003-单例OR工厂模式

单例模式：DbContextFactory.cs

 using CZBK.ItcastOA.Model;
 using System;
 using System.Collections.Generic;
 using System.Data.Entity;
 using System.Linq;
 using System.Runtime.Remoting.Messaging;
 using System.Text;
 using System.Threading.Tasks;

 namespace CZBK.ItcastOA.DAL
 {
     public class DbContextFactory
     {
         /// <summary>
         /// 保证EF上下文实例线程内唯一.
         /// </summary>
         /// <returns></returns>
         public static DbContext CreateDbContext()
         {
             DbContext dbContext = (DbContext)CallContext.GetData("db");
             if (dbContext == null)
             {
                 dbContext = new OAEntities();
                 CallContext.SetData("db", dbContext);
             }
             return dbContext;
         }
     }
 }

 public class Singleton
 {
     private static Singleton _instance = null;
     private Singleton(){}
     public static Singleton CreateInstance()
     {
         if(_instance == null)
         {
             _instance = new Singleton();
         }
         return _instance;
     }
 }

工厂模式：SimpleFactory.cs

 using CZBK.Shop.IDal;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;

 namespace CZBK.Shop.DalFactory
 {
     /// <summary>
     /// 工厂模式:解决的就是对象的创建（将对象的创建封装起来）
     /// </summary>
     public class SimpleFactory
     {
         public static IUserInfoDal CreateUserInfoDal()
         {
             return new SqlServerDal.UserInfoDal();
         }
     }
 }

抽象工厂模式：AbstractFactory.cs

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

 namespace CZBK.Shop.DalFactory
 {
     /// <summary>
     /// 抽象工厂：本质上与工厂是一样的，都是负责创建对象，但是创建的方式不一样。
     /// </summary>
     public class AbstractFactory
     {
         private static readonly string DalAssembly = ConfigurationManager.AppSettings["DalAssembly"];
         private static readonly string DalNameSpace = ConfigurationManager.AppSettings["DalNameSpace"];
         public static IDal.IUserInfoDal CreateUserInfoDal()
         {
             //通过反射的形式来创建.
             string fullClassName = DalNameSpace + ".UserInfoDal";
             return CreateInstance(fullClassName) as IDal.IUserInfoDal;
         }
         private static object CreateInstance(string fullClassName)
         {
             var assmebly = Assembly.Load(DalAssembly);//加载程序集.
             return assmebly.CreateInstance(fullClassName);
         }
     }
 }