Blazor中IHttpContextAccessor注入后为空的问题求助

核心问题 #

你在CustomStateProvider中使用[Inject]属性注入IHttpContextAccessor，但服务类（非Blazor组件）的依赖注入必须通过构造函数实现，[Inject]属性仅适用于Blazor组件类，这是导致属性为空的直接原因。

修改步骤 #

1. 重构CustomStateProvider的注入方式

移除[Inject]属性，将IHttpContextAccessor通过构造函数注入：

public class CustomStateProvider : AuthenticationStateProvider
{
    private readonly IHttpContextAccessor _httpContextAccessor;
    private readonly IAuthService _authService;
    private CurrentUser _currentUser;

    // 通过构造函数注入两个依赖
    public CustomStateProvider(IAuthService authService, IHttpContextAccessor httpContextAccessor)
    {
        _authService = authService;
        _httpContextAccessor = httpContextAccessor;
    }

    public override async Task<AuthenticationState> GetAuthenticationStateAsync()
    {
        var identity = new ClaimsIdentity();
        try
        {
            var userInfo = GetCurrentUser();
            if (userInfo.IsAuthenticated)
            {
                var claims = new[] { new Claim(ClaimTypes.Name, _currentUser.UserName) }
                               .Concat(_currentUser.Claims.Select(c => new Claim(c.Key, c.Value)));
                identity = new ClaimsIdentity(claims, "Server authentication");
            }
        }
        catch (HttpRequestException ex)
        {
            Console.WriteLine("Request failed:" + ex);
        }

        return new AuthenticationState(new ClaimsPrincipal(identity));
    }

    public async Task Login(ConnexionModel loginParameters)
    {
        _authService.Login(loginParameters);

        var user = _authService.GetUser(loginParameters.UserName);
        _currentUser = user;
        var cookieOptions = new CookieOptions
        {
            Expires = DateTime.Now.AddDays(7),
            HttpOnly = true
        };
        _httpContextAccessor.HttpContext.Response.Cookies.Append("CurrentUser", JsonConvert.SerializeObject(_currentUser), cookieOptions);
        NotifyAuthenticationStateChanged(GetAuthenticationStateAsync());
    }

    public async Task Logout()
    {
        _currentUser = null;
        _httpContextAccessor.HttpContext.Response.Cookies.Delete("CurrentUser");
        NotifyAuthenticationStateChanged(GetAuthenticationStateAsync());
    }

    public async Task Register(InscriptionModel registerParameters)
    {
        _authService.Register(registerParameters);

        var user = _authService.GetUser(registerParameters.UserName);
        _currentUser = user;
        var cookieOptions = new CookieOptions
        {
            Expires = DateTime.Now.AddDays(7),
            HttpOnly = true
        };
        _httpContextAccessor.HttpContext.Response.Cookies.Append("CurrentUser", JsonConvert.SerializeObject(_currentUser), cookieOptions);
        NotifyAuthenticationStateChanged(GetAuthenticationStateAsync());
    }

    public CurrentUser GetCurrentUser()
    {
        if (_currentUser != null && _currentUser.IsAuthenticated)
        {
            return _currentUser;
        }
        else
        {
            var cookie = _httpContextAccessor.HttpContext.Request.Cookies["CurrentUser"];
            if (cookie != null)
            {
                return JsonConvert.DeserializeObject<CurrentUser>(cookie);
            }
        }

        return new CurrentUser();
    }
}

2. 确认Program.cs的服务注册（你的配置无需修改）

当前的服务注册逻辑是正确的，保持顺序即可：

builder.Services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
builder.Services.AddScoped<CustomStateProvider>();
builder.Services.AddScoped<AuthenticationStateProvider>(s => s.GetRequiredService<CustomStateProvider>());

额外注意事项 #

• 若你使用的是Blazor WebAssembly，IHttpContextAccessor本身不可用，因为WebAssembly运行在浏览器环境中，没有服务器端的HttpContext，此时需改用浏览器本地存储（如localStorage）保存用户信息。
• 在Blazor Server中，HttpContext仅在初始请求或SignalR交互的上下文内可用，若在后台线程中调用GetAuthenticationStateAsync，可能会出现HttpContext为空的情况，建议将用户信息缓存到服务内部，减少对HttpContext的直接依赖。

内容的提问来源于stack exchange，提问作者Armure