Facade.md

Facade

Definition

Provide a unified interface to a set of interfaces in a subsystem. Façade defines a higher-level interface that makes the subsystem easier to use.

Frequency of use:

High

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UML class diagram

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Participants

    The classes and objects participating in this pattern are:

• **Facade **  (MortgageApplication)
  • knows which subsystem classes are responsible for a request.
  • delegates client requests to appropriate subsystem objects.
• **Subsystem classes **  (Bank, Credit, Loan)
  • implement subsystem functionality.
  • handle work assigned by the Facade object.
  • have no knowledge of the facade and keep no reference to it.

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Structural code in C#

This structural code demonstrates the Facade pattern which provides a simplified and uniform interface to a large subsystem of classes.

using System;

namespace DoFactory.GangOfFour.Facade.Structural
{
    /// <summary>
    /// MainApp startup class for Structural
    /// Facade Design Pattern.
    /// </summary>
    class MainApp
    {
        /// <summary>
        /// Entry point into console application.
        /// </summary>
        public static void Main()
        {
            Facade facade = new Facade();

            facade.MethodA();
            facade.MethodB();

            // Wait for user
            Console.ReadKey();
        }
    }

    /// <summary>
    /// The 'Subsystem ClassA' class
    /// </summary>
    class SubSystemOne
    {
        public void MethodOne()
        {
            Console.WriteLine(" SubSystemOne Method");
        }
    }

    /// <summary>
    /// The 'Subsystem ClassB' class
    /// </summary>
    class SubSystemTwo
    {
        public void MethodTwo()
        {
            Console.WriteLine(" SubSystemTwo Method");
        }
    }

    /// <summary>
    /// The 'Subsystem ClassC' class
    /// </summary>
    class SubSystemThree
    {
        public void MethodThree()
        {
            Console.WriteLine(" SubSystemThree Method");
        }
    }

    /// <summary>
    /// The 'Subsystem ClassD' class
    /// </summary>
    class SubSystemFour
    {
        public void MethodFour()
        {
            Console.WriteLine(" SubSystemFour Method");
        }
    }

    /// <summary>
    /// The 'Facade' class
    /// </summary>
    class Facade
    {
        private SubSystemOne _one;
        private SubSystemTwo _two;
        private SubSystemThree _three;
        private SubSystemFour _four;

        public Facade()
        {
            _one = new SubSystemOne();
            _two = new SubSystemTwo();
            _three = new SubSystemThree();
            _four = new SubSystemFour();
        }

        public void MethodA()
        {
            Console.WriteLine("\nMethodA() ---- ");
            _one.MethodOne();
            _two.MethodTwo();
            _four.MethodFour();
        }

        public void MethodB()
        {
            Console.WriteLine("\nMethodB() ---- ");
            _two.MethodTwo();
            _three.MethodThree();
        }
    }
}

Output

MethodA() ----\
SubSystemOne Method\
SubSystemTwo Method\
SubSystemFour Method

MethodB() ----\
SubSystemTwo Method\
SubSystemThree Method