Xamarin.Forms does not compile an Android Project

Question

Again, after updating to VS 8.9.1 on Mac I'm getting this error while trying to compile my Android project:

    /Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Tooling.targets(5,5): Error XARSD7023: System.IO.DirectoryNotFoundException: Could not find a part of the path '/Users/giulioserra/Library/Android/sdk'.
  at System.IO.Enumeration.FileSystemEnumerator`1[TResult].CreateDirectoryHandle (System.String path, System.Boolean ignoreNotFound) [0x00032] in <36514b14425c4337b446653c547aa9c3>:0 
  at System.IO.Enumeration.FileSystemEnumerator`1[TResult]..ctor (System.String directory, System.IO.EnumerationOptions options) [0x00048] in <36514b14425c4337b446653c547aa9c3>:0 
  at System.IO.Enumeration.FileSystemEnumerable`1+DelegateEnumerator[TResult]..ctor (System.IO.Enumeration.FileSystemEnumerable`1[TResult] enumerable) [0x00000] in <36514b14425c4337b446653c547aa9c3>:0 
  at System.IO.Enumeration.FileSystemEnumerable`1[TResult]..ctor (System.String directory, System.IO.Enumeration.FileSystemEnumerable`1+FindTransform[TResult] transform, System.IO.EnumerationOptions options) [0x00042] in <36514b14425c4337b446653c547aa9c3>:0 
  at System.IO.Enumeration.FileSystemEnumerableFactory.UserDirectories (System.String directory, System.String expression, System.IO.EnumerationOptions options) [0x00014] in /Users/builder/jenkins/workspace/build-package-osx-mono/2020-02/external/bockbuild/builds/mono-x64/external/corefx/src/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemEnumerableFactory.cs:104 
  at System.IO.Directory.InternalEnumeratePaths (System.String path, System.String searchPattern, System.IO.SearchTarget searchTarget, System.IO.EnumerationOptions options) [0x00045] in /Users/builder/jenkins/workspace/build-package-osx-mono/2020-02/external/bockbuild/builds/mono-x64/external/corefx/src/System.IO.FileSystem/src/System/IO/Directory.cs:180 
  at System.IO.Directory.EnumerateDirectories (System.String path, System.String searchPattern, System.IO.EnumerationOptions enumerationOptions) [0x00000] in /Users/builder/jenkins/workspace/build-package-osx-mono/2020-02/external/bockbuild/builds/mono-x64/external/corefx/src/System.IO.FileSystem/src/System/IO/Directory.cs:196 
  at System.IO.Directory.EnumerateDirectories (System.String path, System.String searchPattern, System.IO.SearchOption searchOption) [0x00000] in /Users/builder/jenkins/workspace/build-package-osx-mono/2020-02/external/bockbuild/builds/mono-x64/external/corefx/src/System.IO.FileSystem/src/System/IO/Directory.cs:193 
  at Xamarin.Android.Tools.AndroidSdkBase.FindBestNDK (System.String androidSdkPath) [0x00038] in /Users/builder/azdo/_work/278/s/xamarin-android/external/xamarin-android-tools/src/Xamarin.Android.Tools.AndroidSdk/Sdks/AndroidSdkBase.cs:172 
  at Xamarin.Android.Tools.AndroidSdkBase+<GetAllAvailableAndroidNdks>d__73.MoveNext () [0x000d0] in /Users/builder/azdo/_work/278/s/xamarin-android/external/xamarin-android-tools/src/Xamarin.Android.Tools.AndroidSdk/Sdks/AndroidSdkBase.cs:164 
  at Xamarin.Android.Tools.AndroidSdkBase.GetValidNdkPath (System.String ctorParam) [0x00068] in /Users/builder/azdo/_work/278/s/xamarin-android/external/xamarin-android-tools/src/Xamarin.Android.Tools.AndroidSdk/Sdks/AndroidSdkBase.cs:128 
  at Xamarin.Android.Tools.AndroidSdkBase.Initialize (System.String androidSdkPath, System.String androidNdkPath, System.String javaSdkPath) [0x00061] in /Users/builder/azdo/_work/278/s/xamarin-android/external/xamarin-android-tools/src/Xamarin.Android.Tools.AndroidSdk/Sdks/AndroidSdkBase.cs:71 
  at Xamarin.Android.Tools.AndroidSdkInfo..ctor (System.Action`2[T1,T2] logger, System.String androidSdkPath, System.String androidNdkPath, System.String javaSdkPath) [0x00025] in /Users/builder/azdo/_work/278/s/xamarin-android/external/xamarin-android-tools/src/Xamarin.Android.Tools.AndroidSdk/AndroidSdkInfo.cs:18 
  at Xamarin.Android.Tasks.MonoAndroidHelper.RefreshAndroidSdk (System.String sdkPath, System.String ndkPath, System.String javaPath, Microsoft.Build.Utilities.TaskLoggingHelper logHelper) [0x00005] in <e0b267300cf54583bbaa8d3ab5dc4081>:0 
  at Xamarin.Android.Tasks.ResolveSdks.RunTask () [0x000ac] in <e0b267300cf54583bbaa8d3ab5dc4081>:0 
  at Xamarin.Android.Tasks.AndroidTask.Execute () [0x00000] in <e0b267300cf54583bbaa8d3ab5dc4081>:0  (XARSD7023) (HangoverBusiness.Android)

I tried to delete bin and obj files but nothing, this problem only manifests in the Android project, while the IOS version works fine.

Env: Mac OS Catalina VS 8.9.1

Any hint?

Answer 1

Workaround is now added in prerelease.

https://learn.microsoft.com/en-us/visualstudio/releasenotes/vs2019-mac-preview-relnotes

Workaround:- In some cases, Android projects may fail to build with an error The Java SDK could not be found, please set the path to it in the Xamarin.Android SDKs settings panel. A workaround is to execute the following command in a Terminal:

mkdir -p ~/Library/Android/sdk

Answer 2

Looking at the developer community portal this is a bug introduced in v8.9.1. It also specifies a workaround: manually copy the Android SDK files from the default path (found in the settings screen, see below) to the hardcoded path in the error message. In your case /Users/giulioserra/Library/Android/sdk