项目文件中含有两个config文件，app.config与app1.config，如何获取app1.config中的配置

想要通过配置文件配置C#前台画面，好奇做了以下测试：在项目中新建了app.config与app1.config两个配置文件，
请教一下各位高手如果想从app1.config中读取配置信息应该如何读取？
采用ConfigurationManager.AppSettings 属性似乎只能读取到app.config的配置信息。 

ExeConfigurationFileMap map = new ExeConfigurationFileMap();
            map.ExeConfigFilename = @"D:\App1.config";// 这里对应你app1文件的路径
            Configuration config = ConfigurationManager.OpenMappedExeConfiguration(map, ConfigurationUserLevel.None);
            string connstr = config.ConnectionStrings.ConnectionStrings["connStr"].ConnectionString;
            MessageBox.Show(connstr);
            string key = config.AppSettings.Settings["key"].Value;
            MessageBox.Show(key);

using System;
using System.Configuration;

namespace JADAY.Frame.Common
{
    public class ConfigHelper
    {
        /// <summary>
        ///  获取webconfig指定键的值
        /// </summary>
        /// <param name="key">指定键</param>
        /// <param name="defaultValue">当获取的值为空时返回该值</param>
        /// <returns></returns>
        public static string GetAppSettings(string key, string defaultValue = "")
        {
            var value = ConfigurationManager.AppSettings[key];//获取指定的配置信息
            return value == null ? defaultValue : value.ToStringValue();
        }
        /// <summary>
        ///  获取webconfig指定键的值
        /// </summary>
        /// <param name="name">指定名称</param>
        /// <param name="defaultValue">当获取的值为空时返回该值</param>
        /// <returns></returns>
        public static string GetConnectionString(string name, string defaultValue = "")
        {
            //获取指定的配置信息
            var value = ConfigurationManager.ConnectionStrings[name].ConnectionString;
            return value == null ? defaultValue : value.ToStringValue();
        }
        /// <summary>
        ///  获取App_Data中配置文件指定键的值
        /// </summary>
        /// <param name="key">键</param>
        /// <param name="defaultValue">默认值</param>
        /// <returns></returns>
        public static string GetAppDataAppSettings(string key, string defaultValue = "")
        {
            var map = new ExeConfigurationFileMap
                {
                    ExeConfigFilename = AppDomain.CurrentDomain.BaseDirectory + "\\App_Data\\App.config"
                };
            var config = ConfigurationManager.OpenMappedExeConfiguration(map, ConfigurationUserLevel.None);
            var value = config.AppSettings.Settings[key].Value;
            return value == null ? defaultValue : value.ToStringValue();
        }
        /// <summary>
        /// 获取App_Data中数据连接字符串
        /// </summary>
        /// <param name="name">数据连接名字</param>
        /// <param name="defaultValue">默认值</param>
        /// <returns></returns>
        public static string GetAppDataConnectionString(string name, string defaultValue = "")
        {
            var map = new ExeConfigurationFileMap
            {
                ExeConfigFilename = AppDomain.CurrentDomain.BaseDirectory + "\\App_Data\\App.config"
            };
            var config = ConfigurationManager.OpenMappedExeConfiguration(map, ConfigurationUserLevel.None);
            var value = config.ConnectionStrings.ConnectionStrings[name].ConnectionString;
            return value == null ? defaultValue : value.ToStringValue();
        }
    }
}