策略模式之C#版本（原创翻译版本）

Definition Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

UML class diagram

Participants

The classes and/or objects participating in this pattern are: Strategy  (SortStrategy) declares an interface common to all supported algorithms. Context uses this interface to call the algorithm defined by a ConcreteStrategy ConcreteStrategy  (QuickSort, ShellSort, MergeSort) implements the algorithm using the Strategy interface Context  (SortedList) is configured with a ConcreteStrategy object maintains a reference to a Strategy object may define an interface that lets Strategy access its data.

Sample code in C#

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This structural code demonstrates the Strategy pattern which encapsulates functionality in the form of an object. This allows clients to dynamically change algorithmic strategies. // Strategy pattern -- Structural example using System; // "Strategy" abstract class Strategy {   // Methods   abstract public void AlgorithmInterface(); } // "ConcreteStrategyA" class ConcreteStrategyA : Strategy {   // Methods   override public void AlgorithmInterface()   {   Console.WriteLine(       "Called ConcreteStrategyA.AlgorithmInterface()");   } } // "ConcreteStrategyB" class ConcreteStrategyB : Strategy {   // Methods   override public void AlgorithmInterface()   {     Console.WriteLine(         "Called ConcreteStrategyB.AlgorithmInterface()");   } } // "ConcreteStrategyC" class ConcreteStrategyC : Strategy {   // Methods   override public void AlgorithmInterface()   {     Console.WriteLine(         "Called ConcreteStrategyC.AlgorithmInterface()");   } } // "Context" class Context {   // Fields   Strategy strategy;   // Constructors   public Context( Strategy strategy )   {     this.strategy = strategy;   }   // Methods   public void ContextInterface()   {     strategy.AlgorithmInterface();   } } /// <summary> /// Client test /// </summary> public class Client {   public static void Main( string[] args )   {     // Three contexts following different strategies     Context c = new Context( new ConcreteStrategyA() );     c.ContextInterface();     Context d = new Context( new ConcreteStrategyB() );     d.ContextInterface();     Context e = new Context( new ConcreteStrategyC() );      e.ContextInterface();   } } Output Called ConcreteStrategyA.AlgorithmInterface() Called ConcreteStrategyB.AlgorithmInterface() Called ConcreteStrategyC.AlgorithmInterface() This real-world code demonstrates the Strategy pattern which encapsulates sorting algorithms in the form of sorting objects. This allows clients to dynamically change sorting strategies including Quicksort, Shellsort, and Mergesort. // Strategy pattern -- Real World example using System; using System.Collections; // "Strategy" abstract class SortStrategy {   // Methods   abstract public void Sort( ArrayList list ); } // "ConcreteStrategy" class QuickSort : SortStrategy {   // Methods   public override void Sort(ArrayList list )   {     list.Sort(); // Default is Quicksort     Console.WriteLine("QuickSorted list ");   } } // "ConcreteStrategy" class ShellSort : SortStrategy {   // Methods   public override void Sort(ArrayList list )   {     //list.ShellSort();     Console.WriteLine("ShellSorted list ");   } } // "ConcreteStrategy" class MergeSort : SortStrategy {   // Methods   public override void Sort( ArrayList list )   {     //list.MergeSort();     Console.WriteLine("MergeSorted list ");   } } // "Context" class SortedList {   // Fields   private ArrayList list = new ArrayList();   private SortStrategy sortstrategy;   // Constructors   public void SetSortStrategy( SortStrategy sortstrategy )   {     this.sortstrategy = sortstrategy;   }   // Methods   public void Sort()   {     sortstrategy.Sort( list );   }   public void Add( string name )   {     list.Add( name );   }   public void Display()   {     foreach( string name in list )       Console.WriteLine( " " + name );   } } /// <summary> /// StrategyApp test /// </summary> public class StrategyApp {   public static void Main( string[] args )   {     // Two contexts following different strategies     SortedList studentRecords = new SortedList( );     studentRecords.Add( "Samual" );     studentRecords.Add( "Jimmy" );     studentRecords.Add( "Sandra" );     studentRecords.Add( "Anna" );     studentRecords.Add( "Vivek" );     studentRecords.SetSortStrategy( new QuickSort() );     studentRecords.Sort();     studentRecords.Display();   } } Output QuickSorted list  Anna  Jimmy  Samual  Sandra  Vivek