingSystem billingSystem;

        public CDRProcessor()
        {
            ratingEngine = new RatingEngine();
            billingSystem = new BillingSystem();
        }

        public bool Process(CDR cdr)
        {
            Console.WriteLine("Process the CDR.");
            return (ratingEngine.Rate(cdr) &&
                      billingSystem.Bill(cdr));
        }
    }
}

To test it,

using System;
using System.Collections.Generic;
using System.Text;

namespace FacadePattern
{
    class Program
    {
        static void Main(string[] args)
        {
            CDR cdr = new CDR("123", "456",
                1.5, "12121212121", "1223232323");

            CDRProcessor cdrProcessor  = new CDRProcessor();
            bool isProcessed = cdrProcessor.Process(cdr);

            Console.Read();
        }
    }
}

The output

Process the CDR.
Rate the CDR.
Bill the CDR.