Error while trying to add session to startup

Question

I have a problem, always when I will compile the solution this giving error:

System.Invalidoperationexception: 'Unable to resolve service for type 'Microsoft.AspNetCore.Session.Isessionstore' while attempting to Activate 'Microsoft.AspNetCore.Session.Sessionmiddleware'.'

Arquivo Startup.Cs

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
    services.Configure<CookiePolicyOptions>(options =>
    {
        // This lambda determines whether user consent for non-essential cookies is needed for a given request.
        options.CheckConsentNeeded = context => true;
        options.MinimumSameSitePolicy = SameSiteMode.None;
    });


    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
}

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");
        app.UseHsts();
    }

    app.UseHttpsRedirection();
    app.UseStaticFiles();
    app.UseCookiePolicy();
    app.UseSession();

    app.UseMvc(routes =>
    {
        routes.MapRoute(
            name: "default",
            template: "{controller=Home}/{action=Index}/{id?}");
    });
}

Answer 1

This is because you cannot "configure" the session without first adding it to the services. To fix it, add it to the method ConfigureServices in this way:

services.AddSession();

See more on official documentation of aspnet core.

Answer 2

It’s like the guy above said, try to put the services.Addsession();

public void ConfigureServices(IServiceCollection services)
{
    services.Configure<CookiePolicyOptions>(options =>
    {
        // This lambda determines whether user consent for non-essential cookies is needed for a given request.
        options.CheckConsentNeeded = context => true;
        options.MinimumSameSitePolicy = SameSiteMode.None;
    });

    // Este trecho aqui
    services.AddSession();

    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
}