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);
        }
    }
}