引用依赖于ConfigurationManager的.net core 2中的.net框架程序集

Question

We have some legacy 4.5.2 class libraries that make common use of ConfigurationManager.AppSettings[key]

Is it possible to reference these within a .net core 2 application so that the config is correctly patched up under the hood? Ie the old calls into ConfigurationManager.AppSettings[key] correctly read the config, either from json or xml, but within the .netcore2 app.

If I port the keys of question to appSettings.json then the call into ConfigurationManager.AppSettings always returns null.

An example would be:

{
"Logging": {
    "IncludeScopes": false,
    "Debug": {
        "LogLevel": {
            "Default": "Warning"
        }
    },
    "Console": {
        "LogLevel": {
            "Default": "Warning"
        }
    }
},
"appSettings": {"test": "bo"},
"test": "hi"
}

And then:

[HttpGet]
public IEnumerable<string> Get()
{
    return new string[] { "value1", "value2", ConfigurationManager.AppSettings["test"] , ConfigurationManager.AppSettings["appSettings:test"] };
}

Will display:

["value1","value2",null,null]

Answer 1

The setup you are looking for is possible and the settings can be kept as-is in app.config.

I have a .NET 4.5.2 class library "MyLibrary" and a .NET Core 2.0 web application "WebApp" referencing the full .NET framework 4.6.1.

MyLibrary

• has an assembly reference to System.Configuration
• has a class Foo which reads an appsetting with key foo

WebApp

• has a project reference to MyLibrary
• has an assembly reference to System.Configuration
• has an app.config file containing the appSettings section. ( App.config is by default present in a .NET Core 2.0 web application project.)
• uses in instance of Foo , calls its GetSomething method by which the value bar gets assigned to the variable something .

All other files and settings are the default ones. Here below are the ones mentioned above.

---

MyLibrary project

.NET 4.5.2

Foo.cs

using System;
using System.Configuration;

namespace PFX
{
    public class Foo
    {
        public String GetSomething()
        {
            String r = ConfigurationManager.AppSettings["foo"];
            return r;
        }
    }
}

---

WebApp project

.NET Core 2.0.1 referencing full .NET framework 4.6.1.

WebApp.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">    
    <PropertyGroup>
        <TargetFramework>net461</TargetFramework>
    </PropertyGroup>

    <ItemGroup>
        <PackageReference Include="Microsoft.AspNetCore" Version="2.0.3" />
        <PackageReference Include="Microsoft.AspNetCore.Mvc" Version="2.0.4" />
        <PackageReference Include="Microsoft.AspNetCore.Mvc.Razor.ViewCompilation" Version="2.0.4" PrivateAssets="All" />
        <PackageReference Include="Microsoft.AspNetCore.StaticFiles" Version="2.0.3" />
        <PackageReference Include="Microsoft.VisualStudio.Web.BrowserLink" Version="2.0.3" />
    </ItemGroup>

    <ItemGroup>
        <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="2.0.4" />
     </ItemGroup>

     <ItemGroup>
        <ProjectReference Include="..\MyLibrary\MyLibrary.csproj" />
     </ItemGroup>

    <ItemGroup>
        <Reference Include="System.Configuration" />
    </ItemGroup>    
</Project>

App.config

<configuration>
    <runtime>
       <gcServer enabled="true"/>
    </runtime>

    <appSettings>
        <add key="foo" value="bar"/>
    </appSettings>
</configuration>

Program.cs

using System;
using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Hosting;

namespace WebApp
{
    public class Program
    {
        public static void Main(string[] args)
        {
            PFX.Foo foo = new PFX.Foo();
            String someting = foo.GetSomething(); // bar

            BuildWebHost(args).Run();
        }

        public static IWebHost BuildWebHost(String[] args) =>
            WebHost.CreateDefaultBuilder(args)
                .UseStartup<Startup>()
                .Build();
    }
}