需要IConfigurationRoot的ASP.NET Core 2.x注册服务-无法访问配置数据

Question

Configuration is registered in my app in Program.cs like so

public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
            WebHost.CreateDefaultBuilder(args)
                   .ConfigureAppConfiguration((hostingContext, config) =>
                   {
                       config.AddJsonFile("appsettings.secret.json", optional: true, reloadOnChange: true);
                   })
                   .UseStartup<Startup>()
                   .ConfigureLogging(logging =>
                   {override configuration in NLog.config

                       logging.ClearProviders();
                       logging.SetMinimumLevel(LogLevel.Trace);
                   })
                   .UseNLog(); // NLog: setup NLog for Dependency injection;

I have a class which requires an instance of IConfigurationRoot

public class ConfiguredKeyDataProtectionProvider : IDataProtectionProvider
{
    // Example configuration required for use of this class

    // {
    //     "ConfiguredKeyDataProtectionProvider": {
    //         "Key": {
    //             "TestPurpose": "asda2516shah"
    //         }
    //     }
    // }

    private readonly IConfigurationRoot _configurationRoot;

    public ConfiguredKeyDataProtectionProvider(IConfigurationRoot configurationRoot)
    {
        _configurationRoot = configurationRoot;
    }

    public IDataProtector CreateProtector(string purpose)
    {
        string encryptionKey = _configurationRoot.GetValue<string>("ConfiguredKeyDataProtectionProvider:Key:" + purpose);

        return new ConfiguredKeyDataProtector(encryptionKey);
    }
}

I'm trying to register the instance of IConfiguredKeyDataProtectionProvider via DI. I'm expecting that having registered an instance of IConfiguration root (note that reading of config files is duplicated in StartUp.cs - not sure if this is necessary), IConfiguredKeyDataProtectionProvider will be able to see the configuration data, but this appears not to be the case.

public class Startup
{
    public Startup(IHostingEnvironment env)
    {
        var configurationRoot = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json")
            .AddJsonFile("appsettings.secret.json", optional: true, reloadOnChange: true)
            .Build();

        Configuration = configurationRoot;
    }

    public IConfigurationRoot Configuration { get; set; }

    // This method gets called by the runtime. Use this method to add services to the container.
    // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddSingleton<IConfigurationRoot>(Configuration);

        //...

        services.AddTransient<IDataProtectionProvider, ConfiguredKeyDataProtectionProvider>();

How should I correctly configure my application so that classes with IConfigurationRoot on the constructor can be registered via dependency injection?

Answer 1

Not sure why you need the IConfigurationRoot interface, but since you have already built an instance of IConfigurationRoot before constructing the host, you could register the root as an singleton service by .ConfigureServices(services =>{services.AddSingleton<IConfigurationRoot>(configRoot);}) :

Also, there's no need to build the configuration twice, simply call UseConfiguration(congfigRoot) .

public static IWebHostBuilder CreateWebHostBuilder(string[] args) {

    // build the root 
    var configRoot = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("appsettings.json", optional: false)
        // ...
        .Build();

    var builder = new WebHostBuilder();
    return builder
        // reuse the configRoot
        .UseConfiguration(configRoot)
        // register the configRoot as a singleton service
        .ConfigureServices(services =>{
            services.AddSingleton<IConfigurationRoot>(configRoot);
        })
        .UseStartup<Startup>()
        .ConfigureLogging(logging => {   
            //override configuration in NLog.config
            logging.ClearProviders();
            logging.SetMinimumLevel(LogLevel.Trace);
        })
        .UseKestrel();
}