asp.net-core - 在构建 WebHost 之前访问托管环境

Question

在我的 Program.cs Main 方法中，我想读取 user secrets ，配置记录器，然后构建 WebHost。

public static Main(string[] args)
{

    string instrumentationKey = null; // read from UserSecrets

    Log.Logger = new LoggerConfiguration()
        .MinimumLevel.Debug()
        .WriteTo.ApplicationInsightsEvents(instrumentationKey)
        .CreateLogger();

    BuildWebHost(args).Run();
} 

我可以通过构建自己的配置来获取配置，但我很快就会在尝试访问托管环境属性时陷入困惑:

public static Main(string[] args)
{
    var envName = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ?? "Production";
    var configBuilder = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
        .AddJsonFile($"appsettings.{envName}.json", optional: true, reloadOnChange: true);

    // Add user secrets if env.IsDevelopment().
    // Normally this convenience IsDevelopment method would be available 
    // from HostingEnvironmentExtensions I'm using a private method here.
    if (IsDevelopment(envName))
    {
        string assemblyName = "<I would like the hosting environment here too>"; // e.g env.ApplicationName
        var appAssembly = Assembly.Load(new AssemblyName(assemblyName));
        if (appAssembly != null)
        {
            configBuilder.AddUserSecrets(appAssembly, optional: true); // finally, user secrets \o/
        }
    }
    var config = configBuilder.Build();
    string instrumentationKey = config["MySecretFromUserSecretsIfDevEnv"];

    Log.Logger = new LoggerConfiguration()
        .MinimumLevel.Debug()
        .WriteTo.ApplicationInsightsEvents(instrumentationKey) // that.. escallated quickly
        .CreateLogger();

    // webHostBuilder.UseConfiguration(config) later on..
    BuildWebHost(args, config).Run();
}

在构建 WebHost 之前，是否有更简单的方法来访问 IHostingEnvironment？

Answer 1

在 main 方法中，您无法在构建 WebHost 之前获取 IHostingEnvironment 实例，因为尚未创建托管。而且您无法正确创建新的有效实例，如 it must be initialized using WebHostOptions` .

---

对于应用程序名称，您可以使用 Assembly.GetEntryAssembly()?.GetName().Name

---

对于环境名称，请使用您当前所做的(我假设您的 IsDevelopment() 方法中使用了类似这样的内容):

var environmentName = System.Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");
bool isDevelopment = string.Equals(
           "Development",
            environmentName,
            StringComparison.OrdinalIgnoreCase);

看，像 IHostingEnvironment.IsDevelopment() 这样的方法是 extension methods that simply do string comparison internally :

    public static bool IsDevelopment(this IHostingEnvironment hostingEnvironment)
    {
        if (hostingEnvironment == null)
        {
            throw new ArgumentNullException(nameof(hostingEnvironment));
        }

        return hostingEnvironment.IsEnvironment(EnvironmentName.Development);
    }


    public static bool IsEnvironment(
        this IHostingEnvironment hostingEnvironment,
        string environmentName)
    {
        if (hostingEnvironment == null)
        {
            throw new ArgumentNullException(nameof(hostingEnvironment));
        }

        return string.Equals(
            hostingEnvironment.EnvironmentName,
            environmentName,
            StringComparison.OrdinalIgnoreCase);
    }

---

关于 AddJsonFile 的注意事项:由于文件名在 Unix 操作系统中很敏感，有时最好使用 $"appsettings.{envName.ToLower()}.json"的。