给 IConfiguration 写一个 GetAppSetting 扩展方法

Intro

在 .net core 中，微软已经默认使用 appsettings.json 来代替 app.config，并重新设计了一套完整的配置系统，可以支持 json/xml/ini/环境变量等。

在 .net core 中有一个 GetConnectionString 的扩展方法用来比较方便的获取链接字符串，类似于在 .net framework 中使用 ConfigurationManager.ConnectionStrings["key"] 来获取链接字符串。

这次来参考 GetConnectionString 实现一个 GetAppSetting，类似于 .net framework 中使用 ConfigurationManager.AppSettings 来获取配置值。

实现代码

GetConnectionString 是获取 ConnectionStrings 这个节点下的某个配置，
GetAppSetting 来获取 AppSettings 这个节点下的某个配置

实现代码：

        /// <summary>
        /// GetAppSetting
        /// Shorthand for GetSection("AppSettings")[key]
        /// </summary>
        /// <param name="configuration">IConfiguration instance</param>
        /// <param name="key">appSettings key</param>
        /// <returns>app setting value</returns>
        public static string GetAppSetting([NotNull]this IConfiguration configuration, string key)
        {
            return configuration.GetSection("AppSettings")[key];
        }

        /// <summary>
        /// GetAppSetting
        /// Shorthand for GetSection("AppSettings")[key]
        /// </summary>
        /// <param name="configuration">IConfiguration instance</param>
        /// <param name="key">appSettings key</param>
        /// <returns>app setting value</returns>
        public static T GetAppSetting<T>([NotNull]this IConfiguration configuration, string key)
        {
            return configuration.GetSection("AppSettings")[key].To<T>();
        }

        /// <summary>
        /// GetAppSetting
        /// Shorthand for GetSection("AppSettings")[key]
        /// </summary>
        /// <param name="configuration">IConfiguration instance</param>
        /// <param name="key">appSettings key</param>
        /// <param name="defaultValue">default value if not exist</param>
        /// <returns>app setting value</returns>
        public static T GetAppSetting<T>([NotNull] this IConfiguration configuration, string key, T defaultValue)
        {
            return configuration.GetSection("AppSettings")[key].ToOrDefault(defaultValue);
        }

        /// <summary>
        /// GetAppSetting
        /// Shorthand for GetSection("AppSettings")[key]
        /// </summary>
        /// <param name="configuration">IConfiguration instance</param>
        /// <param name="key">appSettings key</param>
        /// <param name="defaultValueFunc">default value func if not exist to get a default value</param>
        /// <returns>app setting value</returns>
        public static T GetAppSetting<T>([NotNull] this IConfiguration configuration, string key, Func<T> defaultValueFunc)
        {
            return configuration.GetSection("AppSettings")[key].ToOrDefault(defaultValueFunc);
        }

查看源码

使用

使用起来和 GetConnectionString 差不多

测试 appsettings.json

{
  "ConnectionStrings": {
    "TestDb": "server=.;database=Test;uid=weihanli;pwd=Admin888"
  },
  "AppSettings":{
    "Number": 12,
    "City": "Shanghai"
  }
}

GetAppSetting 示例

        IConfiguration configuration = new ConfigurationBuilder()
            // ...
            .AddJsonFile("appsettings.json")
            .Build();

        var city = configuration.GetAppSetting("City");
        var number = configuration.GetAppSetting<int>("Number");
        System.Console.WriteLine($"City:{city}, Number:{number}");