Blazor .NET 8登录页HttpContext返回Null的问题求助

问题背景 #

上周开发Blazor Web App .NET 8项目时登录功能正常，现在返回项目后登录页面抛出空引用异常，报错指向HttpContext为null。

Login.razor代码 #

@page "/Account/Login"
@layout EmptyLayout
@attribute [AllowAnonymous]

@using System.ComponentModel.DataAnnotations
@using AVAZicht.Components.Layout
@using Microsoft.AspNetCore.Authentication
@using Microsoft.AspNetCore.Identity
@using AVAZicht.Data

@inject SignInManager<ApplicationUser> SignInManager
@inject ILogger<Login> Logger
@inject NavigationManager NavigationManager
@inject IdentityRedirectManager RedirectManager

<PageTitle>Log in</PageTitle>

<div class="container">
    <div class="row justify-content-md-center align-items-center vh-100">
        <div class="col-lg-4" align="center">

            <img src="images/ava_logo_transp.png" class="w-75 mb-3" />

            <section class="p-0">
                <StatusMessage Message="@errorMessage" />
                <EditForm Model="Input" method="post" OnValidSubmit="LoginUser" FormName="login">
                    <DataAnnotationsValidator />
                    <ValidationSummary class="text-danger" role="alert" />
                    <div class="form-floating mb-3">
                        <InputText @bind-Value="Input.Email" class="form-control" autocomplete="username" aria-required="true" placeholder="name@example.com" />
                        <label for="email" class="form-label">Email</label>
                        <ValidationMessage For="() => Input.Email" class="text-danger" />
                    </div>
                    <div class="form-floating mb-3">
                        <InputText type="password" @bind-Value="Input.Password" class="form-control" autocomplete="current-password" aria-required="true" placeholder="password" />
                        <label for="password" class="form-label">Password</label>
                        <ValidationMessage For="() => Input.Password" class="text-danger" />
                    </div>
                    <div class="checkbox mb-3">
                        <label class="form-label">
                            <InputCheckbox @bind-Value="Input.RememberMe" class="darker-border-checkbox form-check-input" />
                            Ingelogd blijven
                        </label>
                    </div>
                    <div>
                        <button type="submit" class="w-100 btn btn-lg btn-primary">Inloggen</button>
                    </div>
                </EditForm>
            </section>
        </div>
    </div>
</div>

@code {
    private string? errorMessage;

    [CascadingParameter]
    private HttpContext HttpContext { get; set; } = default!;

    [SupplyParameterFromForm]
    private InputModel Input { get; set; } = new();

    [SupplyParameterFromQuery]
    private string? ReturnUrl { get; set; }

    protected override async Task OnInitializedAsync()
    {
        if (HttpMethods.IsGet(HttpContext.Request.Method))
        {
            // Clear the existing external cookie to ensure a clean login process
            await HttpContext.SignOutAsync(IdentityConstants.ExternalScheme);
        }

    }

    public async Task LoginUser()
    {
        // This doesn't count login failures towards account lockout
        // To enable password failures to trigger account lockout, set lockoutOnFailure: true
        var result = await SignInManager.PasswordSignInAsync(Input.Email, Input.Password, Input.RememberMe, lockoutOnFailure: false);
        if (result.Succeeded)
        {
            Logger.LogInformation("User logged in.");
            RedirectManager.RedirectTo(ReturnUrl);
        }
        else if (result.RequiresTwoFactor)
        {
            RedirectManager.RedirectTo(
                "Account/LoginWith2fa",
                new() { ["returnUrl"] = ReturnUrl, ["rememberMe"] = Input.RememberMe });
        }
        else if (result.IsLockedOut)
        {
            Logger.LogWarning("User account locked out.");
            RedirectManager.RedirectTo("Account/Lockout");
        }
        else
        {
            errorMessage = "Error: Invalid login attempt.";
        }
    }

    private sealed class InputModel
    {
        [Required]
        [EmailAddress]
        public string Email { get; set; } = "";

        [Required]
        [DataType(DataType.Password)]
        public string Password { get; set; } = "";

        [Display(Name = "Remember me?")]
        public bool RememberMe { get; set; }
    }
}

报错信息 #

System.NullReferenceException: 'Object reference not set to an instance of an object.'

AVAZicht.Components.Account.Pages.Login.HttpContext.get returned null.

排查思路 #

• 检查组件渲染模式：HttpContext仅能在服务器渲染模式（SSR）或交互式服务器组件中获取。若Login组件添加了@rendermode InteractiveWebAssembly属性，会导致HttpContext为null。对比新项目的登录页（默认SSR），移除该属性或改为InteractiveServer。
• 确认HttpContext级联传递：检查App.razor是否包含CascadingAuthenticationState，确保HttpContext能正确级联到子组件。新项目的App.razor通常会有如下结构：

  <CascadingAuthenticationState>
      <Router AppAssembly="@typeof(App).Assembly">
          <!-- 路由内容 -->
      </Router>
  </CascadingAuthenticationState>
  

  同时检查EmptyLayout布局是否阻断了级联参数传递。
• 对比认证配置：检查Program.cs中的认证服务配置，确保AddAuthentication、AddIdentity等服务正确注册，且UseAuthentication()、UseAuthorization()在UseRouting()之后、UseEndpoints()之前调用，与新项目配置保持一致。
• 清理重建项目：删除bin/obj文件夹，重启开发环境，重新生成解决方案，排除缓存导致的异常。
• 检查EmptyLayout布局：确认EmptyLayout没有设置错误的渲染模式，且没有覆盖或阻断HttpContext的级联传递。

内容的提问来源于stack exchange，提问作者Jeremy