工廠方法模式:定義一個用於創建對象的接口，讓子類來決定實例化哪一個類。工廠方法使一個類的實例化延遲到子類。

簡單工廠模式的最大有點在於工廠勒種包含了必要的邏輯判斷，根據客戶端的選擇條件動態實例化相關的類，對客戶端來說，去除了與具體產品的依賴。

工廠方法模式實現時，客戶端需要決定實例化哪一個工廠來實現運算類，選擇判斷的問題還是存在的。工廠方法吧簡單工廠的內部邏輯轉移到了客戶端代碼來進行。

/// <summary>
    /// 運算類
    /// </summary>
   public class Operation
    {
        public double
 
 NumA { get; set; }

        public double NumB { get; set; }

        public virtual double GetResult()
        {
            double result = 0;
            return result;
        }
    }

    /// <summary>
    /// 加法類
    /// </summary>
   public class OperationAdd : Operation
    {
        public
 
 override double GetResult()
        {
            double result = 0;
            result = NumA + NumB;
            return result;
        }
    }

    /// <summary>
    /// 減法類
    /// </summary>
    public class OperationSub : Operation
    {
        public override double GetResult()
        {
            
 
double result = 0;
            result = NumA - NumB;
            return result;
        }
    }


    /// <summary>
    /// 工廠接口
    /// </summary>
    public interface IFactory
    {
        Operation FactoryMethod();
    }

    /// <summary>
    /// 加法工廠
    /// </summary>
    public class AddFactory : IFactory
    {
        public Operation FactoryMethod()
        {
            return new OperationAdd();
        }
    }

    /// <summary>
    /// 減法工廠
    /// </summary>
    public class SubFactory : IFactory
    {
        public Operation FactoryMethod()
        {
            return new OperationSub();
        }
    }

   class Program
    {
        static void Main(string[] args)
        {
            IFactory[] fac = new IFactory[2];
            fac[0] = new AddFactory();
            fac[1] = new SubFactory();

            Operation oper;
            oper = fac[0].FactoryMethod();
            oper.NumA=10;
            oper.NumB=5;
            Console.WriteLine("Called By {0}", oper.GetType().Name);
            Console.WriteLine("Result={0}", oper.GetResult().ToString());
         
            oper = fac[1].FactoryMethod();
            oper.NumA = 10;
            oper.NumB = 5;
            Console.WriteLine("Called By {0}", oper.GetType().Name);
            Console.WriteLine("Result={0}", oper.GetResult().ToString());

            Console.ReadKey();
        }
    }

http://www.cnblogs.com/lxblog/p/4119426.html

工廠方法模式（Factory Method）