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[Bug]: Previewer Stopped #214
Description
Describe the bug
This is coming from a fresh install and a default MVVM project build
To Reproduce
Install Avalonia Community for Visual Studio Community, create a new MVVM project (.net9.0 for me, but I also tried 10 and 8), build it, and open MainWindow.axaml
Product(s)
Avalonia for Visual Studio
Platform
Windows
License Tier
Community
Avalonia version
12.3.2.0
Tool/Control Version
No response
Relevant log output
19:45:45.289 [Information] [AvaloniaPackage] Logging initialized.
19:45:45.295 [Information] [AvaloniaPackage] File logging enabled. Log file: C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Logs\VS_2026-10-12.log
19:45:45.302 [Information] [AuthenticationService] Restoring previous session: 10/16/2026 18:38:39 +00:00 / 10/26/2026 18:38:39 +00:00
19:45:45.307 [Debug] [AuthenticationService] Ticket was found from the subscription key.
19:45:45.315 [Information] [AuthenticationService] Restoring previous session: 10/16/2026 18:38:39 +00:00 / 10/26/2026 18:38:39 +00:00
19:45:45.316 [Debug] [AuthenticationService] Ticket was found from the subscription key.
19:45:45.316 [Information] [AuthenticationService] Restoring previous session: 10/16/2026 18:38:39 +00:00 / 10/26/2026 18:38:39 +00:00
19:45:45.317 [Debug] [AuthenticationService] Ticket was found from the subscription key.
19:45:45.317 [Information] [AuthenticationService] Restoring previous session: 10/16/2026 18:38:39 +00:00 / 10/26/2026 18:38:39 +00:00
19:45:45.318 [Debug] [AuthenticationService] Ticket was found from the subscription key.
19:45:45.320 [Debug] [AvaloniaToolboxService] Toolbox: advised selection events (cookie=19)
19:45:45.321 [Debug] [AvaloniaToolboxService] Captured existing toolbox frame at initialization
19:45:45.321 [Debug] [AvaloniaToolboxService] Toolbox visibility tracker initialized: frame captured=True, frame events cookie=4
19:45:45.322 [Debug] [AvaloniaPackage] Toolbox feature enabled; AvaloniaToolboxService constructed.
19:45:45.328 [Debug] [ParcelToolService] Checking for AvaloniaUI.Parcel tool availability
19:45:45.543 [Debug] [ParcelToolService] Parcel tool check completed. Available: False
19:45:45.546 [Debug] [OpenWithParcelCommand] Parcel tool availability: False
19:45:45.654 [Debug] [DebuggerEventsService] DebuggerEventsService initialized successfully
19:45:45.654 [Debug] [AvaloniaPackage] DebuggerEventsService initialized
19:45:45.655 [Debug] [AvaloniaPackage] OutputErrorsClearTriggerService initialized
19:45:45.658 [Debug] [AvaloniaPackage] Avalonia Package initialized
19:45:45.663 [Information] [AuthenticationService] Restoring previous session: 10/16/2026 18:38:39 +00:00 / 10/26/2026 18:38:39 +00:00
19:45:45.664 [Debug] [AuthenticationService] Ticket was found from the subscription key.
19:45:45.664 [Information] [AvaloniaPackage] Avalonia context activated. User signed in: True
19:45:46.235 [Warning] [AxamlClassifier (#3959276)] Could not get classifications: source not yet loaded.
19:45:46.289 [Debug] [AvaloniaToolboxViewCreationListener] AXAML view created; scheduling toolbox refresh.
19:45:46.292 [Debug] [AvaloniaToolboxService] Toolbox refresh requested (buffer True)
19:45:46.293 [Debug] [AvaloniaToolboxService] Toolbox refresh: license gate not satisfied; clearing any installed tabs
19:45:46.470 [Debug] [CpsProjectInfoService] Resolving target dependent projects via CPS for 'C:\Users\Nelson Garcia\source\AvaloniaApplication2\AvaloniaApplication2.csproj'
19:45:46.485 [Debug] [AvaloniaToolboxService] Toolbox refresh requested (buffer True)
19:45:46.485 [Debug] [AvaloniaToolboxService] Toolbox refresh: license gate not satisfied; clearing any installed tabs
19:45:46.486 [Debug] [AvaloniaToolboxService] Toolbox refresh requested (buffer True)
19:45:46.486 [Debug] [AvaloniaToolboxService] Toolbox refresh: license gate not satisfied; clearing any installed tabs
19:45:46.498 [Debug] [AvaloniaToolboxService] Toolbox visibility check: frame.IsVisible() → True
19:45:46.596 [Debug] [AvaloniaToolboxService] Toolbox refresh requested (buffer True)
19:45:46.596 [Debug] [AvaloniaToolboxService] Toolbox refresh: license gate not satisfied; clearing any installed tabs
19:45:46.601 [Debug] [AvaloniaToolboxService] Toolbox refresh requested (buffer True)
19:45:46.601 [Debug] [AvaloniaToolboxService] Toolbox refresh: license gate not satisfied; clearing any installed tabs
19:45:46.659 [Warning] [AxamlThicknessAdornmentTagger (#5052426)] Unable to obtain parsed XAML because the request returned null
19:45:46.659 [Warning] [AxamlColorAdornmentTagger (#42925716)] Unable to obtain parsed XAML because the request returned null
19:45:46.678 [Debug] [CpsProjectInfoService] Finished resolving dependent projects for 'C:\Users\Nelson Garcia\source\AvaloniaApplication2\AvaloniaApplication2.csproj'. Found 0 dependent projects.
19:45:46.859 [Information] [AuthenticationService] Restoring previous session: 10/16/2026 18:38:39 +00:00 / 10/26/2026 18:38:39 +00:00
19:45:46.860 [Debug] [AuthenticationService] Ticket was found from the subscription key.
19:45:46.860 [Information] [AvaloniaEditorWithPreview (#67029240)] User is signed in
19:45:46.912 [Information] [PreviewerProcessFactory] Resolving metadata for 'C:\Users\Nelson Garcia\source\AvaloniaApplication2\AvaloniaApplication2.csproj' (TFM=net9.0)
19:45:46.921 [Debug] [CpsAssetsPreviewerMetadataService] Resolving previewer metadata for 'C:\Users\Nelson Garcia\source\AvaloniaApplication2\AvaloniaApplication2.csproj' [net9.0]
19:45:45.658 [Debug] [AvaloniaPackage] Avalonia Package Loaded.
19:45:46.929 [Debug] [CpsAssetsPreviewerMetadataService] Resolving dependencies from 'C:\Users\Nelson Garcia\source\AvaloniaApplication2\bin\Debug\net9.0\AvaloniaApplication2.deps.json'.
19:45:46.937 [Information] [CpsAssetsPreviewerMetadataService] Resolving extra packages [Avalonia.Headless, Avalonia.Markup.Xaml.Loader] (Avalonia 12.1.2, net9.0)
19:45:47.348 [Information] [ShadowCopyOutputStrategy] Shadow copy reused at 'C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe' (4 files)
19:45:47.464 [Debug] [PreviewerProcess (#48527177)] > C:\Program Files\dotnet\dotnet.exe exec --runtimeconfig "C:\Users\Nelson Garcia\source\AvaloniaApplication2\bin\Debug\net9.0\AvaloniaApplication2.runtimeconfig.json" --depsfile "C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.previewer.deps.json" --additionalprobingpath "C:\Users\Nelson Garcia\.nuget\packages" --additionalprobingpath "C:\Program Files (x86)\Microsoft Visual Studio\Shared\NuGetPackages" "C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaUI.Previewer.HostApp.dll" --transport tcp-bson://127.0.0.1:51690/ "C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.dll"
19:45:47.464 [Information] [PreviewerProcess (#48527177)] Starting previewer process for target C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.dll (ShadowCopy=True, NewHostApp=True)
19:45:47.468 [Information] [PreviewerProcess (#48527177)] [8072] Started previewer process for 'C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.dll'. Waiting for connection to be initialized.
19:45:47.762 [Debug] [PreviewerProcess (#48527177)] [8072] Sending message: AvaloniaUI.Previewer.Protocol.UpdateXamlMessage
19:45:47.315 [Warning] [CpsAssetsPreviewerMetadataService] Failed to resolve force-include packages
AvaloniaUI.BuildTools.Utilities.DotNetRunnerException: MSBUILD : error MSB1001: Unknown switch.
at AvaloniaUI.BuildTools.Utilities.DotNetRunnerResult.ThrowIfError()
at AvaloniaUI.BuildTools.MSBuild.MSBuildProjectTools.<GetProjectMetadata>d__5.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at AvaloniaUI.Previewer.Process.Utilities.PreviewerForceIncludeResolver.<ResolveCoreAsync>d__5.MoveNext()
19:45:47.340 [Debug] [CpsAssetsPreviewerMetadataService] Resolve complete: 4 build outputs, 32 managed, 3 native, fingerprint=YSkwTXvdkAHNOCkp3daX+OfaF+FmyiZUC7POy3sm2UI=
19:45:47.735 [Error] [PreviewerProcess (#48527177)] [8072] <= Unhandled exception. System.IO.FileNotFoundException: Could not load file or assembly 'Avalonia.Headless, Version=12.0.0.0, Culture=neutral, PublicKeyToken=c8d484a7012f9a8b'. The system cannot find the file specified.
19:45:47.735 [Debug] [PreviewerProcess (#48527177)] [8072] <= Preparing transport
19:45:47.735 [Debug] [PreviewerProcess (#48527177)] [8072] <= Preparing Window Manager
19:45:47.735 [Debug] [PreviewerProcess (#48527177)] [8072] <= Initializing application in design mode
19:45:47.735 [Debug] [PreviewerProcess (#48527177)] [8072] <= Loading entry assembly
19:45:47.735 [Debug] [PreviewerProcess (#48527177)] [8072] <= Obtaining AppBuilder instance from AvaloniaApplication2
19:45:47.741 [Information] [PreviewerProcess (#48527177)] [8072] Connection initialized
19:45:47.747 [Debug] [PreviewerProcess (#48527177)] [8072] Sending message: AvaloniaUI.Previewer.Protocol.ClientSupportedPixelFormatsMessage
19:45:48.018 [Error] [PreviewerProcess (#48527177)] [8072] <= File name: 'Avalonia.Headless, Version=12.0.0.0, Culture=neutral, PublicKeyToken=c8d484a7012f9a8b'
19:45:48.018 [Error] [PreviewerProcess (#48527177)] [8072] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.<StartAvaloniaApplication>g__WithHeadless|4_1(AppBuilder appBuilder)
19:45:48.018 [Error] [PreviewerProcess (#48527177)] [8072] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.c(CommandLineArgs a)
19:45:48.019 [Error] [PreviewerProcess (#48527177)] [8072] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.a(String[] a)
19:45:48.020 [Error] [PreviewerProcess (#48527177)] [8072] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.Main(String[] cmdline)
19:45:48.020 [Error] [PreviewerProcess (#48527177)] [8072] <= at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
19:45:48.020 [Error] [PreviewerProcess (#48527177)] [8072] <= at System.Reflection.MethodInvoker.InvokeDirectByRefWithFewArgs(Object obj, Span`1 copyOfArgs)
19:45:48.020 [Error] [PreviewerProcess (#48527177)] [8072] <= at System.Reflection.MethodInvoker.InvokeDirectByRef(Object obj, Object arg1, Object arg2, Object arg3, Object arg4)
19:45:48.020 [Error] [PreviewerProcess (#48527177)] [8072] <= at System.Reflection.MethodInvoker.InvokeImpl(Object obj, Object arg1, Object arg2, Object arg3, Object arg4)
19:45:48.020 [Error] [PreviewerProcess (#48527177)] [8072] <= at System.Reflection.MethodInvoker.Invoke(Object obj, Span`1 arguments)
19:45:48.020 [Error] [PreviewerProcess (#48527177)] [8072] <= at Program.<Main>$(String[] args)
19:45:48.060 [Debug] [PreviewerProcess (#48527177)] [8072] Sending message: AvaloniaUI.Previewer.Protocol.UpdateXamlMessage
19:45:48.190 [Warning] [XamlClassificationSource (#61444888)] Parsed XAML was null during classification.
19:45:48.266 [Debug] [PreviewerProcess (#48527177)] [8072] Sending message: AvaloniaUI.Previewer.Protocol.UpdateXamlMessage
19:45:48.267 [Warning] [AxamlThicknessAdornmentTagger (#5052426)] Unable to obtain parsed XAML because the request returned null
19:45:48.267 [Warning] [AxamlColorAdornmentTagger (#42925716)] Unable to obtain parsed XAML because the request returned null
19:45:48.788 [Error] [PreviewerProcess (#48527177)] Connection error
System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
at System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult)
at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)
--- End of inner exception stack trace ---
at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)
at System.Threading.Tasks.TaskFactory`1.FromAsyncTrimPromise`1.Complete(TInstance thisRef, Func`3 endMethod, IAsyncResult asyncResult, Boolean requiresSynchronization)
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at AvaloniaUI.Previewer.Protocol.BsonStreamTransportConnection.<ReadExact>d__15.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at AvaloniaUI.Previewer.Protocol.BsonStreamTransportConnection.<Reader>d__16.MoveNext()
19:45:48.790 [Information] [PreviewerProcess (#48527177)] Process exited: GenericError
19:45:48.792 [Information] [PreviewerProcess (#48527177)] Stopping previewer process
19:45:50.474 [Error] [AvaloniaPreviewer (#48527177)] Error gating previewer XAML send on diagnostics
System.InvalidOperationException: Process not finished initializing.
at AvaloniaUI.Previewer.Process.PreviewerProcess.<UpdateXamlAsync>d__62.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at AvaloniaUI.VisualStudio.Extension.Views.AvaloniaPreviewer.<GateAndSendXamlAsync>d__103.MoveNext()
19:45:50.475 [Error] [AvaloniaPreviewer (#48527177)] Error gating previewer XAML send on diagnostics
System.InvalidOperationException: Process not finished initializing.
at AvaloniaUI.Previewer.Process.PreviewerProcess.<UpdateXamlAsync>d__62.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at AvaloniaUI.VisualStudio.Extension.Views.AvaloniaPreviewer.<GateAndSendXamlAsync>d__103.MoveNext()
19:46:06.587 [Debug] [EditorPane (#22776773)] Build started
19:46:08.289 [Debug] [EditorPane (#22776773)] Build finished
19:46:08.289 [Information] [PreviewerProcessFactory] Resolving metadata for 'C:\Users\Nelson Garcia\source\AvaloniaApplication2\AvaloniaApplication2.csproj' (TFM=net9.0)
19:46:08.289 [Debug] [CpsAssetsPreviewerMetadataService] Resolving previewer metadata for 'C:\Users\Nelson Garcia\source\AvaloniaApplication2\AvaloniaApplication2.csproj' [net9.0]
19:46:08.289 [Debug] [CpsAssetsPreviewerMetadataService] Resolving dependencies from 'C:\Users\Nelson Garcia\source\AvaloniaApplication2\bin\Debug\net9.0\AvaloniaApplication2.deps.json'.
19:46:08.293 [Information] [CpsAssetsPreviewerMetadataService] Resolving extra packages [Avalonia.Headless, Avalonia.Markup.Xaml.Loader] (Avalonia 12.1.2, net9.0)
19:46:08.297 [Debug] [CpsAssetsPreviewerMetadataService] Resolve complete: 4 build outputs, 32 managed, 3 native, fingerprint=BwBQevK+7k6bM8jk8P0XPcMvpfRHD8EXIcVBsJGLJ80=
19:46:08.335 [Information] [ShadowCopyOutputStrategy] Shadow copy created at 'C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe' (4 files)
19:46:08.349 [Debug] [PreviewerProcess (#48527177)] > C:\Program Files\dotnet\dotnet.exe exec --runtimeconfig "C:\Users\Nelson Garcia\source\AvaloniaApplication2\bin\Debug\net9.0\AvaloniaApplication2.runtimeconfig.json" --depsfile "C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.previewer.deps.json" --additionalprobingpath "C:\Users\Nelson Garcia\.nuget\packages" --additionalprobingpath "C:\Program Files (x86)\Microsoft Visual Studio\Shared\NuGetPackages" "C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaUI.Previewer.HostApp.dll" --transport tcp-bson://127.0.0.1:51708/ "C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.dll"
19:46:08.349 [Information] [PreviewerProcess (#48527177)] Starting previewer process for target C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.dll (ShadowCopy=True, NewHostApp=True)
19:46:08.356 [Information] [PreviewerProcess (#48527177)] [5708] Started previewer process for 'C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.dll'. Waiting for connection to be initialized.
19:46:08.461 [Debug] [PreviewerProcess (#48527177)] [5708] <= Preparing transport
19:46:08.489 [Information] [PreviewerProcess (#48527177)] [5708] Connection initialized
19:46:08.489 [Debug] [PreviewerProcess (#48527177)] [5708] Sending message: AvaloniaUI.Previewer.Protocol.ClientSupportedPixelFormatsMessage
19:46:08.489 [Debug] [PreviewerProcess (#48527177)] [5708] Sending message: AvaloniaUI.Previewer.Protocol.ClientRenderInfoMessage
19:46:08.489 [Debug] [PreviewerProcess (#48527177)] [5708] Sending message: AvaloniaUI.Previewer.Protocol.UpdateXamlMessage
19:46:08.489 [Debug] [PreviewerProcess (#48527177)] [5708] <= Preparing Window Manager
19:46:08.493 [Debug] [PreviewerProcess (#48527177)] [5708] <= Initializing application in design mode
19:46:08.497 [Debug] [PreviewerProcess (#48527177)] [5708] <= Loading entry assembly
19:46:08.501 [Debug] [PreviewerProcess (#48527177)] [5708] <= Obtaining AppBuilder instance from AvaloniaApplication2
19:46:08.537 [Error] [PreviewerProcess (#48527177)] [5708] <= Unhandled exception. System.IO.FileNotFoundException: Could not load file or assembly 'Avalonia.Headless, Version=12.0.0.0, Culture=neutral, PublicKeyToken=c8d484a7012f9a8b'. The system cannot find the file specified.
19:46:08.537 [Error] [PreviewerProcess (#48527177)] [5708] <= File name: 'Avalonia.Headless, Version=12.0.0.0, Culture=neutral, PublicKeyToken=c8d484a7012f9a8b'
19:46:08.537 [Error] [PreviewerProcess (#48527177)] [5708] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.<StartAvaloniaApplication>g__WithHeadless|4_1(AppBuilder appBuilder)
19:46:08.537 [Error] [PreviewerProcess (#48527177)] [5708] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.c(CommandLineArgs a)
19:46:08.537 [Error] [PreviewerProcess (#48527177)] [5708] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.a(String[] a)
19:46:08.537 [Error] [PreviewerProcess (#48527177)] [5708] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.Main(String[] cmdline)
19:46:08.537 [Error] [PreviewerProcess (#48527177)] [5708] <= at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
19:46:08.541 [Error] [PreviewerProcess (#48527177)] [5708] <= at System.Reflection.MethodInvoker.InvokeDirectByRefWithFewArgs(Object obj, Span`1 copyOfArgs)
19:46:08.541 [Error] [PreviewerProcess (#48527177)] [5708] <= at System.Reflection.MethodInvoker.InvokeDirectByRef(Object obj, Object arg1, Object arg2, Object arg3, Object arg4)
19:46:08.541 [Error] [PreviewerProcess (#48527177)] [5708] <= at System.Reflection.MethodInvoker.InvokeImpl(Object obj, Object arg1, Object arg2, Object arg3, Object arg4)
19:46:08.541 [Error] [PreviewerProcess (#48527177)] [5708] <= at System.Reflection.MethodInvoker.Invoke(Object obj, Span`1 arguments)
19:46:08.541 [Error] [PreviewerProcess (#48527177)] [5708] <= at Program.<Main>$(String[] args)
19:46:09.476 [Error] [PreviewerProcess (#48527177)] Connection error
System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
at System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult)
at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)
--- End of inner exception stack trace ---
at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)
at System.Threading.Tasks.TaskFactory`1.FromAsyncTrimPromise`1.Complete(TInstance thisRef, Func`3 endMethod, IAsyncResult asyncResult, Boolean requiresSynchronization)
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at AvaloniaUI.Previewer.Protocol.BsonStreamTransportConnection.<ReadExact>d__15.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at AvaloniaUI.Previewer.Protocol.BsonStreamTransportConnection.<Reader>d__16.MoveNext()
19:46:09.478 [Information] [PreviewerProcess (#48527177)] Process exited: GenericError
19:46:09.478 [Information] [PreviewerProcess (#48527177)] Stopping previewer process
19:46:51.540 [Information] [PreviewerProcessFactory] Resolving metadata for 'C:\Users\Nelson Garcia\source\AvaloniaApplication2\AvaloniaApplication2.csproj' (TFM=net9.0)
19:46:51.540 [Debug] [CpsAssetsPreviewerMetadataService] Resolving previewer metadata for 'C:\Users\Nelson Garcia\source\AvaloniaApplication2\AvaloniaApplication2.csproj' [net9.0]
19:46:51.551 [Information] [ShadowCopyOutputStrategy] Shadow copy reused at 'C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe' (4 files)
19:46:51.567 [Debug] [PreviewerProcess (#48527177)] > C:\Program Files\dotnet\dotnet.exe exec --runtimeconfig "C:\Users\Nelson Garcia\source\AvaloniaApplication2\bin\Debug\net9.0\AvaloniaApplication2.runtimeconfig.json" --depsfile "C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.previewer.deps.json" --additionalprobingpath "C:\Users\Nelson Garcia\.nuget\packages" --additionalprobingpath "C:\Program Files (x86)\Microsoft Visual Studio\Shared\NuGetPackages" "C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaUI.Previewer.HostApp.dll" --transport tcp-bson://127.0.0.1:51718/ "C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.dll"
19:46:51.567 [Information] [PreviewerProcess (#48527177)] Starting previewer process for target C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.dll (ShadowCopy=True, NewHostApp=True)
19:46:51.570 [Information] [PreviewerProcess (#48527177)] [8740] Started previewer process for 'C:\Users\Nelson Garcia\AppData\Local\AvaloniaUI\com.AvaloniaUI.Net.VisualStudio\Previewer\AvaloniaApplication2_4Pkr2af7O2uL7rCe\AvaloniaApplication2.dll'. Waiting for connection to be initialized.
19:46:51.540 [Debug] [CpsAssetsPreviewerMetadataService] Resolving dependencies from 'C:\Users\Nelson Garcia\source\AvaloniaApplication2\bin\Debug\net9.0\AvaloniaApplication2.deps.json'.
19:46:51.544 [Information] [CpsAssetsPreviewerMetadataService] Resolving extra packages [Avalonia.Headless, Avalonia.Markup.Xaml.Loader] (Avalonia 12.1.2, net9.0)
19:46:51.547 [Debug] [CpsAssetsPreviewerMetadataService] Resolve complete: 4 build outputs, 32 managed, 3 native, fingerprint=BwBQevK+7k6bM8jk8P0XPcMvpfRHD8EXIcVBsJGLJ80=
19:46:51.665 [Debug] [PreviewerProcess (#48527177)] [8740] <= Preparing transport
19:46:51.678 [Information] [PreviewerProcess (#48527177)] [8740] Connection initialized
19:46:51.678 [Debug] [PreviewerProcess (#48527177)] [8740] Sending message: AvaloniaUI.Previewer.Protocol.ClientSupportedPixelFormatsMessage
19:46:51.678 [Debug] [PreviewerProcess (#48527177)] [8740] Sending message: AvaloniaUI.Previewer.Protocol.ClientRenderInfoMessage
19:46:51.678 [Debug] [PreviewerProcess (#48527177)] [8740] Sending message: AvaloniaUI.Previewer.Protocol.UpdateXamlMessage
19:46:51.683 [Debug] [PreviewerProcess (#48527177)] [8740] <= Preparing Window Manager
19:46:51.685 [Debug] [PreviewerProcess (#48527177)] [8740] <= Initializing application in design mode
19:46:51.687 [Debug] [PreviewerProcess (#48527177)] [8740] <= Loading entry assembly
19:46:51.691 [Debug] [PreviewerProcess (#48527177)] [8740] <= Obtaining AppBuilder instance from AvaloniaApplication2
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= Unhandled exception. System.IO.FileNotFoundException: Could not load file or assembly 'Avalonia.Headless, Version=12.0.0.0, Culture=neutral, PublicKeyToken=c8d484a7012f9a8b'. The system cannot find the file specified.
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= File name: 'Avalonia.Headless, Version=12.0.0.0, Culture=neutral, PublicKeyToken=c8d484a7012f9a8b'
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.<StartAvaloniaApplication>g__WithHeadless|4_1(AppBuilder appBuilder)
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.c(CommandLineArgs a)
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.a(String[] a)
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= at AvaloniaUI.Previewer.DesignerSupport.EntryPoint.Main(String[] cmdline)
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= at System.Reflection.MethodInvoker.InvokeDirectByRefWithFewArgs(Object obj, Span`1 copyOfArgs)
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= at System.Reflection.MethodInvoker.InvokeDirectByRef(Object obj, Object arg1, Object arg2, Object arg3, Object arg4)
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= at System.Reflection.MethodInvoker.InvokeImpl(Object obj, Object arg1, Object arg2, Object arg3, Object arg4)
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= at System.Reflection.MethodInvoker.Invoke(Object obj, Span`1 arguments)
19:46:51.723 [Error] [PreviewerProcess (#48527177)] [8740] <= at Program.<Main>$(String[] args)
19:46:52.632 [Error] [PreviewerProcess (#48527177)] Connection error
System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
at System.Net.Sockets.Socket.EndReceive(IAsyncResult asyncResult)
at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)
--- End of inner exception stack trace ---
at System.Net.Sockets.NetworkStream.EndRead(IAsyncResult asyncResult)
at System.Threading.Tasks.TaskFactory`1.FromAsyncTrimPromise`1.Complete(TInstance thisRef, Func`3 endMethod, IAsyncResult asyncResult, Boolean requiresSynchronization)
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at AvaloniaUI.Previewer.Protocol.BsonStreamTransportConnection.<ReadExact>d__15.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at AvaloniaUI.Previewer.Protocol.BsonStreamTransportConnection.<Reader>d__16.MoveNext()
19:46:52.632 [Information] [PreviewerProcess (#48527177)] Process exited: GenericError
19:46:52.632 [Information] [PreviewerProcess (#48527177)] Stopping previewer processAdditional context
Visual Studio 2022 Community v17.14
Edition Windows 10 Home
Version 22H2
Installed on 6/26/2022
OS Build 19045.7291
Processor AMD Ryzen 9 5900XT 16-Core Processor 3.30 GHz
Installed RAM 32.0 GB
Storage 1.82 TB SSD Samsung SSD 970 EVO Plus 2TB, 238 GB SSD SanDisk SDSSDP256G, 233 GB SSD Samsung SSD 850 EVO 250GB, 3.73 TB SSD TEAM TM8FPW004T
Graphics Card NVIDIA GeForce RTX 3080 Ti (12 GB)
System Type 64-bit operating system, x64-based processor
Pen and touch No pen or touch input is available for this display
Activity
7 remaining items
bonimy commentedon Oct 14, 2026
Update: I migrated from VS2022 to VS2026 and the previewer here works. Will keep issue open as I'm sure VS2022 is still supposed to be in support.
mrlacey commentedon Oct 14, 2026
@bonimy thanks for the update and glad you found a solution.
Yes, 2022 is still supported. We'll investigate.
Out of interest, is there a reason you hadn't updated to VS2026 already?
bonimy commentedon Oct 14, 2026
I hadn't updated to VS2026 simply because 2022 was still working.
Anyway, after installing VS2026, Avalonia now works in VS2022. Not sure if that was exactly what caused the fix, but now I'm stumped.
For the record, before installing VS2026, when the issue was happening, I installed Avalonia through the Visual Studio 2022 Marketplace. When it didn't work, I tried through command line. Still failing, I uninstalled both, and tried marketplace again, where it continued to not work.
I don't know if it helps, but here are all of the extensions I have on VS2022:
If time permits, I will try uninstalling VS2026 and see if Avalonia fails again.
mrlacey commentedon Oct 15, 2026
@bonimy thanks for all the extra information.
I think the call stack in the original report will be the most useful. It looks like a problem in the communication between the previewer process (that creates the preview images) and the display of them in the IDE.
The good news is that you are no longer blocked by this, but we will still look to try and improve the reliability of the communication with the previewer process.
maxkatz6 commentedon Oct 15, 2026
@bonimy can you send "dotnet --info" output?
bonimy commentedon Oct 15, 2026
The info may not be accurate anymore, as I installed vs2026 and .net10
mrlacey commentedon Oct 30, 2026
Version 12.4 of the extension is now available and includes a fix for this issue.
Thanks for your patience while we released this fix.
We hope you don't encounter any more problems, but if you do, please let us know, and we'll address them as quickly as possible.