从 appsettings.json 获取返回 NullReferenceException 的值：对象引用未设置到对象的实例。在 .net 核心 3 中

Question

不确定我在这里遗漏了什么，但我没有从我的 .NET Core 应用程序中的 appsettings.json 获取值。我已经阅读了几乎所有关于 appsettings.json 返回 NullReferenceException 的内容。 我知道有重复的post，但他们都没有解决问题

我知道的设置都做了，网上也看了，但还是返回null。我已经多次重构我的代码，但仍然运行到

NullReferenceException: Object reference not set to an instance of an object.

ShopAPI.Startup.ConfigureServices(IServiceCollection services) in Startup.cs+

var key = Encoding.UTF8.GetBytes(Configuration["ApplicationSettings : JWT_Secret"].ToString());

System.RuntimeMethodHandle.InvokeMethod(object target, object[] arguments, Signature sig, bool constructor, bool wrapExceptions)

Startup class:

public IConfiguration Configuration { get; }

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
      //.Get<Dictionary<string, string>>()

        services.AddOptions();
        var applicationSettings = Configuration.GetSection("AppSetting");
        services.Configure<ApplicationSettings>(applicationSettings);

        //services.AddSingleton(Configuration.GetSection("AppSettings").Get<ApplicationSettings>());

        services.AddControllers();

        services.AddDbContext<ShopDbContext>(option =>
        option.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

        services.AddIdentity<ApplicationUser,IdentityRole>()
           .AddEntityFrameworkStores<ShopDbContext>()
           .AddDefaultTokenProviders();

        services.Configure<IdentityOptions>(options => {
            options.Password.RequireDigit = false;
            options.Password.RequireUppercase = false;
            options.Password.RequireNonAlphanumeric = false;
            options.Password.RequiredLength = 6;
        });

        services.AddCors();

        //Jwt Authentication configuration

        //var key = Encoding.UTF8.GetBytes(Configuration["ApplicationSettings: JWT_Secret"].ToString());
        var key = Encoding.UTF8.GetBytes(Configuration["AppSetting : JWT_Secret"].ToString());

        services.AddAuthentication(x => {
            x.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;
            x.DefaultChallengeScheme = JwtBearerDefaults.AuthenticationScheme;
            x.DefaultScheme = JwtBearerDefaults.AuthenticationScheme;
        }).AddJwtBearer(x =>
        {
            x.RequireHttpsMetadata = false;
            x.SaveToken = false;
            x.TokenValidationParameters = new TokenValidationParameters
            {
                ValidateIssuerSigningKey = true,
                IssuerSigningKey = new SymmetricSecurityKey(key),
                ValidateIssuer = false,
                ValidateAudience = false,
                ClockSkew = TimeSpan.Zero
            };
        });
}

appsettings.json

{
  "ConnectionStrings": {
    "DefaultConnection": "Server=(localdb)\mssqllocaldb;Database=api2;Trusted_Connection=True;Connection Timeout=120;MultipleActiveResultSets=true"
  },
  "AppSetting": {
    "JWT_Secret": "1234567890123456",
    "Client_URL": "http://localhost:4500"
  },
  "AllowedHosts": "*"
}

Answer 1

我终于修正了这个错误。我认为 .net core 3 中的配置不同我实际上遵循了这个tutorial。

对于那些可能面临同样问题的人

var applicationSettings = Configuration.GetSection("AddSettings");
services.Configure<ApplicationSettings>(applicationSettings);

var appSettingsSecretKey = applicationSettings.Get<ApplicationSettings>();

然后将变量appSettingsSecretKey传给

var key = Encoding.ASCII.GetBytes(appSettingsSecretKey.JWT_Secret);

从 appsettings.json 获取返回 NullReferenceException 的值：对象引用未设置到对象的实例。在 .net 核心 3 中

Getting value from appsettings.json returning NullReferenceException: Object reference not set to an instance of an object. in .net core 3

api

startup

asp.net-core