问题
After updating my VS 2017 to the latest version, when I create a new Xamarin app it loads with errors. The surprising bit is that when I open an app created before I updated the IDE, it loads perfectly. Can anyone help? Below are the errors:
Error CS0012 The type 'AppCompatActivity' is defined in an assembly that is not referenced. You must add a reference to assembly 'Xamarin.Android.Support.v7.AppCompat, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
Error CS0012 The type 'AppCompatActivity' is defined in an assembly that is not referenced. You must add a reference to assembly 'Xamarin.Android.Support.v7.AppCompat, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
Error CS0012 The type 'AppCompatActivity' is defined in an assembly that is not referenced. You must add a reference to assembly 'Xamarin.Android.Support.v7.AppCompat, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
Error CS0012 The type 'AppCompatActivity' is defined in an assembly that is not referenced. You must add a reference to assembly 'Xamarin.Android.Support.v7.AppCompat, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
Error CS0012 The type 'AppCompatActivity' is defined in an assembly that is not referenced. You must add a reference to assembly 'Xamarin.Android.Support.v7.AppCompat, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
Error CS0012 The type 'AppCompatActivity' is defined in an assembly that is not referenced. You must add a reference to assembly 'Xamarin.Android.Support.v7.AppCompat, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
Error CS0012 The type 'AppCompatActivity' is defined in an assembly that is not referenced. You must add a reference to assembly 'Xamarin.Android.Support.v7.AppCompat, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
Error CS0012 The type 'AppCompatActivity' is defined in an assembly that is not referenced. You must add a reference to assembly 'Xamarin.Android.Support.v7.AppCompat, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
Error CS0012 The type 'AppCompatActivity' is defined in an assembly that is not referenced. You must add a reference to assembly 'Xamarin.Android.Support.v7.AppCompat, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
Error CS0012 The type 'AppCompatActivity' is defined in an assembly that is not referenced. You must add a reference to assembly 'Xamarin.Android.Support.v7.AppCompat, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
Error CS0012 The type 'AppCompatActivity' is defined in an assembly that is not referenced. You must add a reference to assembly 'Xamarin.Android.Support.v7.AppCompat, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
Error CS0103 The name 'InitializeComponent' does not exist in the current context App2ButtonImages.iOS D:\Kajambiya\2017\Xamarin\App2ButtonImages\App2ButtonImages\App2ButtonImages\App.xaml.cs 14 Active.
Error NU1202 Package Xamarin.Android.Support.v7.MediaRouter 25.4.0.2 is not compatible with monoandroid60 (MonoAndroid,Version=v6.0). Package Xamarin.Android.Support.v7.MediaRouter 25.4.0.2 supports: monoandroid70 (MonoAndroid,Version=v7.0)
Error NU1202 Package Xamarin.Android.Support.v7.CardView 25.4.0.2 is not compatible with monoandroid60 (MonoAndroid,Version=v6.0). Package Xamarin.Android.Support.v7.CardView 25.4.0.2 supports: monoandroid70 (MonoAndroid,Version=v7.0)
Error NU1202 Package Xamarin.Android.Support.v7.AppCompat 25.4.0.2 is not compatible with monoandroid60 (MonoAndroid,Version=v6.0). Package Xamarin.Android.Support.v7.AppCompat 25.4.0.2 supports: monoandroid70 (MonoAndroid,Version=v7.0)
Error NU1202 Package Xamarin.Android.Support.v4 25.4.0.2 is not compatible with monoandroid60 (MonoAndroid,Version=v6.0). Package Xamarin.Android.Support.v4 25.4.0.2 supports: monoandroid70 (MonoAndroid,Version=v7.0)
Error NU1202 Package Xamarin.Android.Support.Design 25.4.0.2 is not compatible with monoandroid60 (MonoAndroid,Version=v6.0). Package Xamarin.Android.Support.Design 25.4.0.2 supports: monoandroid70 (MonoAndroid,Version=v7.0)
回答1:
I think at least the first errors speaks for it self, you need to add the nuget package
Xamarin.Android.Support.v7.AppCompat
The other errors point towards needing to build against a newer Android SDK, which you probably don't have installed.
回答2:
I have uninstall all AppCompatActivity packages from NuGet and it works with me
来源：https://stackoverflow.com/questions/47988647/xamarin-error-after-updating-visual-studio-2017-to-version-15-5-2