why this error generated on blazor and how to solve it ?

Question

why this error generated on blazor and how to solve it ?

Ahmed Salah Abed Elaziz 390

I work on blazor app server side . i found my app stuck i don't kno why it stuck i trace event viewer to check it i found exception below

Category: Microsoft.AspNetCore.Components.Server.Circuits.CircuitHost
EventId: 111
SpanId: b5f359c71bdf98dd
TraceId: 55c402b51115a74fe957d0762f8e004f
ParentId: 0000000000000000
RequestId: 800002a3-0000-f500-b63f-84710c7967bb
RequestPath: /_blazor
TransportConnectionId: GD0qeN4kpoisoFqdq7Lm_Q

Unhandled exception in circuit 'fsJjR_i80e4-G8BcnIas7mkmnqTlTY5vpTXVNEzo_Rg'.

Exception: 
System.NullReferenceException: Object reference not set to an instance of an object.
   at UC.AppRepository.UI.Startup.<>c.<ConfigureServices>b__4_1(IServiceProvider _) in D:\test repository\BackupBlazor\UC.AppRepository.UI\Startup.cs:line 67
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitCache(ServiceCallSite callSite, RuntimeResolverContext context, ServiceProviderEngineScope serviceProviderEngine, RuntimeResolverLock lockType)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScopeCache(ServiceCallSite callSite, RuntimeResolverContext context)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteVisitor`2.VisitCallSite(ServiceCallSite callSite, TArgument argument)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.Resolve(ServiceCallSite callSite, ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.DynamicServiceProviderEngine.<>c__DisplayClass2_0.<RealizeService>b__0(ServiceProviderEngineScope scope)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.GetService(Type serviceType, ServiceProviderEngineScope serviceProviderEngineScope)
   at Microsoft.AspNetCore.Components.ComponentFactory.<>c__DisplayClass7_0.<CreateInitializer>g__Initialize|1(IServiceProvider serviceProvider, IComponent component)
   at Microsoft.AspNetCore.Components.ComponentFactory.PerformPropertyInjection(IServiceProvider serviceProvider, IComponent instance)
   at Microsoft.AspNetCore.Components.ComponentFactory.InstantiateComponent(IServiceProvider serviceProvider, Type componentType)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.InstantiateChildComponentOnFrame(RenderTreeFrame& frame, Int32 parentComponentId)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InitializeNewComponentFrame(DiffContext& diffContext, Int32 frameIndex)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InitializeNewSubtree(DiffContext& diffContext, Int32 frameIndex)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InsertNewFrame(DiffContext& diffContext, Int32 newFrameIndex)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.AppendDiffEntriesForRange(DiffContext& diffContext, Int32 oldStartIndex, Int32 oldEndIndexExcl, Int32 newStartIndex, Int32 newEndIndexExcl)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.ComputeDiff(Renderer renderer, RenderBatchBuilder batchBuilder, Int32 componentId, ArrayRange`1 oldTree, ArrayRange`1 newTree)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment, Exception& renderFragmentException)
   at Microsoft.AspNetCore.Components.RenderTree.Renderer.ProcessRenderQueue()

Viorel 122.6K Reputation points

2023-04-24T14:33:34.84+00:00

Did you analyze the line 67 of Startup.cs, and the preceding code?

Ahmed Salah Abed Elaziz 390

I added all details as below please help me

 <link href="/assets/css/nucleo-icons.css" rel="stylesheet" />
    <link href="/assets/css/nucleo-svg.css" rel="stylesheet" />

line 67 on startup
     services.AddScoped<ISession>(_ =>

_.GetRequiredService<IHttpContextAccessor>().HttpContext.Session);

details 
I apply session timeout after 20 minutes
so i do as below 

function checkSessionTimeout(currentUrl) {
    var sessionTimeout = 20 * 60 * 1000; // 2 minutes in milliseconds
    var lastActivity = new Date(Date.parse(sessionStorage.getItem("LastActivity"))); // get the last activity time from the client-side session
    //console.log("current date" + Date());
    //console.log("last date store" + lastActivity);
    if (new Date() - lastActivity > sessionTimeout) {
        /*console.log("reach 2 minutes")*/

sessionStorage.clear(); // clear the session storage

// window.location.href = '/login?returnUrl=' + encodeURIComponent(currentUrl); // redirect to login page with return URL window.location.href = '/Login/Login'
} else {

setTimeout(function () { checkSessionTimeout(currentUrl); }, 1000); // check again in 1 second

}

}

checkSessionTimeout(window.location.href);
2- on page.razor
protected override void OnInitialized()
{
DateTime now = DateTime.Now;
string nowString = now.ToString("yyyy-MM-ddTHH:mm:ss");
JS.InvokeVoidAsync("sessionStorage.setItem", "LastActivity", now);

}
3-after component load
protected override async Task OnAfterRenderAsync(bool firstRender)
{

var lastActivity = Session.GetInt32("LastActivity");

if ( TimeSpan.FromTicks(DateTime.Now.Ticks - lastActivity.Value) < TimeSpan.FromMinutes(20))
{
    navigationManager.NavigateTo("/Login/Login");
    return;
}

   }
4-on_host file
on last line on body 
i do the following
<script src="~/assets/js/checksessiontimeout.js"></script>
5-on startup class

public void ConfigureServices(IServiceCollection services)
        {

    services.AddHttpContextAccessor();
    services.AddHttpClient();
    services.AddRazorPages();
    services.AddServerSideBlazor();
    services.AddSession();
    services.AddSession(options =>
    {
        options.IdleTimeout = TimeSpan.FromMinutes(20);
    });

services.AddScoped<ISession>(_ => _.GetRequiredService<IHttpContextAccessor>().HttpContext.Session); }

AgaveJoe 30,126 Reputation points

2023-04-24T15:38:48.7166667+00:00

You really really need to make an effort to read the docs rather than guessing. Avoid IHttpContextAccessor/HttpContext in Razor components
Anonymous

2023-04-25T02:30:44.9266667+00:00
Hi @Ahmed Salah Abed Elaziz

Exception: System.NullReferenceException: Object reference not set to an instance of an object. at UC.AppRepository.UI.Startup.<>c.<ConfigureServices>b__4_1(IServiceProvider _) in D:\test repository\BackupBlazor\UC.AppRepository.UI\Startup.cs:line 67

From the error message, we can see the error happens in startup.cs file and line 67, so as Viorel said, you need to analyze the line 67 and preceding code of Startup.cs, and check which object is null, then change the related code and fix it.
Ahmed Salah Abed Elaziz 390 Reputation points

2023-04-25T06:05:21.48+00:00

so if is null how to check it please
AgaveJoe 30,126 Reputation points

2023-04-25T10:52:03.8466667+00:00

@Ahmed Salah Abed Elaziz, if you read link I provided you would have figured out that Blazor does have an HttpContext! It uses SignalR. Also, the code you provided returns an unassigned variable. This syntax is used when you don't care about the return type. What's the reasoning behind the using the C# discards this way?

At some point, you need to stop guessing how Blazor Server works and learn how Blazor Server works.
Anonymous

2023-04-27T07:04:17.4733333+00:00

Hi @Ahmed Salah Abed Elaziz

services.AddScoped<ISession>(_ => _.GetRequiredService<IHttpContextAccessor>().HttpContext.Session);

Can you tell us what your purpose to using the above code? And what you want to achieve? Might be we can find another workaround to achieve the same result?

Besides, about using session storage in Blazor, you can refer to this article: ASP.NET Core Blazor state management

1 answer

Your answer

Viorel 122.6K Reputation points

2023-04-24T14:33:34.84+00:00

Did you analyze the line 67 of Startup.cs, and the preceding code?
AgaveJoe 30,126 Reputation points

2023-04-24T15:38:48.7166667+00:00

You really really need to make an effort to read the docs rather than guessing. Avoid IHttpContextAccessor/HttpContext in Razor components
Anonymous

2023-04-25T02:30:44.9266667+00:00

Hi @Ahmed Salah Abed Elaziz

Exception: System.NullReferenceException: Object reference not set to an instance of an object. at UC.AppRepository.UI.Startup.<>c.<ConfigureServices>b__4_1(IServiceProvider _) in D:\test repository\BackupBlazor\UC.AppRepository.UI\Startup.cs:line 67

From the error message, we can see the error happens in startup.cs file and line 67, so as Viorel said, you need to analyze the line 67 and preceding code of Startup.cs, and check which object is null, then change the related code and fix it.
Ahmed Salah Abed Elaziz 390 Reputation points

2023-04-25T06:05:21.48+00:00

so if is null how to check it please
AgaveJoe 30,126 Reputation points

2023-04-25T10:52:03.8466667+00:00

@Ahmed Salah Abed Elaziz, if you read link I provided you would have figured out that Blazor does have an HttpContext! It uses SignalR. Also, the code you provided returns an unassigned variable. This syntax is used when you don't care about the return type. What's the reasoning behind the using the C# discards this way?

At some point, you need to stop guessing how Blazor Server works and learn how Blazor Server works.
Anonymous

2023-04-27T07:04:17.4733333+00:00

Hi @Ahmed Salah Abed Elaziz

services.AddScoped<ISession>(_ => _.GetRequiredService<IHttpContextAccessor>().HttpContext.Session);

Can you tell us what your purpose to using the above code? And what you want to achieve? Might be we can find another workaround to achieve the same result?

Besides, about using session storage in Blazor, you can refer to this article: ASP.NET Core Blazor state management

Answer 1

Bruce (SqlWork.com) 78,086 Volunteer Moderator

As a blazor server app is just one request running over signal/r, it’s not clear why you would use asp.net session. just use a service singleton.

SessionStorage is a browser feature and makes sense, as it can store data between blazor app runs and concurrent apps. (Open in two tabs)

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why this error generated on blazor and how to solve it ?

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