一.概述
本章讲的选项模式是对Configuration配置的功能扩展。 讲这篇时有个专用名词叫“选项类(TOptions)” 。该选项类作用是指：把选项类中的属性与配置来源中的键关联起来。举个例，假设json文件有个Option1键，选项类中也有个叫Option1的属性名，经过选项配置，这样就能把json中的键的值映射到选项类属性值中。也可以理解在项目应用中，把一个json文件序列化到.net类。
1.1选项接口介绍
在官方文档中选项接口有很多，这里列举了这些选项接口。所有选项接口基本都继承了TOptions接口。
???// Used for notifications when TOptions instances change ???public interface IOptionsMonitor<out TOptions> ???{ ???????// ???????// 摘要: ???????// ????Returns the current TOptions instance with the Microsoft.Extensions.Options.Options.DefaultName. ???????TOptions CurrentValue { get; } ???????//... ???} ???// Used to create TOptions instances ???public interface IOptionsFactory<TOptions> where TOptions : class, new() ???{ ???????// ???????// 摘要: ???????// ????Returns a configured TOptions instance with the given name. ???????TOptions Create(string name); ???} ???// Represents something that configures the TOptions type. Note: These are run before all ????public interface IConfigureOptions<in TOptions> where TOptions : class ???{ ???????// ???????// 摘要: ???????// ????Invoked to configure a TOptions instance. ???????// ???????// 参数: ???????// ??options: ???????// ????The options instance to configure. ???????void Configure(TOptions options); ???} ???public interface IPostConfigureOptions<in TOptions> where TOptions : class ???{ ???????// ???????// 摘要: ???????// ????Invoked to configure a TOptions instance. ???????// ???????// 参数: ???????// ??name: ???????// ????The name of the options instance being configured. ???????// ???????// ??options: ???????// ????The options instance to configured. ???????void PostConfigure(string name, TOptions options); ???} ???public interface IConfigureNamedOptions<in TOptions> : IConfigureOptions<TOptions> where TOptions : class ???{ ???????// ???????// 摘要: ???????// ????Invoked to configure a TOptions instance. ???????// ???????// 参数: ???????// ??name: ???????// ????The name of the options instance being configured. ???????// ???????// ??options: ???????// ????The options instance to configure. ???????void Configure(string name, TOptions options); ???} ???// Used by IOptionsMonitor<TOptions> to cache TOptions instances. ???public interface IOptionsMonitorCache<TOptions> where TOptions : class ???{ ???????// ???????// 摘要: ???????// ????Clears all options instances from the cache. ???????void Clear(); ???????// ???????// 摘要: ???????// ????Gets a named options instance, or adds a new instance created with createOptions. ???????// ???????// 参数: ???????// ??name: ???????// ????The name of the options instance. ???????// ???????// ??createOptions: ???????// ????The func used to create the new instance. ???????// ???????// 返回结果: ???????// ????The options instance. ???????TOptions GetOrAdd(string name, Func<TOptions> createOptions); ???????// ???????// 摘要: ???????// ????Tries to adds a new option to the cache, will return false if the name already ???????// ????exists. ???????// ???????// 参数: ???????// ??name: ???????// ????The name of the options instance. ???????// ???????// ??options: ???????// ????The options instance. ???????// ???????// 返回结果: ???????// ????Whether anything was added. ???????bool TryAdd(string name, TOptions options); ???????// ???????// 摘要: ???????// ????Try to remove an options instance. ???????// ???????// 参数: ???????// ??name: ???????// ????The name of the options instance. ???????// ???????// 返回结果: ???????// ????Whether anything was removed. ???????bool TryRemove(string name); ???} ???// Used to access the value of TOptions for the lifetime of a request ???public interface IOptionsSnapshot<out TOptions> : IOptions<TOptions> where TOptions : class, new() ???{ ???????// ???????// 摘要: ???????// ????Returns a configured TOptions instance with the given name. ???????TOptions Get(string name); ???} ???//Used to retrieve configured TOptions instances ???public interface IOptions<out TOptions> where TOptions : class, new() ???{ ???????// ???????// 摘要: ???????// ????The default configured TOptions instance ???????TOptions Value { get; } ???}(1) IOptionsMonitor<TOptions>
IOptionsMonitor<TOptions>用于TOptions实例更改时的通知，用于管理 TOptions选项类 。该IOptionsMonitor<TOptions>支持以下方案：
(1) 更改通知。当配置文件发生修改时，会监听同步到选项类。
(2) 命名选项。IConfigureNamedOptions支持命名选项。接口继续关系 IConfigureNamedOptions:IConfigureOptions
(3) 重新加载配置。通过 IOptionsSnapshot 重新加载配置数据，IOptionsMonitor也支持该功能。 接口继续关系IOptionsSnapshot ：IOptions
(4) 选择性选项失效 (IOptionsMonitorCache<TOptions>)。
(2) 其它接口
IOptionsFactory<TOptions> 负责产生TOptions选项实例，它具有单个 Create 方法。
默认实现采用所有已注册 IConfigureOptions<TOptions> 和 IPostConfigureOptions<TOptions> 并首先运行所有配置(所有的来源配置)，
然后才进行选项后期配置IPostConfigureOptions<TOptions> 。
IOptionsMonitorCache<TOptions>用于缓存TOptions实例。
1.2 常规选项配置
TOptions选项类必须为包含公共无参数构造函数的非抽象类。下面示例中选项类MyOptions具有两种属性：Option1 和 Option2。 设置默认值为可选，但以下示例中的类构造函数设置了 Option1 的默认值。 Option2 具有通过直接初始化属性设置的默认值。
public class MyOptions ?? { ????? ?public MyOptions() ?????? { ??????????? // Set default value. ?????????? Option1 = "value1_from_ctor"; ?????? } ?????? public string Option1 { get; set; } ?????? public int Option2 { get; set; } = 5; ??? }??????//将MyOptions类已通过Configure添加到服务容器，并绑定到配置IConfiguration上 ??????//Registers a configuration instance which TOptions will bind against. ??????services.Configure<MyOptions>(Configuration);
???????private readonly MyOptions _options;
//OtherPages/Page1 ???????public Page1Model( IOptionsMonitor<MyOptions> optionsAccessor) ???????{ ???????????_options = optionsAccessor.CurrentValue; ???????} ?????????????public void OnGet() { ???????????var option1 = _options.Option1; ???????????var option2 = _options.Option2; ???????????var ?SimpleOptions = $"option1 = {option1}, option2 = {option2}"; ???????｝
// 此时SimpleOptions值："option1 = value1_from_ctor, option2 = 5"
??? //下面在appsettings.json 文件添加 option1 和 option2 的值。 ????? "option1": "value1_from_json", ????? "option2": -1,
当配置文件appsettings.json中option1和option2键的值改变后，MyOptions 选项类中的属性option1和option2的值也会改变。 下面再次运行OtherPages/Page1
//此时SimpleOptions的值为："option1 = value1_from_json, option2 = -1"
为什么MyOptions类中option1,option2会取到appsettings.json文件中的值呢？因为MyOptions选项类注入到Iconfiguration服务后与appsettings.json文件中键相同,形成了映射。
1.3 通过委托配置简单选项
使用委托设置选项值。 此示例应用使用 MyOptionsWithDelegateConfig 类 ,这里仍然是使用相同的键Option1，Option2。 它通过 MyOptionsWithDelegateConfig 使用委托来配置绑定。
?? public class MyOptionsWithDelegateConfig { ?? public MyOptionsWithDelegateConfig() ?? { ????? // Set default value. ?????? Option1 = "value1_from_ctor"; ? ? } ????????? public string Option1 { get; set; } ?????? public int Option2 { get; set; } = 5; } ????????services.Configure<MyOptions>(Configuration); ????????//第二个注入服务 ????????services.Configure<MyOptionsWithDelegateConfig>(myOptions => ????????{
// 在Page1Model构造方法中生成MyOptionsWithDelegateConfig实例时调用 ???????????????myOptions.Option1 = "value1_configured_by_delegate"; ???????????????myOptions.Option2 = 500; ????????});
public Page1Model( ???????????IConfiguration configuration, ???????????IOptionsMonitor<MyOptionsWithDelegateConfig> optionsAccessorWithDelegateConfig, ???????????IOptionsMonitor<MyOptions> optionsAccessor ?????????) ???????{ ???????????????????_optionsWithDelegateConfig = optionsAccessorWithDelegateConfig.CurrentValue; ???????????_options = optionsAccessor.CurrentValue; ???????????Configuration = configuration; ???????} ???????public IConfiguration Configuration { get; } ???????private readonly MyOptions _options; ???????private readonly MyOptionsWithDelegateConfig _optionsWithDelegateConfig; ???????public string BindGUIDMsg { get; set; } ???????public void OnGet() ???????{ ???????????BindGUIDMsg = $"option1 = {_options.Option1}, option2 = {_options.Option2}"; ???????????BindGUIDMsg += "</br>"; ???????????BindGUIDMsg += $"delegate_option1 = {_optionsWithDelegateConfig.Option1}, " + ??????????????????????????$"delegate_option2 = {_optionsWithDelegateConfig.Option2}"; ???????}每次调用 Configure 都会将 IConfigureOptions<TOptions> 服务添加到服务容器。 在前面的示例中，Option1 和 Option2 的值同时在 appsettings.json 中指定，但 Option1 和 Option2 的值被配置的委托替代。
当启用多个配置服务时，指定的最后一个配置源优于其他源，由其设置配置值。 运行应用时，页面模型的 OnGet 方法返回显示选项类值的字符串:
// myOptions实例取值如下: SimpleOptions：option1 = -1，option2 = 5 // MyOptionsWithDelegateConfig实例取值如下: delegate_option1 = value1_configured_by_delegate，delegate_option2 = 500
1.4 子选项配置
当配置文件中的子节点需要与选项类进行关联映射时，可以通过服务注入bind到指定的Configuration节点。在以下代码中，已向服务容器添加第三个 IConfigureOptions<TOptions> 服务。 它将 MySubOptions 绑定到 appsettings.json 文件的 subsection 部分：
? "Option1": "value1_from_json", ? "Option2": -1, ? "subsection": { ??? "suboption1": "subvalue1_from_json", ???? "suboption2": 200 ? } ?? public class MySubOptions ?? { ?????? public MySubOptions() ??????? { ????????? ?// Set default values. ?????????? SubOption1 = "value1_from_ctor"; ?????????? SubOption2 = 5; ?????? } ?????? public string SubOption1 { get; set; } ??????? public int SubOption2 { get; set; } ? ?}//第三个IConfigureOptions<TOptions>注入服务 ????????services.Configure<MySubOptions>(Configuration.GetSection("subsection")); ???//OtherPages/Page1 ??????????????????public Page1Model( ???????????IConfiguration configuration, ???????????IOptionsMonitor<MyOptionsWithDelegateConfig> optionsAccessorWithDelegateConfig, ???????????IOptionsMonitor<MyOptions> optionsAccessor, ???????????IOptionsMonitor<MySubOptions> subOptionsAccessor ?????????) ???????{ ???????????????????_optionsWithDelegateConfig = optionsAccessorWithDelegateConfig.CurrentValue; ???????????_options = optionsAccessor.CurrentValue; ???????????_subOptions = subOptionsAccessor.CurrentValue; ???????????Configuration = configuration; ???????} ???????public IConfiguration Configuration { get; } ???????private readonly MyOptions _options; ???????private readonly MyOptionsWithDelegateConfig _optionsWithDelegateConfig; ???????private readonly MySubOptions _subOptions; ??????// OnGet方法 ??? SubOptions = $"subOption1 = {_subOptions.SubOption1}, subOption2 = {_subOptions.SubOption2}"??? //运行应用时，OnGet 方法返回显示子选项类值的字符串： ??? // MySubOptions实例取值如下: ?? subOption1 = subvalue1_from_json，subOption2 = 200
1.5 IConfigureNamedOptions选项命名
IConfigureNamedOptions：是用于对选项类在注入服务时，进行命名。下面是把MyOptions选项类注入到服务，并取了别名named_options_1。 如下所示：
??? services.Configure<MyOptions>("named_options_1", Configuration); //在要使用的页面，如下所示： private readonly MyOptions _named_options_1; public IndexModel( ??? IOptionsSnapshot<MyOptions> namedOptionsAccessor) { ?? _named_options_1 = namedOptionsAccessor.Get("named_options_1"); } ?? // IOptionsSnapshot源码 ?? public interface IOptionsSnapshot<out TOptions> : IOptions<TOptions> where TOptions : class, new() ?? { ????? ?// ?????? // 摘要: ????? ?// ????Returns a configured TOptions instance with the given name. ?????? TOptions Get(string name); ?? }1.6 ConfigureAll
上面介绍的选项类，在注入服务时都是使用的services.Configure，它是针对选项类的当前实例，例如：在page1和page2都使用了实例MyOptions( private readonly MyOptions _options)但它们属于不同的实例。
??? //使用 ConfigureAll 方法配置所有选项实例 ???????????services.ConfigureAll<MyOptions>(myOptions => ???????????{ ???????????????//所有MyOptions实例配置 Option1的值 ???????????????myOptions.Option1 = "ConfigureAll replacement value"; ???????????});??? //添加代码后运行示例应用将产生以下结果： ??? named_options_1: option1 = ConfigureAll replacement value, option2 = -1 ??? named_options_2: option1 = ConfigureAll replacement value, option2 = 5
总结:
选项模式是对Configuration配置的功能扩展，主要用于把json文件序列化到.net类(选项类)。通过注入services. Configure或services.ConfigureAll把选项类注入到服务并绑定到Configuration上。 选项这篇还有其它功能如：选项后期配置( IPostConfigureOptions), 启动期间访问选项, 选项验证等，详细了解查看官网
参考文献
官方资料:asp.net core 选项
asp.net core 系列 12 选项 TOptions
原文地址：https://www.cnblogs.com/MrHSR/p/10291766.html