设计模式（二）简单工厂模式和工厂方法模式

简单工厂模式

• 用来管理创造实例，解决对象创建
  通过子类自动向上转型为父类的特性，可以通过父类控制不同子类，调用相应子类的实现方法来实现不同的操作。
  

// 操作类
public class Operation
    {
        private double _numberA = 0;
        private double _numberB = 0;

        public double NumberA {
            get { return _numberA; }
            set { _numberA = value; }
        }

        public double NumberB {
            get { return _numberB; }
            set { _numberB = value; }
        }

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

 // 具体操作类：操作类
 class OperationAdd : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA + NumberB;
            return result;
        }
    }

// 工厂类，用来控制创造操作实例
public class OperationFactory
    {
        public static Operation CreateOperate (string operate)
        {
            Operation oper = null;
            switch (operate)
            {
                case "+":
                    oper = new OperationAdd();
                    break;
                case "-":
                    oper = new OperationSub();
                    break;
                case "*":
                    oper = new OperationMul();
                    break;
                case "/":
                    oper = new OperationDiv();
                    break;
                default:
                    throw new Exception("请输入正确的运算符！");

            }
       
            return oper;

        }
    }

    Console.Write("请输入数字A：");
    string strNumberA = Console.ReadLine();
    Console.Write("请输入运算符（+、-、*、/）：");
    string strOperate = Console.ReadLine();
    Console.Write("请输入数字B：");
    string strNumberB = Console.ReadLine();

    Operation oper = OperationFactory.CreateOperate(strOperate);
    oper.NumberA = Convert.ToDouble(strNumberA);
    oper.NumberB = Convert.ToDouble(strNumberB);
    double result = oper.GetResult();
    Console.WriteLine(oper.NumberA + strOperate  + oper.NumberB + "=" + result);
    Console.ReadLine();

工厂方法模式

因为简单工厂模式违背了开放-封闭原则。不但开放了扩展（新增操作类），还开放了修改（工厂类）因此需要使用工厂方法模式封闭修改。
对于工厂类，抽象出来接口，用来创建对应产品的方法，将原来修改工厂类，该为了增加对应的工厂类。

//  抽象接口
public interface IFactory
{
    public Operation CreateOperation();
}
// 工厂
public class AddFactory : IFactory
{
    public Operation CreateOperation()
    {
        return new OperationAdd();
    }
}

    Console.Write("请输入数字A：");
    string strNumberA = Console.ReadLine();
    Console.Write("请输入数字B：");
    string strNumberB = Console.ReadLine();

    IFactory factory = new AddFatory();
    Operation oper = factory.CreateOperation();
    oper.NumberA = Convert.ToDouble(strNumberA);
    oper.NumberB = Convert.ToDouble(strNumberB);
    double result = oper.GetResult();