打开后缀为.csproj文件(如果使用vs,右键项目-编辑项目文件)，迁移之前的代码。
根据官方文档添加的包
<FrameworkReference Include="Microsoft.AspNetCore.App" /> <PackageReference Include="Microsoft.AspNetCore.Diagnostics.EntityFrameworkCore" Version="3.1.0" /> <PackageReference Include="Microsoft.AspNetCore.Identity.EntityFrameworkCore" Version="3.1.0" /> <PackageReference Include="Microsoft.AspNetCore.Identity.UI" Version="3.1.0" /> <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="3.1.0" /> <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="3.1.0" /> <PackageReference Include="Microsoft.AspNetCore.Mvc.NewtonsoftJson" Version="3.1.0" /> <PackageReference Include="Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation" Version="3.1.0" Condition="‘$(Configuration)‘ == ‘Debug‘" />
修改后
右键项目重新生成，出现了一个错误，经过查找资料，我把<FrameworkReference Include="Microsoft.AspNetCore.App" />这个包去掉了，就解决了。
修改Program.cs
修改Startup.cs
using Microsoft.Extensions.Hosting;
#删除 public void ConfigureServices(IServiceCollection services) { services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); } public void Configure(IApplicationBuilder app, IHostingEnvironment env) { app.UseMvc(routes => { routes.MapRoute( name: "default", template: "{controller=Home}/{action=Index}/{id?}"); }); } #添加 public void ConfigureServices(IServiceCollection services) { services.AddControllersWithViews(); } public void Configure(IApplicationBuilder app, IWebHostEnvironment env) { app.UseRouting(); app.UseAuthorization(); app.UseEndpoints(endpoints => { endpoints.MapControllerRoute( name: "default", pattern: "{controller=Home}/{action=Index}/{id?}"); }); }
重新生成项目，生成文件成功。
原文：https://www.cnblogs.com/-zzc/p/14828777.html