为什么.NET Core选项的配置不适用于泛型类型参数？

Question

I have a .NET Core WebApi project. To read the appsettings in an easy way, I configure the options to be injected with DI. This works fine. However if I try to call Configure<>() with a generic type parameter, I get an error.

Argument 2: cannot convert from 'Microsoft.Extensions.Configuration.IConfigurationSection' to 'System.Action'

The method overloads apart from Configure<T>(Action<T> configureOptions) seem not to be available anymore.

Why does the call not work with generic type parameters?

Startup.cs

public class Startup
{
    public IConfiguration Configuration { get; }

    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public void ConfigureServices(IServiceCollection services)
    {
        // services.AddMvc() etc...

        services.AddOptions();

        // Works fine
        services.Configure<MyOption>(Configuration.GetSection(nameof(MyOption)));
    }

    private void AddOption<T>(IServiceCollection services)
    {
        // Wont work
        services.Configure<T>(Configuration.GetSection(nameof(T)));
        services.Configure<T>(Configuration.GetSection(""));
    }
}

MyOption.cs

public class MyOption
{
    public bool MyProp { get; set; }
}

appsettings.json

{
    "MyOption": {
        "MyProp": true
    }
}

Answer 1

You need to change your function AddOption like that:

private void AddOption<T>(IServiceCollection services) where T : class 
{
    services.Configure<T>(Configuration.GetSection(typeof(T).Name));
}

you forgot about where T : class in the method declaration

And after you can use this method like there:

AddOption<MyOption>(services);

Answer 2

Apparently, nameof(T) would simply return the string "T".

You need to use typeof(T).Name instead:

services.Configure<T>(Configuration.GetSection(typeof(T).Name));

See Documentation

Answer 3

If you want to become a good programmer, then learn to read errors and rummage through the documentations and implementations of libraries, and not write for every reason here. @igor-cova has already given you the right answer. The next time, be careful because writing this question took much more time and effort than you yourself would have looked into the implementation of the Configure method. Good luck Regards, Andrew

Answer 4

You need to use services.Configure as below:

services.Configure<MyOption>(setting =>
{  
    Configuration.GetSection("MyOption").Bind(setting);  
});