C#•5d ago

✅ Can custom attributes use interfaces somehow ?

I have an interface named IConfiguration and I'm wondering is it possible to write a custom attribute so I can do [StaticConfiguration("Key"]var settings: Settings so that the StaticConfiguration attribute will get the config for that key from IConfiguration and parse it into the type Settings?

10 Replies

mg•5d ago

you can't place attributes on local variables

JackoOP•5d ago

Sorry it doesn't need to be a local variable, it can be Settings settings;

mg•5d ago

it's possible to use reflection to set the value of that member variable yeah; it's also possible to get the attributes on that member variable, so you'll have to figure out how to put it all together i'm not sure where interfaces come into play

JackoOP•5d ago

I’m using dependency injection and I need the StaticConfiguration class to get the values from an interface of type IConfiguration

mg•5d ago

what's your end goal? do you have something like

public class MyService
{
  public Settings Settings { get; set; }
}

public class MyService
{
  public Settings Settings { get; set; }
}

and you want Settings to be set based on something you get from dependency injection?

JackoOP•5d ago

Yeah exactly

jcotton42•5d ago

$options

MODiX•5d ago

appsettings.json:

{
  "My": {
    "Foo": {
      "Kix": 5
    }
  }
}

{
  "My": {
    "Foo": {
      "Kix": 5
    }
  }
}

src/Foo/FooOptions.cs:

public class FooOptions
{
  public const string SectionName = "My:Foo";

  public string Bar {get;set;} = "default value for bar";
  public int Kix {get;set;} = -1;
  public DateTime? Pouet {get;set;} = default;
}

public class FooOptions
{
  public const string SectionName = "My:Foo";

  public string Bar {get;set;} = "default value for bar";
  public int Kix {get;set;} = -1;
  public DateTime? Pouet {get;set;} = default;
}

src/Foo/FooServiceCollectionExtensions.cs:

namespace Microsoft.Extensions.DependencyInjection; // <==== recommanded for service.Add so that you don't clutter Startup file

public class FooServiceCollectionExtensions
{
  public static IServiceCollection AddFoo(this IServiceCollection services) =>
    services
      .AddOptions<FooOptions>()
      .BindConfiguration(FooOptions.SectionName)
      .Validate(options => options.Kix >= 0, $"The configuration key '{FooOptions.SectionName}:{nameof(Kix)}' cannot be negative")
      ;

  public static IServiceCollection AddFoo(this IServiceCollection services, Action<FooOptions> configure) =>
    services
      .AddFoo()
      .Configure(configure);

namespace Microsoft.Extensions.DependencyInjection; // <==== recommanded for service.Add so that you don't clutter Startup file

public class FooServiceCollectionExtensions
{
  public static IServiceCollection AddFoo(this IServiceCollection services) =>
    services
      .AddOptions<FooOptions>()
      .BindConfiguration(FooOptions.SectionName)
      .Validate(options => options.Kix >= 0, $"The configuration key '{FooOptions.SectionName}:{nameof(Kix)}' cannot be negative")
      ;

  public static IServiceCollection AddFoo(this IServiceCollection services, Action<FooOptions> configure) =>
    services
      .AddFoo()
      .Configure(configure);

Program.cs / Startup.cs:

services.AddFoo();
// or
services.AddFoo(fooOptions => fooOptions.Kix = 12);

services.AddFoo();
// or
services.AddFoo(fooOptions => fooOptions.Kix = 12);

Bar.cs:

public class Bar
{
  private readonly FooOptions _fooOptions;

  // .Value in ctor is fine only if it's always ever a non-changing value (no reload and/or no scoped resolution)
  public Bar(IOptions<FooOptions> fooOptions)
    => _fooOptions = fooOptions.Value;
}

public class Bar
{
  private readonly FooOptions _fooOptions;

  // .Value in ctor is fine only if it's always ever a non-changing value (no reload and/or no scoped resolution)
  public Bar(IOptions<FooOptions> fooOptions)
    => _fooOptions = fooOptions.Value;
}

mg•5d ago

Unknown User•5d ago

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✅ Can custom attributes use interfaces somehow ?

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