在 ASP.NET Core3.1 中使用包含“System.Web.HttpContext”的旧项目

Question

We have some legacy projects, written with .Net Framework which should be used by an API project which is written by ASP.NET Core3.1. The problem is that these legacy projects are using 'System.Web.HttpContext' that you know does not exist in .net core anymore. Now we are receiving this error: ' Could not load type 'System.Web.HttpContext' from assembly 'System.Web , Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'.'
Have you faced this problem before? Can anyone help please?

Answer 1

.NET Framework libraries are not technically compatible with .NET Core. .NET Standard libraries are, and since both .NET Framework and .NET Core implement .NET Standard, Microsoft made a special exemption in the compiler to allow .NET Framework libraries to be referenced by projects that target .NET Core, with the caveat that they may not actually work. You get a warning to this effect when you reference a .NET Framework library from a .NET Core project.

The .NET Framework library will work as long as it only uses APIs compatible with .NET Standard 2.0. System.Web.HttpContext is not one such API, so it will not work in a .NET Core project. Period. Nothing you can do about that.

You can attempt to multi-target your libraries and sub-in .NET Core compatible APIs using compiler directives. That'll work, but gets messy quick. Otherwise, you'll just have to write new versions of the libraries for ASP.NET Core, since presumably you're trying to maintain support in the current libraries for ASP.NET.