AppSettings not getting resolved via constructor injection

Question

I have the configuration in appsettings.json as follows:

{
"Logging": {
"IncludeScopes": false,
"LogLevel": {
  "Default": "Warning"
}
},
 "GatewaySettings": {
 "DBName": "StorageDb.sqlite",
 "DBSize": "100"    
 }
}

Here is the class to represent the configuration data

 public class GatewaySettings
 {
    public string DBName { get; set; }
    public string DBSize { get; set; }
 }

Configured service as follows:

  services.AddSingleton(Configuration.GetSection("GatewaySettings").Get<GatewaySettings>());

but I'm getting this error:

Value cannot be null. Parameter name: implementationInstance'

Code:

  public class SqlRepository
  {
        private readonly GatewaySettings _myConfiguration;

        public SqlRepository(GatewaySettings settings)
        {
              _myConfiguration = settings;
        }
  }

Dependency injection code:

var settings = new IOTGatewaySettings();
builder.Register(c => new SqlRepository(settings))

Background

I am hosting ASPNET CORE application as windows service, and .NET Framework is 4.6.1

Note: similar question appears here but there is no solution provided.System.ArgumentNullException: Value cannot be null, Parameter name: implementationInstance

Use IOptions<T> instead Reference Configuration in ASP.NET Core — Nkosi
– Nkosi, Commented Jun 18, 2018 at 14:05

gunr2171 · Accepted Answer · 2018-06-18 14:11:32Z

9

Don't add concrete data model classes into DI - use the IOptions<> framework.

In your startup:

services.AddOptions();

// parses the config section into your data model
services.Configure<GatewaySettings>(Configuration.GetSection("GatewaySettings"));

Now, in your class:

public class SqlRepository
{
    private readonly GatewaySettings _myConfiguration;
    public SqlRepository(IOptions<GatewaySettings> gatewayOptions)
    {
        _myConfiguration = gatewayOptions.Value;
        // optional null check here
    }
}

Note: if your project does not include the Microsoft.AspNetCore.All package, you will need to add another package Microsoft.Extensions.Options.ConfigurationExtensions to get this functionality.

answered Jun 18, 2018 at 14:11

gunr2171

17.7k26 gold badges68 silver badges102 bronze badges

Sign up to request clarification or add additional context in comments.

10 Comments

kudlatiger Over a year ago

I am getting this error Package Microsoft.AspNetCore.All 2.1.0 is not compatible with net461 (.NETFramework,Version=v4.6.1) / win7-x86. Package Microsoft.AspNetCore.All 2.1.0 supports: netcoreapp2.1 while adding Microsoft.AspNetCore.All

gunr2171 Over a year ago

What version of .Net Core are you using? Why are you using .Net 4.6.1?

kudlatiger Over a year ago

Yes, I am using 4.6.1

kudlatiger Over a year ago

Resolved. I suppose to add Microsoft.Extensions.Options.ConfigurationExtensions in .net standard project

kudlatiger Over a year ago

quick question: Now how do I register in SqlRepository in autofac? do I have to use aspnet core built in dependency injection?

|

Joe Audette · Accepted Answer · 2018-06-18 15:06:31Z

3

You should use IOptions of T

services.Configure<GatewaySettings>(Configuration.GetSection("GatewaySettings"));

  public class SqlRepository
  {
    private readonly GatewaySettings _myConfiguration;
    public SqlRepository(IOptions<GatewaySettings> settingsAccessor)
    {
          _myConfiguration = settingsAccessor.Value;
    }
  }

you need these packages

<PackageReference Include="Microsoft.Extensions.Options" Version="2.1.0" />
<PackageReference Include="Microsoft.Extensions.Options.ConfigurationExtensions" Version="2.1.0" />

Reference Options pattern in ASP.NET Core

edited Jun 18, 2018 at 15:06

answered Jun 18, 2018 at 14:09

Joe Audette

37.1k12 gold badges111 silver badges103 bronze badges

1 Comment

kudlatiger Over a year ago

What references we need to add to get IOptions? This is asp.net core application running as windows service

Collectives™ on Stack Overflow

AppSettings not getting resolved via constructor injection

2 Answers 2

10 Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

10 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related