C#反射—解決類的實例化問題

利用簡單工廠模式來改進抽象工廠使用的複雜性（抽象工廠詳見 設計模式之—抽象工廠模式）

數據表（User）業務處理接口（IUser）

namespace FactoryMethodPatternDB.CLASS
{
    interface IUser
    {
        void Insert(User user);
        void GetUser(string id);
    }
}

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數據表（Department）業務處理接口（IDepartment）

namespace FactoryMethodPatternDB.CLASS
{
    interface IDepartment
    {
        void Insert(Department dept);
        void GetDept(string id);
    }
}

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SQL操做表（User）類（SqlServerUser）

namespace FactoryMethodPatternDB.CLASS
{
    class SqlServerUser:IUser
    {
        public void Insert(User user)
        {
            Console.WriteLine("在User表中插入一條數據{0}！SQL數據庫",user);
        }

        public void GetUser(string id)
        {
            Console.WriteLine("經過{0}來查找數據！SQL數據庫", id);
        }
    }
}

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SQL操做表（Department）類（SqlServerDepartment）

namespace FactoryMethodPatternDB.CLASS
{
    class SqlServerDepartment:IDepartment
    {
        public void Insert(Department dept)
        {
            Console.WriteLine("在{0}表中插入數據！SQL數據庫", dept);
        }
        public void GetDept(string id)
        {
            Console.WriteLine("經過{0}查找數據庫表！SQL數據庫", id);
        }

    }
}

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ACCESS操做表（User）類（AccessUser）

namespace FactoryMethodPatternDB.CLASS
{
    class AccessUser:IUser
    {
        public void Insert(User user)
        {
            Console.WriteLine("在{0}表中插入數據！Access數據庫",user);
        }
        public void GetUser(string id)
        {
            Console.WriteLine("經過{0}查找數據庫表！Access數據庫",id);
        }
    }
}

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ACCESS操做表（Department）類（AccessDepartment）

namespace FactoryMethodPatternDB.CLASS
{
    class AccessDepartment:IDepartment
    {
        public void Insert(Department dept)
        {
            Console.WriteLine("在{0}表中插入數據！Access數據庫", dept);
        }
        public void GetDept(string id)
        {
            Console.WriteLine("經過{0}查找數據庫表！Access數據庫", id);
        }
    }
}

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工廠接口和工廠類被SelectDB替換：

namespace FactoryMethodPatternDB
{
    class SelectDB
    {
        //private static readonly string db = "Sqlserver";
        private static readonly string db = "Access";
        public static IUser CreateUser()
        {
            IUser iuser = null;
            switch (db)
            {
                case "Sqlserver":
                    iuser = new SqlServerUser();
                    break;
                case "Access":
                    iuser = new AccessUser();
                    break;
            }
            return iuser;
        }

        public static IDepartment CreateDept()
        {
            IDepartment idept = null;
            switch (db)
            {
                case "Sqlserver":
                    idept = new SqlServerDepartment();
                    break;
                case "Access":
                    idept = new AccessDepartment();
                    break;
            }
            return idept;
        }
    }
}

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簡單工廠模式測試類

      //簡單工廠與抽象工廠模式相結合
          User user = new User();
            Department dept = new Department();
            IUser iuser = SelectDB.CreateUser();
            iuser.Insert(user);
            iuser.GetUser("ID");
            IDepartment idept = SelectDB.CreateDept();
            idept.Insert(dept);
            idept.GetDept("name");

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若增長Oracle數據庫，則須要更改Switch語句塊 違背開放-封閉原則。解決此問題的方法是採用反射

將SelectDB換成反射類（Reflection）

添加反射引用命名空間using System.Reflection;

using System.Reflection;
namespace FactoryMethodPatternDB
{
    class Reflection
    {
        private static readonly string AssemblyName = "FactoryMethodPatternDB"; //程序集
        private static readonly string db = "SqlServer";  //業務類的名稱爲SqlServer + 表名 如（SqlServerUser）方便反射使用

        public static IUser CreateUser()
        {
            string className = AssemblyName + ".CLASS." + db  + "User"; //類名（帶命名空間）
            return (IUser)Assembly.Load(AssemblyName).CreateInstance(className);
        }

        public static IDepartment CreateDept()
        {
            string className = AssemblyName + "." + "Department";
            return (IDepartment)Assembly.Load(AssemblyName).CreateInstance(className);
        }
    }
}

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 反射測試類

   //反射與抽象工廠模式相結合
          User user = new User();
            Department dept = new Department();
            IUser iuser = Reflection.CreateUser();
            iuser.Insert(user);
            iuser.GetUser("ID");

            IDepartment idept = Reflection.CreateDept();
            idept.Insert(dept);
            idept.GetDept("Name");

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