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

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。

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"
}
}

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));
}
}

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");

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;
}