策略模式(Strategy Pattern)

模式定义

策略模式(Strategy Pattern)：定义一系列算法，将每一个算法封装起来，并让它们可以相互替换。

UML类图

• 环境类(Context)
• 抽象策略类(Strategy)

• 具体策略类(ConcreteStrategy)

  代码结构

  public class StrategyApp
  {
      public void Run()
      {
          Context context;
          context = new Context(new ConcreteStrategyA());
          context.ContextInterface();
  
          context = new Context(new ConcreteStrategyB());
          context.ContextInterface();
      }
  }
  
  abstract class Strategy
  {
      public abstract void AlgorithmInterface();
  }
  
  class ConcreteStrategyA : Strategy
  {
      public override void AlgorithmInterface()
      {
          Console.WriteLine( "Called ConcreteStrategyA.AlgorithmInterface()");
      }
  }
  
  class ConcreteStrategyB : Strategy
  {
      public override void AlgorithmInterface()
      {
          Console.WriteLine("Called ConcreteStrategyB.AlgorithmInterface()");
      }
  }
  
  class Context
  {
      private Strategy _strategy;
  
      public Context(Strategy strategy)
      {
          this._strategy = strategy;
      }
  
      public void ContextInterface()
      {
          _strategy.AlgorithmInterface();
      }
  }

  情景案例

  定义不同的排序算法

  class MainApp
  {
      static void Main()
      {
          SortedList studentRecords = new SortedList();
  
          studentRecords.Add("Samual");
          studentRecords.Add("Jimmy");
          studentRecords.Add("Sandra");
          studentRecords.Add("Vivek");
          studentRecords.Add("Anna");
  
          studentRecords.SetSortStrategy(new QuickSort());
          studentRecords.Sort();
  
          studentRecords.SetSortStrategy(new ShellSort());
          studentRecords.Sort();
  
          Console.ReadKey();
      }
  }
  
  /// <summary>
  /// 抽象算法
  /// </summary>
  abstract class SortStrategy
  {
      public abstract void Sort(List<string> list);
  }
  
  /// <summary>
  /// 快速排序算法
  /// </summary>
  class QuickSort : SortStrategy
  {
      public override void Sort(List<string> list)
      {
          list.Sort(); // Default is Quicksort
  
          Console.WriteLine("QuickSorted list ");
      }
  }
  
  /// <summary>
  /// 插入排序
  /// </summary>
  class ShellSort : SortStrategy
  {
      public override void Sort(List<string> list)
      {
          //list.ShellSort(); not-implemented
          Console.WriteLine("ShellSorted list ");
      }
  }
  
  /// <summary>
  /// 环境类
  /// </summary>
  class SortedList
  {
      private List<string> _list = new List<string>();
      private SortStrategy _sortstrategy;
  
      public void SetSortStrategy(SortStrategy sortstrategy)
      {
          this._sortstrategy = sortstrategy;
      }
  
      public void Add(string name)
      {
          _list.Add(name);
      }
  
      public void Sort()
      {
          _sortstrategy.Sort(_list);
  
          foreach (string name in _list)
          {
              Console.WriteLine(" " + name);
          }
          Console.WriteLine();
      }
  }