ASP.NET Core 选项模式源码学习Options Configure（一）

前言

ASP.NET Core 后我们的配置变得更加轻量级了，在ASP.NET Core中，配置模型得到了显著的扩展和增强，应用程序配置可以存储在多环境变量配置中，appsettings.json用户机密等 并可以通过应用程序中的相同界面轻松访问，除此之外，ASP.NET中的新配置系统允许使用Options的强类型设置。

强类型Options

在ASP.NET Core中没有AppSettings["Key"]默认方法，那么推荐的是创建强类型的配置类，去绑定配置项。

    public class MyOptions
    {
        public string Name { get; set; }

        public string Url { get; set; }
    }

然后我们在appsettings.json中添加如下内容：

{
  "MyOptions": 
    {
      "Name": "TestName",
      "Url": "TestUrl"
    }
}

配置绑定到类

ConfigureServices方法进行配置以绑定到类

        public void ConfigureServices(IServiceCollection services)
        {

            services.Configure<MyOptions>(Configuration.GetSection("MyOptions"));
            services.AddControllers();

        }

MyOptions只需将IOptions<>类的实例注入控制器中，然后通过Value属性获取Myoptions：

    public class WeatherForecastController : ControllerBase
    {
        private readonly MyOptions _options;
        public WeatherForecastController(IOptions<MyOptions> options)
        {
            _options = options.Value;
        }

        [HttpGet]
        public OkObjectResult Get() {
            return Ok(string.Format("Name:{0},Url:{1}", _options.Name,_options.Url));
        }
    }

Configure

委托配置

            //基础注册方式
            services.Configure<MyOptions>(o => { o.Url = "MyOptions"; o.Name = "Name111"; });
            //指定具体名称
            services.Configure<MyOptions>("Option", o => { o.Url = "MyOptions"; o.Name = "Name111"; }) ;
            //配置所有实例
            services.ConfigureAll<MyOptions>(options =>{ options.Name = "Name1";  options.Url = "Url1";});

通过配置文件配置

           // 使用配置文件来注册实例
            services.Configure<MyOptions>(Configuration.GetSection("MyOptions"));
            // 指定具体名称
            services.Configure<MyOptions>("Option", Configuration.GetSection("MyOptions"));

PostConfigure

PostConfigure会在Configure注册完之后再进行注册

     services.PostConfigure<MyOptions>(o => o.Name = "Name1");
            services.PostConfigure<MyOptions>("Option", o => o.Name = "Name1");
            services.PostConfigureAll<MyOptions>(o => o.Name = "Name1");

源码解析

IConfigureOptions接口

    public interface IConfigureOptions<in TOptions> where TOptions : class
    {
        
        void Configure(TOptions options);
    }

Configure为方便使用IConfigureOptions注册单例ConfigureNamedOptions

     public static IServiceCollection Configure<TOptions>(this IServiceCollection services, string name, Action<TOptions> configureOptions)
            where TOptions : class
        {
            if (services == null)
            {
                throw new ArgumentNullException(nameof(services));
            }

            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            services.AddOptions();
            services.AddSingleton<IConfigureOptions<TOptions>>(new ConfigureNamedOptions<TOptions>(name, configureOptions));
            return services;
        }

上面代码IConfigureOptions实现了ConfigureNamedOptions，那我们再来看看内部源码
ConfigureNamedOptions 其实就是把我们注册的Action包装成统一的Configure方法，以方便后续创建Options实例时，进行初始化。

    public class ConfigureNamedOptions<TOptions> : IConfigureNamedOptions<TOptions> where TOptions : class
    {
        
        public ConfigureNamedOptions(string name, Action<TOptions> action)
        {
            Name = name;
            Action = action;
        }

       
        public string Name { get; }

      
        public Action<TOptions> Action { get; }

      
        public virtual void Configure(string name, TOptions options)
        {
            if (options == null)
            {
                throw new ArgumentNullException(nameof(options));
            }

            // Null name is used to configure all named options.
            if (Name == null || name == Name)
            {
                Action?.Invoke(options);
            }
        }
        public void Configure(TOptions options) => Configure(Options.DefaultName, options);
    }

在 services.Configure(Configuration.GetSection("MyOptions")); 我们不指定具体名称的时候默认是如下代码片段

        public virtual void Configure(string name, TOptions options)
        {
            if (options == null)
            {
                throw new ArgumentNullException(nameof(options));
            }

            // Null name is used to configure all named options.
            if (Name == null || name == Name)
            {
                Action?.Invoke(options);
            }
        }
        public void Configure(TOptions options) => Configure(Options.DefaultName, options);

默认使用的是Options.DefaultName

AddOptions默认方法默认为我们注册了一些核心的类

     public static IServiceCollection AddOptions(this IServiceCollection services)
        {
            if (services == null)
            {
                throw new ArgumentNullException(nameof(services));
            }

            services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptions<>), typeof(OptionsManager<>)));
            services.TryAdd(ServiceDescriptor.Scoped(typeof(IOptionsSnapshot<>), typeof(OptionsManager<>)));
            services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptionsMonitor<>), typeof(OptionsMonitor<>)));
            services.TryAdd(ServiceDescriptor.Transient(typeof(IOptionsFactory<>), typeof(OptionsFactory<>)));
            services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptionsMonitorCache<>), typeof(OptionsCache<>)));
            return services;
        }
        

来源：https://www.cnblogs.com/yyfh/archive/2019/12/11/12020522.html