Trigger live reload feature after successful builds in VS

src/Microsoft.AspNetCore.Blazor.Build/targets/Blazor.MonoRuntime.targets

@@ -59,10 +59,16 @@
   -->
   <Target Name="_BlazorIssueLiveReloadNotification"
           AfterTargets="Build"
-          Condition="'$(UseBlazorLiveReloading)'=='true' AND '$(_BlazorDidCopyFilesToOutputDirectory)'=='true' AND '$(BuildingInsideVisualStudio)'!='true'">
-    <!-- Touch the signal file to trigger a reload -->
-    <WriteLinesToFile File="$(ProjectDir)$(OutputPath)$(BlazorBuildCompletedSignalPath)" Lines="_" />
-    <Delete Files="$(ProjectDir)$(OutputPath)$(BlazorBuildCompletedSignalPath)" />
+          Condition="'$(UseBlazorLiveReloading)'=='true' AND '$(_BlazorDidCopyFilesToOutputDirectory)'=='true'">
+    <PropertyGroup>
+      <_BlazorBuildCompletedSignalFullPath>$(ProjectDir)$(OutputPath)$(BlazorBuildCompletedSignalPath)</_BlazorBuildCompletedSignalFullPath>
+    </PropertyGroup>
+    <!--
+      If this is a command-line build, touch the signal file to trigger a reload.
+      If it's a VS build, then the VS extension will write the signal file instead.
+    -->
+    <WriteLinesToFile Condition="'$(BuildingInsideVisualStudio)'!='true'" File="$(_BlazorBuildCompletedSignalFullPath)" Lines="_" />
+    <Delete Condition="'$(BuildingInsideVisualStudio)'!='true'" Files="$(_BlazorBuildCompletedSignalFullPath)" />
   </Target>
 
   <!-- Preparing blazor files for output:

tooling/Microsoft.VisualStudio.BlazorExtension/BlazorPackage.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Runtime.InteropServices;
 using Microsoft.VisualStudio.Shell;
+using Microsoft.VisualStudio.Shell.Interop;
 
 namespace Microsoft.VisualStudio.BlazorExtension
 {
@@ -11,8 +12,24 @@ namespace Microsoft.VisualStudio.BlazorExtension
     [PackageRegistration(UseManagedResourcesOnly = true)]
     [AboutDialogInfo(PackageGuidString, "ASP.NET Core Blazor Language Services", "#110", "112")]
     [Guid(BlazorPackage.PackageGuidString)]
+    [ProvideAutoLoad(UIContextGuids80.SolutionExists)]
     public sealed class BlazorPackage : Package
     {
         public const string PackageGuidString = "d9fe04bc-57a7-4107-915e-3a5c2f9e19fb";
+
+        protected override void Initialize()
+        {
+            base.Initialize();
+            RegisterLiveReloadBuildWatcher();
+        }
+
+        private void RegisterLiveReloadBuildWatcher()
+        {
+            // No need to unadvise, as this only happens once anyway
+            ThreadHelper.ThrowIfNotOnUIThread();
+            var buildManager = (IVsSolutionBuildManager)GetService(typeof(SVsSolutionBuildManager));
+            var hr = buildManager.AdviseUpdateSolutionEvents(new LiveReloadBuildWatcher(), out var cookie);
+            Marshal.ThrowExceptionForHR(hr);
+        }
     }
 }

tooling/Microsoft.VisualStudio.BlazorExtension/LiveReloadBuildWatcher.cs

@@ -0,0 +1,109 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Microsoft.VisualStudio.ProjectSystem.Properties;
+using Microsoft.VisualStudio.Shell;
+using Microsoft.VisualStudio.Shell.Interop;
+using System;
+using System.Collections.Generic;
+using System.IO;
+
+namespace Microsoft.VisualStudio.BlazorExtension
+{
+    internal class LiveReloadBuildWatcher : IVsUpdateSolutionEvents2
+    {
+        const string BlazorProjectCapability = "Blazor";
+
+        private bool _isListeningForProjectBuilds = false;
+        private List<string> _signalFilePathsToNotify = new List<string>();
+
+        public int UpdateSolution_Begin(ref int pfCancelUpdate)
+        {
+            _signalFilePathsToNotify.Clear();
+            _isListeningForProjectBuilds = true;
+            return VSConstants.S_OK;
+        }
+
+        public int UpdateSolution_Done(int fSucceeded, int fModified, int fCancelCommand)
+        {
+            _isListeningForProjectBuilds = false;
+
+            foreach (var fullPath in _signalFilePathsToNotify)
+            {
+                try
+                {
+                    File.WriteAllText(fullPath, string.Empty);
+                    File.Delete(fullPath);
+                }
+                catch (Exception ex)
+                {
+                    AttemptLogError($"Blazor live reloading was unable to write to the signal " +
+                        $"file at {fullPath}. To disable live reloading, set the property " +
+                        $"'UseBlazorLiveReloading' to 'false' in your project file." +
+                        $"\nThe exception was: {ex.Message}\n{ex.StackTrace}");
+                }
+            }
+
+            return VSConstants.S_OK;
+        }
+
+        private void AttemptLogError(string message)
+        {
+            ThreadHelper.ThrowIfNotOnUIThread();
+            var outputWindow = (IVsOutputWindow)Package.GetGlobalService(typeof(SVsOutputWindow));
+            if (outputWindow != null)
+            {
+                outputWindow.GetPane(VSConstants.OutputWindowPaneGuid.BuildOutputPane_guid, out var pane);
+                if (pane != null)
+                {
+                    pane.OutputString(message);
+                    pane.Activate();
+                }
+            }
+        }
+
+        public int UpdateSolution_StartUpdate(ref int pfCancelUpdate)
+            => VSConstants.S_OK;
+
+        public int UpdateSolution_Cancel()
+            => VSConstants.S_OK;
+
+        public int OnActiveProjectCfgChange(IVsHierarchy pIVsHierarchy)
+            => VSConstants.S_OK;
+
+        public int UpdateProjectCfg_Begin(IVsHierarchy pHierProj, IVsCfg pCfgProj, IVsCfg pCfgSln, uint dwAction, ref int pfCancel)
+            => VSConstants.S_OK;
+
+        public int UpdateProjectCfg_Done(IVsHierarchy pHierProj, IVsCfg pCfgProj, IVsCfg pCfgSln, uint dwAction, int fSuccess, int fCancel)
+        {
+            if (_isListeningForProjectBuilds
+                && fSuccess == 1 // i.e., build succeeded
+                && pHierProj.IsCapabilityMatch(BlazorProjectCapability))
+            {
+                var configuredProject = ((IVsBrowseObjectContext)pCfgProj).ConfiguredProject;
+                var projectLockService = configuredProject
+                    .UnconfiguredProject
+                    .ProjectService
+                    .Services
+                    .ProjectLockService;
+
+                ThreadHelper.JoinableTaskFactory.Run(async delegate
+                {
+                    using (var access = await projectLockService.ReadLockAsync())
+                    {
+                        var project = await access.GetProjectAsync(configuredProject);
+
+                        // Now we can evaluate MSBuild properties
+                        var signalFileFullPath = project.GetPropertyValue("_BlazorBuildCompletedSignalFullPath");
+                        if (!string.IsNullOrEmpty(signalFileFullPath))
+                        {
+                            _signalFilePathsToNotify.Add(signalFileFullPath);
+                        }
+                    }
+                });
+            }
+
+            return VSConstants.S_OK;
+        }
+    }
+}

tooling/Microsoft.VisualStudio.BlazorExtension/Microsoft.VisualStudio.BlazorExtension.csproj

@@ -275,6 +275,7 @@
   <ItemGroup>
     <Compile Include="AboutDialogInfoAttribute.cs" />
     <Compile Include="BlazorPackage.cs" />
+    <Compile Include="LiveReloadBuildWatcher.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
   </ItemGroup>
   <ItemGroup>