error MSB4018: The "ResolveSdks" task failed unexpectedly.

[lt-gerjan]

Sorry for the little info but I want to file this issue right now. I hope to add more info later.

We have upgraded our build server (TeamCity) because we want to use .NET Core 3.0 RTM.
We upgraded it using the VS Installer.

But after this update, suddenly, TeamCity/MSBuild gives the following errors:

[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018: The "ResolveSdks" task failed unexpectedly. [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018: System.ArgumentNullException: Value cannot be null. [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018: Parameter name: path1 [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at System.IO.Path.Combine(String path1, String path2) [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at Xamarin.Android.Tools.AndroidSdkWindows.<GetAllAvailableAndroidNdks>d__44.MoveNext() [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at System.Linq.Enumerable.<DistinctIterator>d__64`1.MoveNext() [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at System.Linq.Buffer`1..ctor(IEnumerable`1 source) [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at System.Linq.Enumerable.ToArray[TSource](IEnumerable`1 source) [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at Xamarin.Android.Tools.AndroidSdkBase.get_AllAndroidNdks() [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at Xamarin.Android.Tools.AndroidSdkBase.Initialize(String androidSdkPath, String androidNdkPath, String javaSdkPath) [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at Xamarin.Android.Tools.AndroidSdkWindows.Initialize(String androidSdkPath, String androidNdkPath, String javaSdkPath) [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at Xamarin.Android.Tools.AndroidSdkInfo..ctor(Action`2 logger, String androidSdkPath, String androidNdkPath, String javaSdkPath) [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at Xamarin.Android.Tasks.MonoAndroidHelper.RefreshAndroidSdk(String sdkPath, String ndkPath, String javaPath, TaskLoggingHelper logHelper) [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at Xamarin.Android.Tasks.ResolveSdks.Execute() [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at Microsoft.Build.BackEnd.TaskExecutionHost.Microsoft.Build.BackEnd.ITaskExecutionHost.Execute() [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\MSBuild\Xamarin\Android\Xamarin.Android.Common.targets(798,2): error MSB4018:    at Microsoft.Build.BackEnd.TaskBuilder.<ExecuteInstantiatedTask>d__26.MoveNext() [D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj]
[23:20:46][CompileFramework] Done Building Project "D:\A2\work\c6a2c69e830880f1\src\LogicTrade\LogicTrade.StoreAssist.Pda.App\LogicTrade.StoreAssist.Pda.App.csproj" (Build;SignAndroidPackage target(s)) -- FAILED.
[23:20:46][CompileFramework] 
[23:20:46][CompileFramework] Build FAILED.

The builds before (this afternoon) were working just fine.

[pjcollins]

This looks like an error scenario which was improved by dotnet/android-tools#73.

I believe the core issue here is that the Android SDK path can no longer be resolved. When you ran the VS installer, did it install any Android SDK components?

If the Android SDK is not installed into a "well known" path on this CI machine (e.g. C:\Program Files (x86)\Android\android-sdk), then you can set the path to the Android SDK explicitly by using this msbuild property:

<AndroidSdkDirectory>C:\some\path</AndroidSdkDirectory>

or by passing /p:AndroidSdkDirectory="C:\some\path" to your command line build arguments.

I'm going to close this because I don't believe it's an issue with the Xamarin.Android SDK, but please feel free to reopen if you are unable to get things working after re-running the VS installer or explicitly setting the path to your custom SDK location.