.NET Hosting报错：Microsoft.AspNetCore.Hosting.IStartup不受支持

错误原因 #

你混用了ASP.NET Core 6+的WebApplication构建模式和旧版的Startup类模式：

• UseStartup<StartupBase>在新的WebApplication流程中已被废弃，不再支持IStartup接口，直接触发NotSupportedException。
• 代码中重复构建了两个主机实例（app和host），且同时调用app.Run()和host.Run()，导致运行时冲突。

修复方案 #

删除旧的Startup模式相关代码，将数据库迁移逻辑整合到当前的WebApplication构建流程中，具体修改如下：

修复后的完整代码 #

using System.Net;
using System.Text;
using DatingApp.API.Data;
using DatingApp.API.Helpers;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.AspNetCore.Diagnostics;
using Microsoft.EntityFrameworkCore;
using Microsoft.IdentityModel.Tokens;

namespace DatingApp.API
{
    class Program
    {
        public static void Main(string[] args)
        {
            var builder = WebApplication.CreateBuilder(args);

            // Add services to the container.
            builder.Services.AddControllers();
            builder.Services.AddEndpointsApiExplorer();
            builder.Services.AddSwaggerGen();

            builder.Services.AddDbContext<DataContext>(options =>
            {
                options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection"));
            });

            builder.Services.AddCors(x => x.AddPolicy("corsapp", builder =>
            {
                builder.AllowAnyOrigin().AllowAnyMethod().AllowAnyHeader();
            }));

            builder.Services.AddScoped<IAuthRepository, AuthRepository>();
            builder.Services.AddScoped<IDatingRepository, DatingRepository>();

            builder.Services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
                .AddJwtBearer(options =>
                {
                    options.TokenValidationParameters = new TokenValidationParameters
                    {
                        ValidateIssuerSigningKey = true,
                        IssuerSigningKey = new SymmetricSecurityKey(Encoding.UTF8
                            .GetBytes(builder.Configuration.GetSection("AppSettings:Token").Value)),
                        ValidateIssuer = false,
                        ValidateAudience = false
                    };
                });

            var app = builder.Build();

            // 执行数据库迁移和种子数据填充
            using (var scope = app.Services.CreateScope())
            {
                var services = scope.ServiceProvider;
                try
                {
                    var context = services.GetRequiredService<DataContext>();
                    context.Database.Migrate();
                    Seed.SeedUsers(context);
                }
                catch (Exception ex)
                {
                    var logger = services.GetRequiredService<ILogger<Program>>();
                    logger.LogError(ex, "迁移过程中发生错误");
                }
            }

            // Configure the HTTP request pipeline. 
            if (app.Environment.IsDevelopment())
            {
                app.UseSwagger();
                app.UseSwaggerUI();
            }
            else
            {
                app.UseExceptionHandler(builder =>
                {
                    builder.Run(async context =>
                    {
                        context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
                        var error = context.Features.Get<IExceptionHandlerFeature>();
                        if (error != null)
                        {
                            // 修正扩展方法的大小写问题
                            context.Response.AddApplicationError(error.Error.Message);
                            await context.Response.WriteAsync(error.Error.Message);
                        }
                    });
                });
            }

            // app.UseHttpsRedirection();

            app.UseRouting();

            app.UseCors("corsapp");

            app.UseAuthentication();

            app.UseAuthorization();

            app.MapControllers();

            app.Run();
        }
    }
}

额外修正点 #

1. 修正了数据库连接字符串的读取方式：将options.UseSqlServer("DefaultConnection")改为options.UseSqlServer(builder.Configuration.GetConnectionString("DefaultConnection"))，确保正确读取配置文件中的连接字符串。
2. 修正了扩展方法的拼写错误：context.Response.addApplicationError改为context.Response.AddApplicationError（符合C#命名规范）。

内容的提问来源于stack exchange，提问作者Youssef Alamrousy