环境变量已设置，但 HostingEnvironment.EnvironmentName 未更新

Question

我正在运行 .net core 2.2 并在 Windows 服务中托管 asp.net core。
例如。看到这个https://learn.microsoft.com/en-us/aspnet/core/host-and-deploy/windows-service?view=aspnetcore-2.2&tabs=visual-studio

我将环境变量 ASPNETCORE_ENVIRONMENT 设置为“Dev”

只是为了确认，在我的 launchsettings.json 中

  "environmentVariables": {
    "ASPNETCORE_ENVIRONMENT ": "Dev"
  }

启动时，HostingEnvironment.EnvironmentName 的值不会更新，仍为默认值“Production”。为什么不是“开发”？

public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
    WebHost.CreateDefaultBuilder(args)                
        .ConfigureLogging((hostingContext, logging) =>
        {
            logging.AddEventLog();
        })
        .ConfigureAppConfiguration((context, config) =>
        {

            // Configure the app here.
            var env = context.HostingEnvironment;
            config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                              .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);

        })
        .UseStartup<Startup>();

}

Answer 1

我花了很长时间试图找出在这种情况下最适合我做的事情。

我最终从 Microsoft.Extensions.Hosting.Host.CreateDefaultBuilder 获取代码并在构建器上添加 .UseEnvironment 扩展。

            builder.UseEnvironment(Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Development");

我默认使用“开发”而不是通常首选的“生产”，但这是个人偏好。

它是有限的，如果您想变得聪明并检查命令行参数等，请随意。这是一个起点。

public static IHostBuilder CreateDefaultBuilder(string[] args)
{
    var builder = new HostBuilder();

    // This line has been added to read the environment variable.
    builder.UseEnvironment(Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Development");

    builder.UseContentRoot(Directory.GetCurrentDirectory());
    builder.ConfigureHostConfiguration(config =>
    {
        config.AddEnvironmentVariables(prefix: "DOTNET_");
        if (args != null)
        {
            config.AddCommandLine(args);
        }
    });

    builder.ConfigureAppConfiguration((hostingContext, config) =>
    {
        var env = hostingContext.HostingEnvironment;

        config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);

        if (env.IsDevelopment() && !string.IsNullOrEmpty(env.ApplicationName))
        {
            var appAssembly = Assembly.Load(new AssemblyName(env.ApplicationName));
            if (appAssembly != null)
            {
                config.AddUserSecrets(appAssembly, optional: true);
            }
        }

        config.AddEnvironmentVariables();

        if (args != null)
        {
            config.AddCommandLine(args);
        }
    })
    .ConfigureLogging((hostingContext, logging) =>
    {
        var isWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);

        // IMPORTANT: This needs to be added *before* configuration is loaded, this lets
        // the defaults be overridden by the configuration.
        if (isWindows)
        {
            // Default the EventLogLoggerProvider to warning or above
            logging.AddFilter<EventLogLoggerProvider>(level => level >= Microsoft.Extensions.Logging.LogLevel.Warning);
        }

        logging.AddConfiguration(hostingContext.Configuration.GetSection("Logging"));
        logging.AddConsole();
        logging.AddDebug();
        logging.AddEventSourceLogger();

        if (isWindows)
        {
            // Add the EventLogLoggerProvider on windows machines
            logging.AddEventLog();
        }
    })
    .UseDefaultServiceProvider((context, options) =>
    {
        var isDevelopment = context.HostingEnvironment.IsDevelopment();
        options.ValidateScopes = isDevelopment;
        options.ValidateOnBuild = isDevelopment;
    });

    return builder;
}