ASP.NET Core 3.1 跨域問題解決方式

初次用net core 3.1 開發webapi接口時遇到跨域問題，花費了點時間從網上找的資料，但是有些不全，所以下面就粘貼上解決辦法，已經測試過，沒問題的。

修改項目中的Startup類，添加紅色字體標注的代碼，注意這是ASP.NET Core 3.1 跨域解決辦法

    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)
        {
            //配置跨域處理，允許所有來源
            services.AddCors(options =>
            {
                options.AddPolicy("cors",
                    builder => builder.AllowAnyOrigin() .AllowAnyHeader() .AllowAnyMethod() ); });

            services.AddControllers();

            services.AddMvcService(); 

            //注冊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(() =>
            {
                //網站啟動完成執行            
            });
            applicationLifetime.ApplicationStopping.Register(() =>
            {
                //網站停止過程中執行          
            });
            applicationLifetime.ApplicationStopped.Register(() =>
            {
                //網站停止完成執行             
            });                       

            app.UseRouting();

            //允許所有跨域，cors是在ConfigureServices方法中配置的跨域策略名稱
            //注意：UseCors必須放在UseRouting和UseEndpoints之間
            app.UseCors("cors");

            //使用靜態文件
            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稱
                endpoints.MapControllers().RequireCors("cors");
            });

            //調用中間件
            app.UseSwaggerMiddleware();
           
        }
    }