问题
I started blank cross-platform projects in Visual Studio 2015 update 2: Visual C# -> Cross-platform -> Blank App (Xamarin.Forms portable).
It created 6 projects in the solution. Then I tried to update nugget packages for all of them. Needless to say the firs problem I encountered was the unnecessary reference to *design assemblies. I managed to corrected it.
Then I got following message when I see 6 nuget packages are ready to update, 5 of them are for Andriod, and 1 is the newer version of Xamarin.Forms.
Unable to resolve dependencies. 'Xamarin.Android.Support.Design 23.2.1' is not compatible with 'Xamarin.Forms 2.1.0.6529 constraint: Xamarin.Android.Support.Design (= 23.0.1.3)'.
So when Xamarin published new version of packages, there was no consideration of the compatibility among them?
回答1:
Xamarin Forms is not always compatible with the latest version of the Google Support libraries. Xamarin publishes them so Android developers (not using Forms) can utilize them if they need them, but Forms developers can continue to use the older, compatible versions.
回答2:
When I was trying to update the NuGet Packages for one of my Xamarin project, I got the error same as this..
Please check Compile framework and target framework of your android app.. and update your NuGet packages according to the properties of your android app. Below link describes how did I fix the issue.
https://xamarinsharp.com/2017/05/01/xamarin-android-support-design-25-3-1-is-not-compatible-with-xamarin-forms-2-3-4-231-constraint-xamarin-android-support-design-23-3-0-how-to-fix-it/
来源：https://stackoverflow.com/questions/36489766/cannot-upgrade-nuget-packages-for-xamarin-android