ASP.NET Core 3.1 跨域问题解决方式

初次用net core 3.1 开发webapi接口时遇到跨域问题，花费了点时间从网上找的资料，但是有些不全，所以下面就粘贴上解决办法，已经测试过，没问题的。

修改项目中的Startup类，添加红色字体标注的代码，注意这是ASP.NET Core 3.1 跨域解决办法

    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;                
        }

        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)
        {
            //配置跨域处理，允许所有来源
            services.AddCors(options =>
            {
                options.AddPolicy("cors",
                    builder => builder.AllowAnyOrigin()
                    .AllowAnyHeader()
                    .AllowAnyMethod()
                );
            });

            services.AddControllers();

            services.AddMvcService(); 

            //注册Swagger生成器
            services.AddSwaggerService();       
   
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IHostApplicationLifetime applicationLifetime)
        {           
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }          
         
            applicationLifetime.ApplicationStarted.Register(() =>
            {
                //网站启动完成执行            
            });
            applicationLifetime.ApplicationStopping.Register(() =>
            {
                //网站停止过程中执行          
            });
            applicationLifetime.ApplicationStopped.Register(() =>
            {
                //网站停止完成执行             
            });                       

            app.UseRouting();

            //允许所有跨域，cors是在ConfigureServices方法中配置的跨域策略名称
            //注意：UseCors必须放在UseRouting和UseEndpoints之间
            app.UseCors("cors");

            //使用静态文件
            app.UseStaticFiles();

            app.UseAuthorization(); 

            app.UseEndpoints(endpoints =>
            {
                //跨域需添加RequireCors方法，cors是在ConfigureServices方法中配置的跨域策略名称
                endpoints.MapControllers().RequireCors("cors");
            });

            //调用中间件
            app.UseSwaggerMiddleware();
           
        }
    }