我有一个Xamarin.Forms解决方案，但经过一些清洁和建设，我无法再编译我的Xamarin.iOS项目了。 该项目最近从PCL迁移到VS2017中的.NET Standard 1.6项目，并在早期版本中成功编译。我能够在调试模式下在iOS模拟器中编译和运行，但经过一些清理和构建（以及添加和删除一些NuGet包）后，我也无法在此模式下运行。
Environment variables being passed to the tool:
2> Xamarin.iOS 11.6.1 using framework: /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator10.2.sdk
2>C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(777,3): error : Could not link assemblies. Reason: Object reference not set to an instance of an object
2> Tool /Library/Frameworks/Xamarin.iOS.framework/Versions/Current/bin/mtouch execution finished.
2> MTouch: 2017-12-28T11:56:33.4882016-07:00 - Finalizado
2>Ejecución de la tarea "MTouch" terminada -- ERROR.
2>Compilación terminada del destino "_CompileToNative" en el proyecto "MyApp.iOS.csproj" -- ERROR.
2>
2>ERROR al compilar.
2>
2>"C:\_Sources\MyApp\MyApp\MyApp.iOS\MyApp.iOS.csproj" (destino predeterminado) (1) ->
2>(_CoreCompileImageAssets destino) ->
2> C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(1198,3): warning : The app icon set "AppIcons" has an unassigned child.
2>
2>
2>"C:\_Sources\MyApp\MyApp\MyApp.iOS\MyApp.iOS.csproj" (destino predeterminado) (1) ->
2>(_CompileToNative destino) ->
2> C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\MSBuild\Xamarin\iOS\Xamarin.iOS.Common.targets(777,3): error : Could not link assemblies. Reason: Object reference not set to an instance of an object
有什么想法吗？ 我正在使用VS Community 2017，版本15.5.2 VisualStudio.15.Release / 15.5.2 + 27130.2010