Question

我试图在其中使用HostBuilder的.net核心控制台应用程序中包含一个appsettings.json文件，并尝试向配置中添加一个部分（AppVars）。当我尝试执行此操作时，出现错误：

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"));

            });

       ...
    }

在下面，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"));

在构造函数只期望IOptions<AppVars>时注册AppVars

请相应地更新目标构造函数，以便期望正确的类型

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

按原样保留构造函数，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);

        });

将应用程序设置配置DI添加到HostBuilder控制台应用程序

1 个答案: