笔记-大话设计模式-15 抽象工厂模式

抽象工厂模式(Abstract Factory)，提供一个创建一系列相关或相互依赖对象的接口，而无需指定它们具体的类。

所有在用简单工厂的地方，都可以考虑用反射技术来去除switch或if，解除分支判断带来的耦合。

Demo:

    interface IUser
    {
        void Insert(User user);
        User GetUser(int id);
    }

    class User
    {
        private int _id;

        public int Id
        {
            get { return _id; }
            set { _id = value; }
        }

        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }

    }

    class MySqlUser : IUser
    {
        public void Insert(User user)
        {
            Console.WriteLine("MySqlUser的Insert");
        }

        public User GetUser(int id)
        {
            Console.WriteLine("MySqlUser的GetUser");
            return null;
        }
    }

    class SqlServerUser : IUser
    {
        public void Insert(User user)
        {
            Console.WriteLine("SqlserverUser的Insert");
        }

        public User GetUser(int id)
        {
            Console.WriteLine("SqlserverUser的GetUser");
            return null;
        }
    }

Abstract factory type and factory types:

    interface IFactory
    {
        IUser CreateUser();
    }

    class MySqlFactory : IFactory
    {
        public IUser CreateUser()
        {
            return new MySqlUser();
        }
    }

    class SqlServerFactory : IFactory
    {
        public IUser CreateUser()
        {
            return new SqlServerUser();
        }
    }

Test:

            IFactory factory = new MySqlFactory();
            IUser user = factory.CreateUser();
            user.Insert(new User());
            user.GetUser(1);

可以通过反射和配置文件改善抽象工厂模式：

  <appSettings>
    <add key="DB" value="MySql"/>
  </appSettings>

    class DataAccess
    {
        private static readonly string db = ConfigurationManager.AppSettings["DB"];
        private static readonly string assemblyName = "ConsoleApplication1";
        private static readonly string classPrefix = assemblyName + "." + db + "." + db;

        public static IUser CreateUser()
        {
            return (IUser)Assembly.Load(assemblyName).CreateInstance(classPrefix + "User");
            //switch (db)
            //{
            //    case "SqlServer":
            //        //return new SqlserverUser();

            //    case "MySql":
            //        //return new MySqlUser();
            //        return (IUser)Assembly.Load(assemblyName).CreateInstance(classPrefix + "User");
            //    default:
            //        throw new Exception("未实现");
            //}
        }

    }

Test:

            IUser user = DataAccess.CreateUser();
            user.Insert(new User());
            user.GetUser(1);