Csharp:use Activator.CreateInstance with an Interface?

	///<summary>
	///数据访问工厂
	///生成時間2015-2-13 10:54:34
	///塗聚文(Geovin Du)
    /// (利用工厂模式+反射机制+缓存机制,实现动态创建不同的数据层对象接口)
	///</summary>
	public class AbstractFactory
	{


        protected static string path = ConfigurationManager.AppSettings["WebDAL"]; //"DAL";//生成的DLL文件名

        /// <summary>
        /// 数据库类型
        /// </summary>
        protected static string dalType
        {

            
            get
            {
                if (path.Contains("AccessDAL"))
                {
                    //path = "AcessDAL";                    
                    return "AccessDAL";
                }
                else if (path=="DAL")
                {
                   // path = "DAL";//生成的DLL文件名
                    return "SqlServerDAL";//命名空间名称
                }
                else if (path.Contains("MySQLDAL"))
                {
                    return "MySQLDAL";
                }
                else if (path.Contains("DALSQLite"))
                {
                    //path = "DALSQLite";
                    return "SQLiteDAL";
                }
                else if (path.Contains("PostgreSQLDAL"))
                {
                   // path = "DALPostgreSQL";
                    return "PostgreSQLDAL";
                }
                else if (path.Contains("OracleDAL"))
                {
                    return "OracleDAL";
                }
                else
                {
                    //path = "DAL";
                    return "SqlServerDAL";
                }
            }
        }

        public AbstractFactory()
        { }

		///<summary>
		///分页接口
		/// </summary>
		///<returns></returns>
		public static ISelectPage CreateSelectPage()
		{
			//ISelectPage page = new SelectPage();
			//return page;
            string className = "GeovinDu." + dalType + ".SelectPage";
            return (ISelectPage)Assembly.Load(path).CreateInstance(className); //命名空间名称GeovinDu.SqlServerDAL
            //path = "AcessDAL";//生成的DLL文件名

		}

		///<summary>
		///CompanyBranch接口
		/// </summary>
		///<returns></returns>
        public static ICompanyBranch CreateCompanyBranch(string _databaseprefix, string _sysdatarolefix)
		{
            //ICompanyBranch iCompanyBranch = new CompanyBranchDAL();
            //return iCompanyBranch;
            string className = "GeovinDu." + dalType + ".CompanyBranchDAL";//(_databaseprefix, _sysdatarolefix)
            return (ICompanyBranch)Assembly.Load(path).CreateInstance(className); //GeovinDu.SqlServerDAL
		}

		///<summary>
		///EnterpriseType接口
		/// </summary>
		///<returns></returns>
        public static IEnterpriseType CreateEnterpriseType(string _databaseprefix, string _sysdatarolefix)
		{
            //IEnterpriseType iEnterpriseType = new EnterpriseTypeDAL();
            //return iEnterpriseType;
            string className = "GeovinDu." + dalType + ".EnterpriseTypeDAL";
            return (IEnterpriseType)Assembly.Load(path).CreateInstance(className); 
		}

		///<summary>
		///LoginDiaryList接口
		/// </summary>
		///<returns></returns>
        public static ILoginDiaryList CreateLoginDiaryList(string _databaseprefix, string _sysdatarolefix)
		{
			//ILoginDiaryList iLoginDiaryList = new LoginDiaryListDAL();
			//return iLoginDiaryList;
            string className = "GeovinDu." + dalType + ".LoginDiaryListDAL";//(_databaseprefix, _sysdatarolefix)
            return (ILoginDiaryList)Assembly.Load(path).CreateInstance(className); 
		}

		///<summary>
		///OperatingUser接口
        ///https://msdn.microsoft.com/zh-cn/library/ms173128(VS.80).aspx   
        ///https://*.com/questions/2202381/reflection-how-to-invoke-method-with-parameters
		/// </summary>
		///<returns></returns>
        public static IOperatingUser CreateOperatingUser(string _databaseprefix, string _sysdatarolefix)
		{
            //IOperatingUser iOperatingUser = new OperatingUserDAL(_databaseprefix, _sysdatarolefix);
			//return iOperatingUser;
            IOperatingUser iOperatingUser = null;
            string className = "GeovinDu." + dalType + ".OperatingUserDAL";//(_databaseprefix, _sysdatarolefix)
            //return (IOperatingUser)Assembly.Load(path).CreateInstance(className); 

            //string className = "GeovinDu.SQLiteDAL.OperatingUserDAL";
            //Assembly assembly = Assembly.LoadFrom(@"G:\winxp备份\PayrollPrint4\PayrollPrint\bin\Release\DALSQLite.dll");
            // object oo = assembly.CreateInstance(className);  //得到对象命名空间名
            // MethodInfo methodinfo = assembly.GetType("GeovinDu.GeovinDu.SQLiteDAL.OperatingUserDAL").GetMethod("OperatingUserDAL");   //得到方法
            //Object obj = methodinfo.Invoke(oo, new object[] { _databaseprefix, _sysdatarolefix });
            //IOperatingUser iOperatingUser = (IOperatingUser)obj;
            object obj = Assembly.Load(path).CreateInstance(className);
            Type t2 = obj.GetType();// Type.GetType("GeovinDu.SQLiteDAL.OperatingUserDAL", false, true);
            if (t2 != null)
            {
                iOperatingUser = (OperatingUserDAL)Activator.CreateInstance(t2, new object[] { });          //Assembly.Load(path).CreateInstance(className);  //值為空
            }

             //iOperatingUser = (IOperatingUser)Activator.CreateInstance(System.Type.GetType(className));


            return iOperatingUser;

		}

        ///<summary>
        ///PrintWordDocumentTemplateList接口
        /// </summary>
        ///<returns></returns>
        public static IPrintWordDocumentTemplateList CreatePrintWordDocumentTemplateList(string _databaseprefix, string _sysdatarolefix)
        {
            //IPrintWordDocumentTemplateList iPrintWordDocumentTemplateList = new PrintWordDocumentTemplateListDAL();
            //return iPrintWordDocumentTemplateList;
            string className = "GeovinDu." + dalType + ".PrintWordDocumentTemplateListDAL";//(_databaseprefix, _sysdatarolefix)
            return (IPrintWordDocumentTemplateList)Assembly.Load(path).CreateInstance(className); 
        }
       
        /// <summary>
        /// 
        /// </summary>
        /// <returns></returns>
        public static ISysConfig CreateSysConfig()
        {

            string className = "GeovinDu." + dalType + ".SysConfigDAL";
            return (ISysConfig)Assembly.Load(path).CreateInstance(className); 
            //databaseprefix = _databaseprefix;
            //ISysConfig iSysConfig = new DAL.SysConfigDAL();
            //return iSysConfig;
        }
	}

　　

https://github.com/fabriciorissetto/CustomActivator

https://www.codeproject.com/Articles/55710/Reflection-in-NET