Table of Contents
.NET Version Overview
- .NET Standard 2.0 is a specification for a set of cross-platform APIs that all platform implementations of that standard must support.
- .NET Core 2.0 is a cross-platform implementation of that .NET Standard 2.0
- .NET Framework is a Windows-only implementation of various .NET APIs
- .NET Framework 4.7.1 fully implements .NET Standard 2.0
System.* Packages Dead-Ended from .NET Core 2.0
- In .NET Core 2.0, all the
System.*NuGet packages are effectively dead-ended - since they are now included as part of the 2.0 runtime. - Going forward your projects should not be referencing those
System.*packages
Referencing .NET Standard 2.0 Libraries
- Full .NET Framework 4.7.1 class libraries can reference any .NET Standard 2.0 (or earlier) library
- However, a .NET Standard 2.0 library cannot necessarily reference and use a full .NET Framework class library - because that library may no comply with the .NET Standard.
- It is estimated that at the time of the release of .NET Core 2.0, approximately 70% of existing NuGet packages can be used without an issue - BUT you won’t know there is an issue without thorough testing with that library!
- Microsoft has decided to emit a nice ugly compiler warning and warning signal against a reference in the Solution Explorer when this is the case.
- Recommendation: Use a full .NET Framework class library if you have references to any non .NET Standard class libraries - to avoid the compiler warning and ensure that the library does not have compatibility issues.
- .NET Framework 4.6.1 with the .NET Core 2.0 SDK installed also supports .NET Standard 2.0 - but due to the way that the libraries are packaged, this can cause assembly binding problems - so better to target 4.7.1 from the start.
- For example:
- When running under .NET Core 2, the Tuple type is in assembly:
System.ValueTuple, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e. - When running under .NET Framework 4.6.1, the Tuple type is in:
System.ValueTuple, System.ValueTuple, Version=4.0.2.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51. - But, when starting with a .NET Framework 4.6.1 application that uses a .NET Standard 2.0 library, the .NET Standard 2.0 code wants:
System.ValueTuple, Version=0.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51
- When running under .NET Core 2, the Tuple type is in assembly:
- If your application targeted 4.6.1 and .NET Framework 4.7.1 was later installed, any referenced .NET Standard libraries may experience
System.TypeLoadExceptionexceptions. The workaround being to re-target your application to 4.7.1.
- For example:
.NET Framework Libraries & Automatic Assembly Binding Redirects
- By default, assembly binding redirects aren’t added to full .NET Framework class library projects.
- This is problematic for unit testing projects as they are essentially like applications
- Add the following into the .csproj:
1<AutoGenerateBindingRedirects>true</AutoGenerateBindingRedirects> 2<GenerateBindingRedirectsOutputType>true</GenerateBindingRedirectsOutputType> - And then remove all the manual binding redirects from the app.config file
- See also: How to enable and disable automatic binding redirection
Compiler warnings
- With .NET Framework libraries referencing .NET Standard 2.0 libraries,
Microsoft.Extensions.DependencyInjection.Abstractionscauses a compiler warning:- “Resolved file has a bad image, no metadata, or is otherwise inaccessible. The system cannot find the path specified. (Exception from HRESULT: 0x80070003)”
- This should be fixed in a future .NET SDK update: Issue 1544 and Issue 1548