【AzureDeveloper】使用AzurePubSub服务示例代码时候遇见了.NET6.0的代码转换问题

问题描述

当本地环境中安装.NET 6.0后，用指令 dotnet new web 或  dotnet new console 生成的项目，使用的都是新模板生成的Program.cs文件。里面去掉了namespace， class 以及main函数的定义。使得代码更简洁。

生成的 Program.cs 代码为：

var builder = WebApplication.CreateBuilder(args);var app = builder.Build();app.MapGet("/", () => "Hello World!");app.Run();

与示例代码中所使用的代码结构差距十分巨大(示例链接：https://docs.microsoft.com/en-us/azure/azure-web-pubsub/tutorial-subprotocol?tabs=csharp)：

using Azure.Messaging.WebPubSub;using Microsoft.AspNetCore.Builder;using Microsoft.AspNetCore.Hosting;using Microsoft.AspNetCore.Http;using Microsoft.Extensions.Azure;using Microsoft.Extensions.Configuration;using Microsoft.Extensions.DependencyInjection;using Microsoft.Extensions.Hosting;namespace logstream{    public class Startup    {        public Startup(IConfiguration configuration)        {            Configuration = configuration;        }        public IConfiguration Configuration { get; }        public void ConfigureServices(IServiceCollection services)        {            services.AddAzureClients(builder =>            {                builder.AddWebPubSubServiceClient(Configuration["Azure:WebPubSub:ConnectionString"], "stream");            });        }        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)        {            if (env.IsDevelopment())            {                app.UseDeveloperExceptionPage();            }            app.UseStaticFiles();            app.UseRouting();            app.UseEndpoints(endpoints =>            {                endpoints.MapGet("/negotiate", async context =>                {                    var service = context.RequestServices.GetRequiredService<WebPubSubServiceClient>();                    var response = new                    {                        url = service.GetClientAccessUri(roles: new string[] { "webpubsub.sendToGroup.stream", "webpubsub.joinLeaveGroup.stream" }).AbsoluteUri                    };                    await context.Response.WriteAsJsonAsync(response);                });            });        }    }}

那么如何来定义 ConfigureServices， 如何来 Configure 中的代码呢？如何来解决 CS8803 : Top-level statements must precede namespace and type declarations

 

问题分析

这是代码由.NET 5.0 到 .NET 6.0的升级转换问题。

在.NET 6 之前，每一个应用程序都将应用的初始化代码拆分放在 Program.cs 和 Startup.cs 文件中。他们是两个独立的类，而在.NET 6.0中，为了简洁，为了最小化API，把两个类进行了合并。生成新的Program.cs中去掉了命名空间(Namespace, Class定义， Main函数)。使得在启动一个应用时，代码达到最少。 （PS:C# 编译器会自动生成Mian函数)

 

在查看官方对于5.0 变为 6.0的文档介绍：https://docs.microsoft.com/en-us/aspnet/core/migration/50-to-60?view=aspnetcore-6.0&tabs=visual-studio

1. ConfigureServices 函数里面的 services.AddXXXXX()等都可以转换为  builder.Services.AddXXXXX()
2. Configure 函数中的内容，可以直接写在 var app = builder.Build(); 代码之后。

所以，本文之前的代码，可以直接转换为：

using Azure.Messaging.WebPubSub;using Microsoft.AspNetCore.Builder;using Microsoft.AspNetCore.Hosting;using Microsoft.AspNetCore.Http;using Microsoft.Extensions.Azure;using Microsoft.Extensions.Configuration;using Microsoft.Extensions.DependencyInjection;using Microsoft.Extensions.Hosting;var ConnectionString = "";var builder = WebApplication.CreateBuilder(args);builder.Services.AddAzureClients(builder =>{    builder.AddWebPubSubServiceClient(ConnectionString, "stream");});var app = builder.Build();if (!app.Environment.IsDevelopment()){    app.UseDeveloperExceptionPage();}app.UseStaticFiles();app.UseRouting();app.UseEndpoints(endpoints =>{    endpoints.MapGet("/negotiate", async context =>    {        var service = context.RequestServices.GetRequiredService<WebPubSubServiceClient>();        var response = new        {            url = service.GetClientAccessUri(roles: new string[] { "webpubsub.sendToGroup.stream", "webpubsub.joinLeaveGroup.stream" }).AbsoluteUri        };        await context.Response.WriteAsJsonAsync(response);    });});app.MapGet("/", () => "Hello World!");app.Run();

 

 

 

特别注意，在新模板下的代码，非常容易出现：CS8803 : Top-level statements must precede namespace and type declarations 错误。这是因为 .NET 6.0在隐藏了Main函数后，在编译代码时候，会自动补上Main函数，所以在Program.cs 的代码中，如果需要定义其他类，必须放在文件的末尾，不能在文件开头部分和中间。

当Class定义代码放在Program.cs开头部分

当Class定义代码放在Program.cs中间部分

当Class定义代码放在Program.cs结尾部分

更多关于Top-level statements的说明，请见：https://www.cnblogs.com/lulight/articles/16285885.html

 

参考资料

Tutorial: Publish and subscribe messages between WebSocket clients using subprotocol: https://docs.microsoft.com/en-us/azure/azure-web-pubsub/tutorial-subprotocol?tabs=csharp

 

Migrate from ASP.NET Core 5.0 to 6.0：https://docs.microsoft.com/en-us/aspnet/core/migration/50-to-60?view=aspnetcore-6.0&tabs=visual-studio

 

C# 9.0 - Introduction To Top-Level Statements ：https://www.c-sharpcorner.com/article/c-sharp-9-0-top-level-statement/#:~:text=Top%20Level%20statements%20should%20be%20first%20before%20any,Top-level%20Statements.%20That%E2%80%99s%20all%20for%20the%20Top-level%20statement.

 

Migrate from ASP.NET Core 5.0 to 6.0