1.创建接口

using System;
using System.Collections.Generic;
using System.Text;

namespace zhazha.DB.Interface
{
    public  interface IDBHelper
    {
        void Query();
    }
}

2.实现接口-》类库的方式

using System;
using zhazha.DB.Interface;

namespace zhazha.DB.MySql
{
    public class MySqlHelper : IDBHelper
    {
        public MySqlHelper()
        {
            Console.WriteLine("MySqlHelper被构造");
        }
        public void Query()
        {
            Console.WriteLine("MySqlHelpe被实现了");
        }
    }
}



using System;
using zhazha.DB.Interface;

namespace zhazha.DB.SqlServer
{
    public class SqlServerHelper : IDBHelper
    {
        public SqlServerHelper()
        {
            Console.WriteLine("SqlServer被构造");
        }
        public void Query()
        {
            Console.WriteLine("SqlServer被实现了");
        }
    }
}

3.工厂的创建

load是对应直接exe文件夹下的dll的名字，不用后缀~！其他的load方法不推荐有依赖的问题

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

namespace 发射
{
    public class Factory
    {
        private static string IDBHelperConfig = ConfigurationManager.AppSettings["IDBHelperConfig"];
        private static string DllName = IDBHelperConfig.Split(',')[0];
        private static string TypeName = IDBHelperConfig.Split(',')[1];

        //如果上面的static有错 构造都进不去！！会直接异常

        public static IDBHelper CreateHelper()
        {
            Assembly assembly = Assembly.Load(DllName);  //加载dll
            Type type = assembly.GetType(TypeName);      //获取类型幸喜
            IDBHelper dBHelper = (IDBHelper)Activator.CreateInstance(type);  //创建对象 +强制转换 
            return dBHelper ?? null;

        }
    }
}

注意app的配置文也做了相应的修改

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1"/>
    </startup>
  <appSettings>
    <add key="IDBHelperConfig" value="zhazha.DB.MySql,zhazha.DB.MySql.MySqlHelper"/>
  </appSettings>
</configuration>

4.用工厂创建对象实例

class Program
    {
        static void Main(string[] args)
        {
            Assembly assembly = Assembly.Load("zhazha.DB.MySql");   //加载dll
            Type type = assembly.GetType("zhazha.DB.MySql.MySqlHelper");         //lei
            IDBHelper dBHelper = (IDBHelper)Activator.CreateInstance(type);  //创建实例
            dBHelper.Query();

            Assembly assembly2 = Assembly.Load("zhazha.DB.SqlServer");   //加载dll
            Type type2 = assembly2.GetType("zhazha.DB.SqlServer.SqlServerHelper");         //lei
            IDBHelper dBHelper2 = (IDBHelper)Activator.CreateInstance(type2);  //创建实例
            dBHelper2.Query();


            //------------Reflaction+Factory+Config-------------
            IDBHelper dBHelper1= Factory.CreateHelper();
            dBHelper1.Query();    //可配置 可扩展 反射动态 依照字符串

            Console.ReadLine();
        }
    }