在構建WebHost之前訪問宿主環境

Question

在我的Program.cs主要方法中，我想讀取user secrets，配置一個記錄器，然後構建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(); 
} 

我可以去配置通過建設自己的，但我很快就結束了亂七八糟試圖訪問託管環境屬性：

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(); 
} 

是否有訪問IHostingEnvironment一個更簡單的方法在構建WebHost之前？

Answer 1

在main方法中，在構建WebHost之前無法獲取IHostingEnvironment實例，因爲主機尚未創建。並且您無法正確創建新的有效實例，如it must be initialized using WebHostOptions`。

---

對於應用程序的名稱，你可以使用Assembly.GetEntryAssembly()?.GetName().Name

---

對於環境名稱使用你目前做（我認爲是這樣在你IsDevelopment使用（）方法）內容：

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

參見IHostingEnvironment.IsDevelopment()等方法爲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); 
    } 

---

注：關於AddJsonFile：作爲文件名是在Unix的OS敏感，有時是更好地使用$"appsettings.{envName.ToLower()}.json"代替。

Answer 2

我想做類似的事情。我想根據環境設置Kestrel聽選項。我只是在配置應用程序配置時將IHostingEnvironment保存爲本地變量。之後，我使用該變量根據環境做出決定。你應該能夠遵循這種模式來實現你的目標。

public class Program 
{ 
    public static void Main(string[] args) 
    { 
     BuildWebHost(args).Run(); 
    } 

    public static IWebHost BuildWebHost(string[] args) 
    { 
     IHostingEnvironment env = null; 

     return WebHost.CreateDefaultBuilder(args) 
       .UseStartup<Startup>() 
       .ConfigureAppConfiguration((hostingContext, config) => 
       { 
        env = hostingContext.HostingEnvironment; 

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

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

        config.AddEnvironmentVariables(); 

        if (args != null) 
        { 
         config.AddCommandLine(args); 
        } 
       }) 
       .UseKestrel(options => 
       { 
        if (env.IsDevelopment()) 
        { 
         options.Listen(IPAddress.Loopback, 44321, listenOptions => 
         { 
          listenOptions.UseHttps("testcert.pfx", "ordinary"); 
         }); 
        } 
        else 
        { 
         options.Listen(IPAddress.Loopback, 5000); 
        } 
       }) 
       .Build(); 
    } 
}