C# 策略模式（Strategy Pattern）

策略模式定义了一系列的算法，并将每一个算法封装起来，使它们可以相互替换。策略模式让算法的变化独立于使用算法的客户。

// 策略接口  
public interface IStrategy  
{  
    void Execute();  
}  
  
// 具体策略A  
public class ConcreteStrategyA : IStrategy  
{  
    public void Execute()  
    {  
        Console.WriteLine("Executing strategy A");  
    }  
}  
  
// 具体策略B  
public class ConcreteStrategyB : IStrategy  
{  
    public void Execute()  
    {  
        Console.WriteLine("Executing strategy B");  
    }  
}  
  
// 上下文类，接收客户的请求并使用某种策略  
public class Context  
{  
    private IStrategy _strategy;  
  
    public Context(IStrategy strategy)  
    {  
        _strategy = strategy;  
    }  
  
    public void SetStrategy(IStrategy strategy)  
    {  
        _strategy = strategy;  
    }  
  
    public void ExecuteStrategy()  
    {  
        _strategy.Execute();  
    }  
}  
  
// 客户端代码  
class Program  
{  
    static void Main(string[] args)  
    {  
        Context context = new Context(new ConcreteStrategyA());  
        context.ExecuteStrategy();  
  
        context.SetStrategy(new ConcreteStrategyB());  
        context.ExecuteStrategy();  
    }  
}