What is the difference between Shared and Portable. When to choose these libraries.
All discussed here: https://developer.xamarin.com/guides/cross-platform/application_fundamentals/building_cross_platform_applications/sharing_code_options/
IMHO If your in doubt you want a PCL.
Shared libraries definitely have a place but its not as universal or as obvious. A shared Library isn't self sufficient it creates no artifacts when you compile it in fact you can't compile it without another project to compile it into. I think of Shared Projects like they are a collection of <#Include> files from ASP or PHP. A set of Interfaces or DataObjects POCOs for a database you need in multiple apps might be a good candidate for a shared Project. They are all basically Identical but in the context of the app they are actually logically different.
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