【Azure Developer】使用Azure PubSub服务示例代码时候遇见了.NET 6.0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.gaodi.net/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

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