reference .Net framework 4.5.2 from .Net Core 2.0 project

Question

I have spent a few hours trying to figure out why .Net Core 2.0 wouldn't load .Net framework 4.5.2 nuget packages.

Now I think it's time to ask...

What happens is I have a .Net Core 2.0 WebApi app (A) and I want to reuse my .Net framework 4.5.2 library(B).

I created nuget packages for B and referenced the nuget package in the A.

The libraries are downloaded in the C:\Users\username.nuget\packages folder But when I consume B in the code, it errors me out saying

System.IO.FileLoadException: 'Could not load file or assembly 'xxx.TradeServices.Common, Version=2.1.289.1, Culture=neutral, PublicKeyToken=null'. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)'

I then added some dummy code

var client = new TradeServicesClient(EnvironmentType.Production);

xxx.TradeServices.Common is loaded.

But another exception appear saying cannot load dependency dll.

FileNotFoundException: Could not load file or assembly 'Ice, Version=3.7.0.0, Culture=neutral, PublicKeyToken=0c5ebb72d74932c6'. The system cannot find the file specified.

I have checked all the dependencies, they are downloaded correctly in the

C:\Users\username.nuget\packages

folder

I am not sure about why .Net Core is behaving this way. It seems the dependency chain is not loaded. Could you please help me to figure out what's going on?

Answer 1

asp.net core can target multiple frameworks; a 2.0 web app will typically run on either "netcoreapp2.0" (a .NET Core application) or "net461" (a .NET application), for example - as specified by the <TargetFramework> in the csproj. It is this <TargetFramework> that determines how all the downstream package resolution will work. If it is "net461", it may be happy to take a "net452" library. However, "netcoreapp2.0" will not want "net452" - instead preferring "netstandard2.0" or "netstandard1.6", etc. Targeting .NET Standard will mean that all downstream packages also need to target .NET Standard, which is not always possible.

So:

• if possible, make your dependencies target some version of .NET Standard
• if that isn't possible, ensure that the <TargetFramework> is "net461" or similar

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Edit: it looks like the default projects also change between Microsoft.AspNetCore (when targeting .NET) and Microsoft.AspNetCore.All (when targeting .NET Core) - so you may also need to change that <PackageReference ... /> entry in the csproj. If you are using any of the extra packages in Microsoft.AspNetCore.All that aren't in Microsoft.AspNetCore - you may need to add the ones that you need manually.