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) 依赖策略类,在解决某个问题时可以通过传入的参数采用不同的策略;
- 抽象策略类(Strategy) 声明所支持算法的抽象方法。
- 具体策略类(ConcreteStrategy) 抽象策略类的子类,实现了在抽象策略类中定义的算法。
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();
}
}