c# - 将 appsettings 配置 DI 添加到 HostBuilder 控制台应用程序

Question

我正在尝试在使用 HostBuilder 的 .net 核心控制台应用程序中包含一个 appsettings.json 文件，并尝试将一个部分（AppVars）添加到配置中。当我尝试这样做时，我收到错误：

System.InvalidOperationException: Unable to resolve service for type AppVars while attempting to activate...

这是我的代码：

private static async Task Main(string[] args)
    {
        var isService = !(Debugger.IsAttached || args.Contains("--console"));



        var config1 = new ConfigurationBuilder()
            .SetBasePath(Directory.GetCurrentDirectory())
            .AddJsonFile("appsettings.json", optional: true)
            .Build();

        var builder = new HostBuilder()
            .ConfigureServices((hostContext, services) =>
            {
                services.AddHostedService<FileWriterService>();

                services.Configure<AppVars>(config1.GetSection("AppVars"));

            });

       ...
    }

下面我试图在一个类中注入 AppVars：

public class FileWriterService : IHostedService, IDisposable
{
    private const string Path = @"d:\TestApplication.txt";

    private Timer _timer;
    private AppVars _appVars;
    public FileWriterService(AppVars appVars)
    {
       //_appVars = appVars;
    }

Answer 1

 services.Configure<AppVars>(config1.GetSection("AppVars"));

IOptions<AppVars>在构造函数期望时注册AppVars

相应地更新目标构造函数，以便它期望正确的类型

public class FileWriterService : IHostedService, IDisposable {
    private const string Path = @"d:\TestApplication.txt";

    private Timer _timer;
    private AppVars _appVars;
    public FileWriterService(IOptions<AppVars> appVars) {
       _appVars = appVars.Value;
    }

    //...

}

或者

保持构造函数不变，并重构启动以注册所需的类型

   var config1 = new ConfigurationBuilder()
        .SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("appsettings.json", optional: true)
        .Build();

    var builder = new HostBuilder()
        .ConfigureServices((hostContext, services) => {
            services.AddHostedService<FileWriterService>();
            AppVars appVars = config1.GetSection("AppVars").Get<AppVars>();
            services.AddSingleton(appVars);

        });