1.簡單工廠模式

原理

這種類型的設計模式屬於創建型模式，它提供了一種創建對象的最佳方式。
在工廠模式中，我們在創建對象時不會對客戶端暴露創建邏輯，並且是通過使用一個共同的接口來指向新創建的對象。

意圖

定義一個創建對象的接口，讓其子類自己決定實例化哪一個工廠類，工廠模式使其創建過程延遲到子類進行。

主要解決

主要解決接口選擇的問題。

代碼

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace 簡單工廠模式
{
    class Program
    {
        static void Main(string[] args)
        {
            Operation oper;
            oper = OperationFactory.createOperate("+");
            oper.NumberA = 1;
            oper.NumberB = 2;
            double result = oper.GetResult();
            Console.Write("result: " + result);
            Console.ReadKey();
        }
    }
}

Operation.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace 簡單工廠模式
{
    //簡單工廠類
    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;
            }
            return oper;
        }
    }

    //運算類
    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;
        }
    }
    //加法類
    class OperationAdd : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA + NumberB;
            return result;
        }
    }
    //減法類
    class OperationSub : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA - NumberB;
            return result;
        }
    }
    //乘法類
    class OperationMul : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA * NumberB;
            return result;
        }
    }
    //除法類
    class OperationDiv : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            if (NumberB == 0) {
                throw new Exception("除數不能爲0."); 
            }
            result = NumberA / NumberB;
            return result;
        }
    }

}

參考

參考書籍：《大話設計模式》
參考鏈接： 菜鳥教程.