Design Mode (10) Appearance Mode

Mode Introduction

The idea of appearance mode is to hide the complexity of the system.

Example

It is assumed that the kitchen of a restaurant is divided into three parts: the area where cold and hot food and drinks are placed respectively. But you don't care about it as a customer. However, the waiter knows this.

Customer

/// <summary>/// Patron of the restaurant (duh!)/// </summary>class Patron{    private string _name;    public Patron(string name)    {        this._name = name;    }    public string Name    {        get { return _name; }    }}

Declare the interface and order class of the kitchen area

/// <summary>/// All items sold in the restaurant must inherit from this./// </summary>class FoodItem { public int DishID; }/// <summary>/// Each section of the kitchen must implement this interface./// </summary>interface KitchenSection{    FoodItem PrepDish(int DishID);}/// <summary>/// Orders placed by Patrons./// </summary>class Order{    public FoodItem Appetizer { get; set; }    public FoodItem Entree { get; set; }    public FoodItem Drink { get; set; }}

Three areas of the kitchen

/// <summary>/// A division of the kitchen./// </summary>class ColdPrep : KitchenSection{    public FoodItem PrepDish(int dishID)    {        //Go prep the cold item        return new FoodItem()        {            DishID = dishID        };    }}/// <summary>/// A division of the kitchen./// </summary>class HotPrep : KitchenSection{    public FoodItem PrepDish(int dishID)    {        //Go prep the hot entree        return new FoodItem()        {            DishID = dishID        };    }}/// <summary>/// A division of the kitchen./// </summary>class Bar : KitchenSection{    public FoodItem PrepDish(int dishID)    {        //Go mix the drink        return new FoodItem()        {            DishID = dishID        };    }}

Attendant

/// <summary>/// The actual "Facade" class, which hides the complexity of the KitchenSection classes./// After all, there‘s no reason a patron should order each part of their meal individually./// </summary>class Server{    private ColdPrep _coldPrep = new ColdPrep();    private Bar _bar = new Bar();    private HotPrep _hotPrep = new HotPrep();    public Order PlaceOrder(Patron patron, int coldAppID, int hotEntreeID, int drinkID)    {        Console.WriteLine("{0} places order for cold app #" + coldAppID.ToString()                            + ", hot entree #" + hotEntreeID.ToString()                            + ", and drink #" + drinkID.ToString() + ".");        Order order = new Order();        order.Appetizer = _coldPrep.PrepDish(coldAppID);        order.Entree = _hotPrep.PrepDish(hotEntreeID);        order.Drink = _bar.PrepDish(drinkID);        return order;    }}

Client call

static void Main(string[] args){    Server server = new Server();    Console.WriteLine("Hello!  I‘ll be your server today. What is your name?");    var name = Console.ReadLine();    Patron patron = new Patron(name);    Console.WriteLine("Hello " + patron.Name + ". What appetizer would you like? (1-15):");    var appID = int.Parse(Console.ReadLine());    Console.WriteLine("That‘s a good one.  What entree would you like? (1-20):");    var entreeID = int.Parse(Console.ReadLine());    Console.WriteLine("A great choice!  Finally, what drink would you like? (1-60):");    var drinkID = int.Parse(Console.ReadLine());    Console.WriteLine("I‘ll get that order in right away.");    server.PlaceOrder(patron, appID, entreeID, drinkID);  //Here‘s what the Facade simplifies    Console.ReadKey();}

We can see that the customer and the waiter interact.

Summary

The appearance mode is a simple coverage of Complex Systems and is widely used.

Source code

Https://github.com/exceptionnotfound/DesignPatterns/tree/master/Facade

Original

Https://www.exceptionnotfound.net/the-daily-design-pattern-facade/

Design Mode (10) Appearance Mode