问题
I'm trying to use System.Linq because it has an 'Unknown resolve error'. I've done a bit of looking around on how to do this and all I can find is people saying that it needs to be added or that they added it. I'm wondering how to add it to my project so that I can use the '.ToList' function.
回答1:
If you are doing a traditional iOS or Android project with Xamarin Studio, by default a reference to System.Core should already be added.
However, if you're creating a PCL you will see a reference to it, but it will be red in the References folder. This is because PCLs are not fully supported yet. There is a work around though.
You can copy the Core DLL from your Mono install and reference it in your PCL project. I was able to find this PCL on my Mac here: /Library/Frameworks/Mono.framework/Versions/3.0.10/lib/mono/4.0 - mscorlib.dll
I usually have a folder called "DLLs" inside my project folder that I put these type of DLLs and reference.
Hopefully in the near future we won't have to mess with hacks like this with PCLs.
来源：https://stackoverflow.com/questions/16747774/how-do-i-add-a-system-core-dll-reference-to-my-project-in-xamarin-studio-monodev