In BlazorWebView WinForms/WPF, don't require wwwroot to exist in bin directory in development

Fixes #4537

Author: SteveSandersonMS

src/BlazorWebView/samples/BlazorWinFormsApp/BlazorWinFormsApp.csproj

@@ -15,12 +15,6 @@
     <ProjectReference Include="..\WebViewAppShared\WebViewAppShared.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Content Update="wwwroot\**">
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-    </Content>
-  </ItemGroup>
-
   <Import Project="..\..\src\WindowsForms\build\Microsoft.AspNetCore.Components.WebView.WindowsForms.targets" />
 
 </Project>

src/BlazorWebView/samples/BlazorWpfApp/BlazorWpfApp.csproj

@@ -15,12 +15,6 @@
     <ProjectReference Include="..\WebViewAppShared\WebViewAppShared.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Content Update="wwwroot\**">
-      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
-    </Content>
-  </ItemGroup>
-
   <Import Project="..\..\src\Wpf\build\Microsoft.AspNetCore.Components.WebView.Wpf.targets" />
 
 </Project>

src/BlazorWebView/src/WindowsForms/BlazorWebView.cs

@@ -198,7 +198,17 @@ private void HandleRootComponentsCollectionChanged(object sender, NotifyCollecti
 		/// <returns>Returns a <see cref="IFileProvider"/> for static assets.</returns>
 		public virtual IFileProvider CreateFileProvider(string contentRootDir)
 		{
-			return new PhysicalFileProvider(contentRootDir);
+			if (Directory.Exists(contentRootDir))
+			{
+				// Typical case after publishing, or if you're copying content to the bin dir in development for some nonstandard reason
+				return new PhysicalFileProvider(contentRootDir);
+			}
+			else
+			{
+				// Typical case in development, as the files come from Microsoft.AspNetCore.Components.WebView.StaticContentProvider
+				// instead and aren't copied to the bin dir
+				return new NullFileProvider();
+			}
 		}
 
 		/// <inheritdoc />

src/BlazorWebView/src/Wpf/BlazorWebView.cs

@@ -218,7 +218,17 @@ private void HandleRootComponentsCollectionChanged(object sender, NotifyCollecti
 		/// <returns>Returns a <see cref="IFileProvider"/> for static assets.</returns>
 		public virtual IFileProvider CreateFileProvider(string contentRootDir)
 		{
-			return new PhysicalFileProvider(contentRootDir);
+			if (Directory.Exists(contentRootDir))
+			{
+				// Typical case after publishing, or if you're copying content to the bin dir in development for some nonstandard reason
+				return new PhysicalFileProvider(contentRootDir);
+			}
+			else
+			{
+				// Typical case in development, as the files come from Microsoft.AspNetCore.Components.WebView.StaticContentProvider
+				// instead and aren't copied to the bin dir
+				return new NullFileProvider();
+			}
 		}
 
 		private void CheckDisposed()