ConfigurationProvider with other dependencies

问题

I've implemented my customs IConfigurationProvider and IConfigurationSource.

public class MyConfigurationSource : IConfigurationSource
{
    public string Foo { get; set; }

    public IConfigurationProvider Build(IConfigurationBuilder builder)
    {
        return new MyConfigurationProvider(this);
    }
}

internal class MyConfigurationProvider : ConfigurationProvider
{
    public MyConfigurationSource Source { get; };

    public MyConfigurationProvider()
    {
        Source = source
    }

    public override void Load()
    {
        // I'd like to assign here my configuration data by using some dependencies
        Data = .... 
    }
}

I do the build of my Configuration in the Startup constructor (I override the configuration created by CreateDefaultBuilder):

var builder = new ConfigurationBuilder()
        .SetBasePath(env.ContentRootPath)
        .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
        .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
        .AddEnvironmentVariables()
        .AddMyConfiguration("myfoovalue")
        .Build();

Extension method:

public static IConfigurationBuilder AddMyConfiguration(this IConfigurationBuilder builder, string foo)
{
    return builder.Add(new MyConfigurationSource 
        {
            Foo = url
        });
}

I wish I could somehow inject services to be used in Load method. The problem here is that the configuration build is done in the Startup constructor. I can only inject dependencies that I have available in this constructor: IWebHostEnvironment, IHostEnvironment, IConfiguration and all I added when I built the WebHost. Also these dependencies would have to be passed the moment I call the AddMyConfiguration extension method. How could I use dependencies that don't even exist at that moment?

回答1:

A bit late answer.

It's obvious there's no way to use the container, that was built using Startup.ConfigureServices, in the MyConfigurationSource/MyConfigurationProvider simply because by the time ConfigurationBuilder.Build is invoked, ServiceCollection.BuildServiceProvider has not been invoked.

A typical workaround would be to create another instance of IServiceProvider with required configuration and use it inside MyConfiguration....

Something like

internal class MyConfigurationProvider : ConfigurationProvider
{
    public MyConfigurationSource Source { get; };

    public MyConfigurationProvider()
    {
        Source = source;
        ServiceProvider = BuildServiceProvider();
    }

    public override void Load()
    {
        // I'd like to assign here my configuration data by using some dependencies
        Data = ServiceProvider.GetRequiredService<IMyService>().GetData();
    }
    
    protected virtual void ConfigureServices(IServiceCollection services)
    {
        services.AddMyService();
        // etc.
    }

    private IServiceProvider BuildServiceProvider()
    {
        var services = new ServiceCollection();

        ConfigureServices(services);

        return services.BuildServiceProvider();
    }
}

but this might not always be appropriate so I would also consider setting the value directly (though I didn't find any official information about how good this approach is)

public class Startup
{
    public void Configure(IApplicationBuilder app)
    {
        ...
        app.SetupMyConfiguration();
        ...
    }
}

...

public static class ApplicationBuilderExtensions
{
    public static IApplicationBuilder SetupMyConfiguration(this IApplicationBuilder app)
    {
        var configuration = app
            .ApplicationServices
            .GetRequiredService<IConfiguration>(); // alternatively IOptions<MyOptions>

        var myService = app
            .ApplicationServices
            .GetRequiredService<IMyService>();

        configuration["MyKey"] = myService.GetData("MyKey");
    }
}

来源：https://stackoverflow.com/questions/62080399/configurationprovider-with-other-dependencies