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Everything is an error on VS2019 but not VS2017, why?

Phunction 231 Reputation points
2020-12-22T00:21:45.387+00:00

Hopefully someone can help, I have an android project, works fine with VS2017, but when I open it in VS2019 everything is red(ie: The type or namespace 'System' could not be found...).
All the references are shown with a yellow icon, unless I click on it then the icon goes away.
How do I track this down? Why does it work on 2017 but not 2019? I really need to get it to work on 2019 as 2017 is limited to Android 9.0 sdk.
I can't find any hint as to why it does not work, there is nothing in the Xamarin logs, if I try building I just get a build failed in the output window.

C#
C#
An object-oriented and type-safe programming language that has its roots in the C family of languages and includes support for component-oriented programming.
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Accepted answer
  1. Cole Xia (Shanghai Wicresoft Co,.Ltd.) 6,751 Reputation points
    2020-12-23T06:03:48.457+00:00

    Hello,

    Welcome to Microsoft Q&A!

    xamarin.googleplayservices.maps need dependencies of AndroidX , AndroidX is a replacement to the original Android Support Library , if you install both if them in your project , there will be conflict.

    You can remove Support library and migrate to AndroidX package .

    Check the details in this article : https://learn.microsoft.com/en-us/xamarin/android/platform/androidx

    Thank you.

    If the response is helpful, please click "Accept Answer" and upvote it.
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  1. Duane Arnold 3,216 Reputation points
    2020-12-22T07:18:03.09+00:00

    All the references are shown with a yellow icon, unless I click on it then the icon goes away.

    Then the project has none of the references to the DLL(s), like 'System' or any of the other DLL(s). I think you will need to use the Nuget's Restore feature to have the referenced DLL(s) restored to the project.

    https://learn.microsoft.com/en-us/nuget/consume-packages/package-restore

  2. Phunction 231 Reputation points
    2020-12-22T20:27:11.377+00:00

    I removed all my nuget packages and the 'system' errors went away (still had errors that referenced the nuget packages.)
    I then install the newer version of the nuget packages, namely Android.Support.V4 and google play services.
    Now, when I first install Android.Support.V4, it is OK, however, when I then try to install xamarin.googleplayservices.maps, everything breaks again. I have to remove all nuget packages.

    Is there a problem with running Android.Support.V4 and xamarin.googleplayservices.maps together?