在验证服务描述符时，某些服务无法构建错误

Question

我有一个ASP.NET Core 5.0 MVC解决方案，

public abstract class HostedService : IHostedService, IDisposable
{
        private Task _currentTask;
        private readonly CancellationTokenSource _cancellationTokenSource = new 
        CancellationTokenSource();

        protected abstract Task ExecuteAsync(CancellationToken token);


        public virtual Task StartAsync(CancellationToken cancellationToken)
        {
            _currentTask = ExecuteAsync(cancellationToken);
            return _currentTask.IsCompleted ? _currentTask : Task.CompletedTask;
        }

        public virtual async Task StopAsync(CancellationToken cancellationToken)
        {
            if (_currentTask == null) return;
            try
            {
                _cancellationTokenSource.Cancel();
            }
            finally
            {
                await Task.WhenAny(_currentTask, Task.Delay(Timeout.Infinite, cancellationToken));
            }
        }

        public virtual void Dispose()
        {
            _cancellationTokenSource.Cancel();
        }
}

获取汇率

public class ExchangeSyncManager : HostedService
{
        private readonly CurrencyServices _currencyServices;
        private readonly ExchangeRateServices _exchangeRateServices;
        public ExchangeSyncManager(CurrencyServices currencyServices, ExchangeRateServices 
        exchangeRateServices)
        {
            _currencyServices = currencyServices;
            _exchangeRateServices = exchangeRateServices;
        }

        protected override async Task ExecuteAsync(CancellationToken token)
        {
            // işlem iptal edilmemişse…
            if (!token.IsCancellationRequested)
            {
                var url = "http://www.tcmb.gov.tr/kurlar/today.xml";
                XmlDocument xmlVerisi = new XmlDocument();
                List<ExchangeRate> list = new List<ExchangeRate>();
                xmlVerisi.Load(url);

                foreach (var currency in _currencyServices.GetCurrencies())
                {
                    var format = string.Format("Tarih_Date/Currency[@Kod='{0}']/ForexSelling", currency.Name);
                    var selectAndReplace = xmlVerisi.SelectSingleNode(format).InnerText.Replace('.', ',');
                    decimal value = Convert.ToDecimal(selectAndReplace);

                    list.Add(new ExchangeRate
                    {
                        Date = DateTime.Now,
                        Value = value,
                        CurrencyId = currency.Id
                    });
                }
                _exchangeRateServices.AddRange(list);

                await Task.Delay(TimeSpan.FromDays(1), token);
            }
        }
}

从URL和启动中

public void ConfigureServices(IServiceCollection services)
{
            services.AddControllersWithViews();
            
            //other services here
            ......................................................
            .....................................................
            services.AddScoped<CurrencyServices, CurrencyServices>();
            services.AddScoped<ExchangeRateServices>();
            services.AddHostedService<ExchangeSyncManager>();
}

：仍然会遇到此错误：

无法构建某些服务（在验证服务描述符的ServiceType时出现错误：Microsoft.extensions。 HOSTING.IHOSTEDSEVICE LIFETIME：SINGLETON IMPARINATIONTYTYPE：ipmms.business.managers.exchangesyncmanager'：无法从Singletleton'Microsoft.extensions.hosting.hosting.ihosterdserdserviceservice''''''''中，无法消费scoped服务'ipmms.business.services.currencyseress.currencyservices'

。

Answer 1

您不能在单身人士内注入示波器服务。它们受到HTTP请求的约束。
托管服务的一生是Singleton。
但是，您可以使用IserviceProvider创建范围并检索范围范围的服务实例。

您将在此处找到如何解决问题：
https://learn.microsoft.com/en-en-us/ dotnet/core/Extensions/Scoped-Service