Blazor调用NotifyAuthenticationStateChanged后抛出异常问题排查

使用.NET 8与Chrome浏览器，运行应用后首次调用自定义AuthenticationStateProvider的AuthenticateUser方法，调用NotifyAuthenticationStateChanged后，浏览器日志出现如下异常：

blazor.web.js:1 [2023-12-07T18:37:52.343Z] Error: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
   at System.Collections.Generic.List`1.Enumerator.MoveNext()
   at Microsoft.AspNetCore.Components.CascadingValueSource`1.<>c__DisplayClass10_0.<NotifyChangedAsync>b__0()
   at Microsoft.AspNetCore.Components.Rendering.RendererSynchronizationContextDispatcher.InvokeAsync(Action workItem)
   at Microsoft.AspNetCore.Components.CascadingValueSource`1.NotifyChangedAsync()
   at Microsoft.Extensions.DependencyInjection.CascadingAuthenticationStateServiceCollectionExtensions.AuthenticationStateCascadingValueSource.HandleAuthenticationStateChanged(Task`1 newAuthStateTask)
   at PortableMemory.UI.Services.Authentication.Implementations.AppAuthenticationStateProvider.AuthenticateUser(AuthenticationModel authModel) in D:\d\PortableMemory\PortableMemory.UI\PortableMemory.UI\Services\Authentication\Implementations\AppAuthenticationStateProvider.cs:line 38
   at PortableMemory.UI.Components.Login.LoginComponent.OnSubmit() in D:\d\PortableMemory\PortableMemory.UI\PortableMemory.UI\Components\Login\LoginComponent.razor.cs:line 34
   at Microsoft.AspNetCore.Components.ComponentBase.CallStateHasChangedOnAsyncCompletion(Task task)
   at Microsoft.AspNetCore.Components.Forms.EditForm.HandleSubmitAsync()
   at Microsoft.AspNetCore.Components.ComponentBase.CallStateHasChangedOnAsyncCompletion(Task task)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.GetErrorHandledTask(Task taskToHandle, ComponentState owningComponentState)

自定义AuthenticationStateProvider实现代码：

public class AppAuthenticationStateProvider : AuthenticationStateProvider
{
    public override Task<AuthenticationState> GetAuthenticationStateAsync()
    {
        var identity = new ClaimsIdentity();
        var user = new ClaimsPrincipal(identity);

        return Task.FromResult(new AuthenticationState(user));
    }


    public void AuthenticateUser(AuthenticationModel authModel)
    {
        var identity = new ClaimsIdentity(new[]
        {
            new Claim(ClaimTypes.Name, "bob"),
        }, "Custom Authentication");

        var user = new ClaimsPrincipal(identity);

        
        NotifyAuthenticationStateChanged(
            Task.FromResult(new AuthenticationState(user)));
    }
}

这个异常的核心原因是：你在组件的同步提交流程（EditForm的OnSubmit方法）中，同步调用了NotifyAuthenticationStateChanged，触发了级联AuthenticationState的更新。此时Blazor内部正在枚举依赖该级联值的组件订阅列表，而更新过程中这个列表因为组件的重新渲染、订阅状态变更被修改，导致枚举操作与集合修改操作冲突，从而抛出"集合被修改；枚举操作可能无法执行"的异常。

简单来说，就是状态变更的时机和Blazor内部的组件枚举流程重叠，引发了集合操作的冲突。

内容的提问来源于stack exchange，提问作者Masteroxify