您可以将 .Net 标准库添加到 PCL，但只能是较低版本.这取决于您的配置文件版本，因此您几乎必须尝试一下，看看它是否有效.

You can add .Net standard libraries to PCLs, but only lower versions. It depends on your profile version, so you almost have to try it and see if it works.

您可以将 PCL 添加到 .Net 标准库，方法是在您的 csproj 文件中设置 PCL 的回退.你可以在这里阅读:https://oren.codes/2017/04/23/using-xamarin-forms-with-net-standard-vs-2017-edition/

You can add PCLs to .Net standard libraries, by setting a fallback to the PCL in your csproj file. You can read about it here: https://oren.codes/2017/04/23/using-xamarin-forms-with-net-standard-vs-2017-edition/