Endpoint Routing does not support 'IApplicationBuilder.UseMvc(...)'. To use 'IApplicationBuilder.UseMvc'...'

.Net Core 更新太快了，上一个版本用 useMVC() 或 app.UseMvcWithDefaultRoute() 用的好好的，下一个版本就废了。这不，添加了两行

useMVC()
app.UseMvcWithDefaultRoute()

就暴了下面的错误

Message "Endpoint Routing does not support 'IApplicationBuilder.UseMvc(...)'. To use 'IApplicationBuilder.UseMvc' set 'MvcOptions.EnableEndpointRouting = false' inside 'ConfigureServices(...)."   string

和下面两个警告

Startup.cs(13,13): Warning MVC1005: Using 'UseMvc' to configure MVC is not supported while using Endpoint Routing. To continue using 'UseMvc', please set 'MvcOptions.EnableEndpointRouting = false' inside 'ConfigureServices'. (MVC1005) (Demo)

Startup.cs(13,13): Warning MVC1005: Using 'UseMvcWithDefaultRoute' to configure MVC is not supported while using Endpoint Routing. To continue using 'UseMvcWithDefaultRoute', please set 'MvcOptions.EnableEndpointRouting = false' inside 'ConfigureServices'. (MVC1005) (Demo)

出现这个问题的原因，是 Asp.Net Core 3.0中默认不再支持app.UserMvc() 方式配置路由系统。

解决方法也简单，就是将

services.AddMvc();

改成

services.AddMvc(options => { options.EnableEndpointRouting = false; });

当然了，这不是推荐的做法，因为这么做会把 EndpointRouting 给干掉。

更推荐的做法就是

app.UseEndpoints(endpoints =>
{
    // 添加默认的路由控制器
    endpoints.MapControllerRoute(name: "default",pattern: "{controller=Home}/{action=Index}/{id?}");
});