Xamarin.Forms 未能找到路径“x:platforms”的一部分

https://stackoverflow.com/questions/45500269/xamarin-android-common-targets-error-could-not-find-a-part-of-the-path-plat

https://forums.xamarin.com/discussion/101908/getting-error-could-not-find-a-part-of-the-path-d-platforms-when-building-on-vsts