public class TopicConfig
{
        public string Project { get; set; } ="ibms";
        public string Device { get; set; } = "gateway";
        public string City { get; set; } = "wuhan";
        public string Area { get; set; } = "poly";
}

private TopicConfig topicConfig = new TopicConfig();

{
    "topic": {
        "Project": "ibms",
        "Device": "gateway",
        "City": "wuhan",
        "Area": "poly"
    }
}

private void LoadConfig()
        {
            var path = Directory.GetCurrentDirectory();
            var config_file = "appsettings.json";
            var full_path = Path.Combine(path, config_file);
            if (File.Exists(full_path))
            {
                var builder = new ConfigurationBuilder()
                    .SetBasePath(path)
                    .AddJsonFile("appsettings.json");

                IConfiguration Configuration = builder.Build();

                if (Configuration.GetSection(Topic).Exists())//Topic為字符串常量，對應(yīng)配置段屬性名稱
                    Configuration.GetSection(Topic).Bind(topicConfig);//綁定配置數(shù)據(jù)到配置類
            }
            else
            {
                SaveConfig();
            }
     }

private void SaveConfig(string path = "")
{
        if (path == "") path = Directory.GetCurrentDirectory();
        Dictionary<string, object> sectionsInfo = new Dictionary<string, object>();

        sectionsInfo.Add(Topic, topicConfig); //Topic為字符串常量，對應(yīng)配置段屬性名稱
        JsonConfigHelper.SaveJson(sectionsInfo, path);
}

using System;
using System.Collections.Generic;
using System.IO;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;

namespace flyfire.Common
{
    public class JsonConfigHelper
    {
        public static bool SaveJson(Dictionary<string,object> sectionInfo, string configFilePath, string configFileName = "appsettings.json")
        {
            if (sectionInfo.Count==0)
                return false;

            try
            {
                var filePath = Path.Combine(configFilePath, configFileName);
                JObject jsonObject;

                if (File.Exists(filePath))
                {
                    using (StreamReader file = new StreamReader(filePath))
                    {
                        using (JsonTextReader reader = new JsonTextReader(file))
                        {
                            jsonObject = (JObject)JToken.ReadFrom(reader);
                        }
                    }
                }
                else
                {
                    jsonObject = new JObject();
                }

                foreach (var key in sectionInfo.Keys)
                {
                    jsonObject[key] = JObject.FromObject(sectionInfo[key]);
                }

                using (var writer = new StreamWriter(filePath))
                using (JsonTextWriter jsonwriter = new JsonTextWriter(writer)
                {
                    Formatting = Formatting.Indented,//格式化縮進(jìn)
                    Indentation = 4,  //縮進(jìn)四個字符
                    IndentChar = ' '  //縮進(jìn)的字符是空格
                })
                {
                    jsonObject.WriteTo(jsonwriter);
                    return true;
                }
            }
            catch (Exception)
            {
                return false;
            }
        }
    }
}