c# - 如何在更改 dotnet core 3 控制台应用程序时重新加载 'appsettings.json'

Question

我正在尝试设置一个控制台应用程序来重新加载“appsettings.json”，但我无法让它对文件的更改使用react。

我已经像这样设置了主要的:

private static void Main ()
    {
        configuration = LoadConfiguration ();

        var services = ConfigureServices ();

        var serviceProvider = services.BuildServiceProvider ();

        serviceProvider.GetService<ConsoleApp> ().Run ();
    }

    private static IConfiguration LoadConfiguration ()
        => new ConfigurationBuilder ().SetBasePath (GetApplicationDirectory ())
                                      .AddJsonFile (_APP_SETTING_FILE_NAME, optional: false, reloadOnChange: true)
                                      .Build ();

    private static IServiceCollection ConfigureServices ()
    {
        IServiceCollection services = new ServiceCollection ();

        configuration.Bind (new AppSettings ()); // binds the 'appsettings.json' to the class

        services.AddSingleton (configuration);
        services.AddTransient<ConsoleApp> ();

        services.AddOptions<AppSettings> ();  // adds the IOption<T> and IOptionMonitor<T>

        // here I'm trying to follow a post from Dino Esposito [https://www.red-gate.com/simple-talk/dotnet/net-development/asp-net-core-3-0-configuration-factsheet/][1] but services.Configure<AppSettings>() does not compile
        // the failure could be here? :-(
        services.Configure<AppSettings> (opt => opt.Default = configuration["Default"]);

        return services;
    }

我很确定我在 DI 的配置中做错了什么，但我不知道是什么。

控制台应用程序非常简单，应该注册 cahgne 但没有注册，反正就在这里

public class ConsoleApp
{
    public AppSettings AppSettings { get; }

    public ConsoleApp (IOptionsMonitor<AppSettings> appSettingsOptionsMonitor)
    {
        AppSettings = appSettingsOptionsMonitor.CurrentValue;

        appSettingsOptionsMonitor.OnChange ((arg1, arg2) => Console.WriteLine ($"\t ---> AppSettings changed to '{arg1.Default}' - '{arg2}'"));

        Console.WriteLine ($"ctor - appsettings current value: '{AppSettings.Default}'.\n");
    }

    public void Run ()
    {
        Console.WriteLine ($"\tCurrent value: '{AppSettings.Default}' - waiting for change ...");

        while (AppSettings.Default != "Stop") { }

        Console.WriteLine ($"\t... has changed to '{AppSettings.Default}'.");
    }
}

AppSettings 类是:

public class AppSettings
{
    public string Default { get; set; }
}

如有任何帮助，我们将不胜感激!

T'X彼得

Answer 1

不能使用扩展方法AddOptions去做这个，因为它不是为与文件配置提供程序一起工作而设计的。为此，您必须使用 OptionsConfigurationServiceCollectionExtensions 类中的扩展方法。

关键在OptionsConfigurationServiceCollectionExtensions类和 OptionsMonitor类(class)。您可以在 OptionsMonitor 类的构造函数中看到，它会获取服务容器中注册的所有 IOptionsChangeTokenSource 实例，这些实例是通过 OptionsConfigurationServiceCollectionExtensions.Configure 方法注册的。IOptionsChangeTokenSource 实例会在配置文件更改时重新加载选项。

作为比较，您可以在 AddOptions 中看到方法，它不会注册 IOptionsChangeTokenSource 实例。