Error when checking if HttpContextAccessor.HttpContext.Session.GetString(key_name) has value or not

Islam Youssef 21 Reputation points
2021-09-07T11:05:32.327+00:00

Hi there
I'm using VS 2019 community, in my application that using .net core MVC I'm trying to check if user signed in or not by checking the value of Session - HttpContextAccessor.HttpContext.Session.GetString(key_name) -, it is okay if user signed in, but if not he try to open a View it must redirect to home control, in my case when use try to open (https://localhost:12345/User) exception occur {System.NullReferenceException
HResult=0x80004003
Message=Object reference not set to an instance of an object.
}

here is my code in startup.cs file

    public void ConfigureServices(IServiceCollection services)  
    {              
        services.Configure<CookiePolicyOptions>(options =>  
        {  
            options.CheckConsentNeeded = context => false;  
            options.MinimumSameSitePolicy = SameSiteMode.None;  
        });  

        services.AddHttpContextAccessor();  
        // Step 1 to use session  
        services.AddDistributedMemoryCache();  
        services.AddSession(options =>  
        {  
            options.IdleTimeout = TimeSpan.FromMinutes(15);  
            options.Cookie.HttpOnly = true;  
            options.Cookie.IsEssential = true;  
        });  
          
        services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();  

        services.AddControllersWithViews();  
    }  

    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)  
    {  
        if (env.IsDevelopment())  
        {  
            app.UseDeveloperExceptionPage();  
        }  
        else  
        {  
            app.UseExceptionHandler("/Home/Error");  
            app.UseHsts();  
        }  
        app.UseHttpsRedirection();  
        app.UseStaticFiles();  

        app.UseRouting();  

        app.UseAuthentication();  
        app.UseAuthorization();  

        app.UseCookiePolicy();  
        app.UseSession();  

        app.UseEndpoints(endpoints =>  
        {  
            endpoints.MapControllerRoute(  
                name: "default",  
                pattern: "{controller=Home}/{action=Index}/{id?}"  
                //pattern: "{controller=Doc}/{action=Index}/{id?}"  
                );  
        });  
    }  

and there is my code when trying to check if session has value to continue viewing index, or navigate to another view:
var d = HttpContextAccessor.HttpContext.Session.GetString(key_UN);
if (d == null)
{
RedirectToAction("index", "Home");
}

So if there ais any advice I will appreciate that

thanks 129876-untitled.png

ASP.NET Core
ASP.NET Core
A set of technologies in the .NET Framework for building web applications and XML web services.
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  1. Adam Jachocki 46 Reputation points
    2021-09-07T14:24:09.61+00:00

    It looks like Session is empty. I mean there is no session at this point. Try:

    var d = HttpContextAccessor.HttpContext.Session?.GetString(key_UN);
    

    Notice the question mark.


  2. Islam Youssef 21 Reputation points
    2021-09-07T16:08:20.423+00:00

    Hi there (AGAIN)
    after searching and a little of luck I think I've got the solution!, it is not logic but it worked.
    I wrote startup.cs again with a different order of methods
    this my code
    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
    services.AddHttpContextAccessor();

            // Step 1 to use session  
            //services.AddDistributedMemoryCache();  
            services.AddSession(options =>  
            {  
                options.IdleTimeout = TimeSpan.FromMinutes(15);  
                options.Cookie.HttpOnly = true;  
                options.Cookie.IsEssential = true;  
                //options.Cookie.Name = ".islam.cookie";  
            });  
            services.AddMemoryCache();  
    
            services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();  
    
            services.AddControllersWithViews();  
        }  
    
        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.  
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)  
        {  
            if (env.IsDevelopment())  
            {  
                app.UseDeveloperExceptionPage();  
            }  
            else  
            {  
                app.UseExceptionHandler("/Home/Error");  
                app.UseHsts();  
            }  
            app.UseHttpsRedirection();  
            app.UseStaticFiles();  
    
            app.UseRouting();  
    
            // Step 2 to use seeion --> watch out the order           
            app.UseSession();  
              
            app.UseEndpoints(endpoints =>  
            {  
                endpoints.MapControllerRoute(  
                    name: "default",  
                    pattern: "{controller=Home}/{action=Index}/{id?}"  
                    //pattern: "{controller=Doc}/{action=Index}/{id?}"  
                    );  
            });  
        }  
    

    and this was the result when I check if session has a value or not
    129906-untitled.png

    SO thanks Adam and Bruse, I appreciate your quick help, and if there are any source to study asp.net core mvc from I will be thank full

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