.NET Design Patterns(4) - Prototype

Prototype Design Pattern

definition  UML diagram  participants

sample code in C#

definition Specify the kind of objects to create using a prototypical instance, and create new objects by copying this prototype. Frequency of use:   medium

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UML class diagram

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participants

    The classes and/or objects participating in this pattern are:

• Prototype  (ColorPrototype)
  • declares an interface for cloning itself
• ConcretePrototype  (Color)
  • implements an operation for cloning itself
• Client  (ColorManager)
  • creates a new object by asking a prototype to clone itself

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sample code in C#

This structural code demonstrates the Prototype pattern in which new objects are created by copying pre-existing objects (prototypes) of the same class.

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// Prototype pattern -- Structural example

using System; namespace DoFactory.GangOfFour.Prototype.Structural {   /// <summary>   /// MainApp startup class for Structural   /// Prototype Design Pattern.   /// </summary>   class MainApp   {     /// <summary>     /// Entry point into console application.     /// </summary>     static void Main()     {       // Create two instances and clone each       ConcretePrototype1 p1 = new ConcretePrototype1("I");       ConcretePrototype1 c1 = (ConcretePrototype1)p1.Clone();       Console.WriteLine("Cloned: {0}", c1.Id);       ConcretePrototype2 p2 = new ConcretePrototype2("II");       ConcretePrototype2 c2 = (ConcretePrototype2)p2.Clone();       Console.WriteLine("Cloned: {0}", c2.Id);       // Wait for user       Console.ReadKey();     }   }   /// <summary>   /// The 'Prototype' abstract class   /// </summary>   abstract class Prototype   {     private string _id;     // Constructor     public Prototype(string id)     {       this._id = id;     }     // Gets id     public string Id     {       get { return _id; }     }     public abstract Prototype Clone();   }   /// <summary>   /// A 'ConcretePrototype' class   /// </summary>   class ConcretePrototype1 : Prototype   {     // Constructor     public ConcretePrototype1(string id)       : base(id)     {     }     // Returns a shallow copy     public override Prototype Clone()     {       return (Prototype)this.MemberwiseClone();     }   }   /// <summary>   /// A 'ConcretePrototype' class   /// </summary>   class ConcretePrototype2 : Prototype   {     // Constructor     public ConcretePrototype2(string id)       : base(id)     {     }     // Returns a shallow copy     public override Prototype Clone()     {       return (Prototype)this.MemberwiseClone();     }   } }

Output Cloned: I Cloned: II

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This real-world code demonstrates the Prototype pattern in which new Color objects are created by copying pre-existing, user-defined Colors of the same type.

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// Prototype pattern -- Real World example

using System; using System.Collections.Generic; namespace DoFactory.GangOfFour.Prototype.RealWorld {   /// <summary>   /// MainApp startup class for Real-World   /// Prototype Design Pattern.   /// </summary>   class MainApp   {     /// <summary>     /// Entry point into console application.     /// </summary>     static void Main()     {       ColorManager colormanager = new ColorManager();       // Initialize with standard colors       colormanager["red"] = new Color(255, 0, 0);       colormanager["green"] = new Color(0, 255, 0);       colormanager["blue"] = new Color(0, 0, 255);       // User adds personalized colors       colormanager["angry"] = new Color(255, 54, 0);       colormanager["peace"] = new Color(128, 211, 128);       colormanager["flame"] = new Color(211, 34, 20);       // User clones selected colors       Color color1 = colormanager["red"].Clone() as Color;       Color color2 = colormanager["peace"].Clone() as Color;       Color color3 = colormanager["flame"].Clone() as Color;       // Wait for user       Console.ReadKey();     }   }   /// <summary>   /// The 'Prototype' abstract class   /// </summary>   abstract class ColorPrototype   {     public abstract ColorPrototype Clone();   }   /// <summary>   /// The 'ConcretePrototype' class   /// </summary>   class Color : ColorPrototype   {     private int _red;     private int _green;     private int _blue;     // Constructor     public Color(int red, int green, int blue)     {       this._red = red;       this._green = green;       this._blue = blue;     }     // Create a shallow copy     public override ColorPrototype Clone()     {       Console.WriteLine(         "Cloning color RGB: {0,3},{1,3},{2,3}",         _red, _green, _blue);       return this.MemberwiseClone() as ColorPrototype;     }   }   /// <summary>   /// Prototype manager   /// </summary>   class ColorManager   {     private Dictionary<string, ColorPrototype> _colors =       new Dictionary<string, ColorPrototype>();     // Indexer     public ColorPrototype this[string key]     {       get { return _colors[key]; }       set { _colors.Add(key, value); }     }   } }

Output Cloning color RGB: 255,  0,  0 Cloning color RGB: 128,211,128 Cloning color RGB: 211, 34, 20

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This .NET optimized code demonstrates the same real-world situation as above but uses modern, built-in .NET features, such as, generics, reflection, object initializers, automatic properties, etc.