C# &引用；InvalidOperationException:类型为'；的服务不可用；Microsoft.Extensions.Configuration.IConfiguration'；已注册。”；

我对编程有点陌生，对c#和.NET内核也很陌生

我很难确定为什么这个简单的“hello world”应用程序会因为标题中的错误而失败

我试图让应用程序读取appsettings.json中的“Hello！！”并将其显示在屏幕上

这是我的Startup.cs

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Configuration;

namespace My_NET_Core_Test_2
{
    public class Startup
    {
        // This method gets called by the runtime. Use this method to add services to the container.
        // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
        public void ConfigureServices(IServiceCollection services)
        {
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, 
                                IHostingEnvironment env, 
                                ILoggerFactory loggerFactory,
                                IConfiguration configuration)
        {
            loggerFactory.AddConsole();

            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }

            app.Run(async (context) =>
            {
                var greeting = configuration["Greeting"];
                await context.Response.WriteAsync(greeting);
            });
        }
    }
}

这是我的程序。cs：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Hosting;

namespace My_NET_Core_Test_2
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var host = new WebHostBuilder()
                .UseKestrel()
                .UseContentRoot(Directory.GetCurrentDirectory())
                .UseIISIntegration()
                .UseStartup<Startup>()
                .UseApplicationInsights()
                .Build();

            host.Run();
        }
    }
}

---

我感谢你的帮助

此问题可能是因为无法解决IConfiguration实例。您可以通过在启动构造函数中定义实例，让我们定义从何处获取配置值

下面是一个基本示例，其中ConfigurationBuilder将从内容根路径中的appsettings.json读取值，并读取环境变量

public class Startup
{
    private readonly IConfiguration _configuration;

    public Startup(IHostingEnvironment env)
    {
        var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile($"appsettings.json", optional: false, reloadOnChange: true)
                .AddEnvironmentVariables();
        _configuration = builder.Build();
    }

    // This method gets called by the runtime. Use this method to add services to the container.
    // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
    public void ConfigureServices(IServiceCollection services)
    {
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, 
                            IHostingEnvironment env, 
                            ILoggerFactory loggerFactory)
    {
        loggerFactory.AddConsole();

        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.Run(async (context) =>
        {
            var greeting = _configuration["Greeting"];
            await context.Response.WriteAsync(greeting);
        });
    }
}

---

也许我遗漏了什么，但是您在哪里注册

IConfiguration

的实现呢？看一看，看起来您使用的是旧版本的ASP.NET Core（如果不是，则使用的是旧方法）。您实际使用的是哪个版本？您的项目版本是什么？我在.net core 2.1下对您的代码进行了测试，我只需要通过`var host=new WebHostBuilder（）.UseKestrel（）.UseContentRoot（Directory.GetCurrentDirectory（））.ConfigureAppConfiguration（（hostingContext，config）=>{config.AddJsonFile（“appsettings.json”，可选：false，reloadOnChange:false）；}）.UseIISIntegration（）.UseStartup（）.Build（）；`Hmm.我已经尝试将项目的目标框架设置为.NET Core 2.1（在使用1.1之前），我得到了相同的结果。当我尝试更新我的Program.cs Main方法以使用Tao Zhou建议的代码时，Visual Studio似乎不喜欢ConfigureAppConfiguration行。“IWebHostBuilder不包含…的定义。”

public class Startup
{
    private readonly IConfiguration _configuration;

    public Startup(IHostingEnvironment env)
    {
        var builder = new ConfigurationBuilder()
                .SetBasePath(env.ContentRootPath)
                .AddJsonFile($"appsettings.json", optional: false, reloadOnChange: true)
                .AddEnvironmentVariables();
        _configuration = builder.Build();
    }

    // This method gets called by the runtime. Use this method to add services to the container.
    // For more information on how to configure your application, visit https://go.microsoft.com/fwlink/?LinkID=398940
    public void ConfigureServices(IServiceCollection services)
    {
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, 
                            IHostingEnvironment env, 
                            ILoggerFactory loggerFactory)
    {
        loggerFactory.AddConsole();

        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        app.Run(async (context) =>
        {
            var greeting = _configuration["Greeting"];
            await context.Response.WriteAsync(greeting);
        });
    }
}