ASP.NET托管Blazor WASM升级.NET 6后Hot Reload触发空引用异常问题

完整报错堆栈：

Error: System.NullReferenceException: Object reference not set to an instance of an object.
at Microsoft.AspNetCore.Components.WebAssembly.HotReload.WebAssemblyHotReload.ApplyHotReloadDelta(String moduleIdString, Byte[] metadataDelta, Byte[] ilDeta)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
--- End of stack trace from previous location ---
at Microsoft.JSInterop.Infrastructure.DotNetDispatcher.InvokeSynchronously(JSRuntime jsRuntime, DotNetInvocationInfo& callInfo, IDotNetObjectReference objectReference, String argsJson)
at Microsoft.JSInterop.Infrastructure.DotNetDispatcher.Invoke(JSRuntime jsRuntime, DotNetInvocationInfo& invocationInfo, String argsJson)
at Microsoft.AspNetCore.Components.WebAssembly.Services.DefaultWebAssemblyJSRuntime.InvokeDotNet(String assemblyName, String methodIdentifier, String dotNetObjectId, String argsJson)
at Object._convert_exception_for_method_call (https://localhost:44362/_framework/dotnet.6.0.0.qme34vl4fz.js:1:178709)
at Object._handle_exception_for_call (https://localhost:44362/_framework/dotnet.6.0.0.qme34vl4fz.js:1:180678)
at managed__Microsoft_AspNetCore_Components_WebAssembly__Microsoft_AspNetCore_Components_WebAssembly_Services_DefaultWebAssemblyJSRuntime_InvokeDotNet
at Object.invokeDotNetFromJS (https://localhost:44362/_framework/blazor.webassembly.js?version=32330328618b4ff08635274a6f31248c:1:42078)
at g (https://localhost:44362/_framework/blazor.webassembly.js?version=32330328618b4ff08635274a6f31248c:1:1618)
at Object.e.invokeMethod (https://localhost:44362/_framework/blazor.webassembly.js?version=32330328618b4ff08635274a6f31248c:1:2665)
at Object.St.Te._internal.applyHotReload (https://localhost:44362/_framework/blazor.webassembly.js?version=32330328618b4ff08635274a6f31248c:1:56100)
at https://localhost:44362/_framework/aspnetcore-browser-refresh.js:136:33
at Array.forEach ()
at applyBlazorDeltas (https://localhost:44362/_framework/aspnetcore-browser-refresh.js:134:12)

该问题是.NET 5升级.NET 6后配置不匹配、编译缓存残留导致的常见问题，按以下步骤排查修复：

• 统一所有依赖包版本
  检查Client、Server、Shared三个项目的全部NuGet依赖，确保所有Microsoft.AspNetCore.*、Microsoft.Components.*相关包的版本完全一致，且均为6.0.x正式版，不存在5.x版本的残留包。
• 清理全量编译缓存
  手动删除所有项目根目录下的bin、obj文件夹，删除ASP.NET Core托管Server项目的.vs隐藏文件夹，同时清理浏览器缓存，或按Ctrl+F5强制刷新页面加载最新的wasm资源。
• 校验项目配置文件
  打开Blazor WASM Client项目的.csproj文件，确认包含以下配置属性：

  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <UseBlazorWebAssembly>true</UseBlazorWebAssembly>
  </PropertyGroup>
  

  再打开Server项目的Properties/launchSettings.json，确认运行配置中包含Hot Reload相关配置：

  "profiles": {
    "http": {
      "commandName": "Project",
      "dotnetRunMessages": true,
      "launchBrowser": true,
      "applicationUrl": "http://localhost:5000",
      "environmentVariables": {
        "ASPNETCORE_ENVIRONMENT": "Development"
      },
      "hotReloadProfile": "blazorwasm"
    },
    // https配置也要添加相同的hotReloadProfile属性
  }
  

• 校验中间件配置
  确认Server项目的Program.cs在开发环境下已按正确顺序添加WebAssembly调试中间件：

  if (app.Environment.IsDevelopment())
  {
      app.UseWebAssemblyDebugging();
      // 其余开发环境专属中间件
  }
  

• 重新运行项目
  完成上述配置后，先执行dotnet restore还原依赖，再通过VS2022启动或者运行dotnet watch run即可正常使用Hot Reload功能。

内容的提问来源于stack exchange，提问作者MBeckius