使用 Hangfire 创建重复作业时出错答案

【问题标题】：Error while creating recurring job using Hangfire使用 Hangfire 创建重复作业时出错
【发布时间】：2017-10-12 08:28:48
【问题描述】：

我正在尝试在我的应用程序中使用 Hangfire 来获取（从外部 API）每天的货币兑换率并插入应用程序数据库。成功配置（这样想）并且在数据库中创建了 Hangfire 表，并且 Job 表有条目但 Job 没有成功执行，并且在检查 State Table 时它显示失败并有类似

的错误消息

{"FailedAt":"2017-10-12T07:55:00.3075439Z",
  "ExceptionType":"System.MissingMethodException",
  "ExceptionMessage":"Cannot create an instance of an interface.",
  "ExceptionDetails":"System.MissingMethodException: Cannot create an instance of an interface.\r\n  
   at System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck)\r\n  
    at System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)\r\n  
     at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark)\r\n 
       at System.Activator.CreateInstance(Type type, Boolean nonPublic)\r\n   at System.Activator.CreateInstance(Type type)\r\n   at Hangfire.JobActivator.ActivateJob(Type jobType)\r\n   
       at Hangfire.JobActivator.SimpleJobActivatorScope.Resolve(Type type)\r\n   at Hangfire.Server.CoreBackgroundJobPerformer.Perform(PerformContext context)\r\n   
       at Hangfire.Server.BackgroundJobPerformer.<>c__DisplayClass8_0.<PerformJobWithFilters>b__0()\r\n   
       at Hangfire.Server.BackgroundJobPerformer.InvokePerformFilter(IServerFilter filter, PerformingContext preContext, Func`1 continuation)\r\n   
       at Hangfire.Server.BackgroundJobPerformer.<>c__DisplayClass8_1.<PerformJobWithFilters>b__2()\r\n   
       at Hangfire.Server.BackgroundJobPerformer.PerformJobWithFilters(PerformContext context, IEnumerable`1 filters)\r\n   
       at Hangfire.Server.BackgroundJobPerformer.Perform(PerformContext context)\r\n   
       at Hangfire.Server.Worker.PerformJob(BackgroundProcessContext context, IStorageConnection connection, String jobId)"}

使用的代码：

    public partial class Startup
        {
            public void Configuration(IAppBuilder app)
            {
                ConfigureAuth(app);
 GlobalConfiguration.Configuration.UseSqlServerStorage("ERPContext");

                RecurringJob.AddOrUpdate<IAPIRequest>(x => x.ProcessCurrencyConversion(), Cron.MinuteInterval(1));
                app.UseHangfireDashboard();
                app.UseHangfireServer();

            }
        }

具有要执行的方法的接口和类

 public interface IAPIRequest
    {
        void ProcessCurrencyConversion();
    }

 public class APIRequest : IAPIRequest
    {
        public void ProcessCurrencyConversion()
        {
           WebClient client = new WebClient();

            string urlPattern = "https://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20yahoo.finance.xchange%20where%20pair%20in%20(%22USDKWD,EURKWD,GBPKWD,AEDKWD,ZARKWD%22)&format=json&env=store%3A%2F%2Fdatatables.org%2Falltableswithkeys";

            var jsonResult = client.DownloadString(urlPattern);
            dynamic results = JsonConvert.DeserializeObject<dynamic>(jsonResult);
            var rates = results.rate;
            List<CurrencyJSON> currencies = new List<CurrencyJSON>();
            using (var db = new ERPContext())
            {

                foreach (var rate in rates)
                {
                    var currencyJson = new CurrencyJSON();//POCO
                    currencyJson.Bid = rate.Bid;
                    currencyJson.Name = rate.Name;

                    currencies.Add(currencyJson);
                }

                db.Configuration.AutoDetectChangesEnabled = false;
                db.Configuration.ValidateOnSaveEnabled = false;

                db.CurrencyJson.ToList().AddRange(currencies);
                db.SaveChanges();
            }
        }
    }

我做错了什么？感谢任何帮助，在此先感谢。已经检查过here 发布的类似问题，但没有帮助。

【问题讨论】：

Hangfire 似乎默认不支持接口，而是需要 IoC 库将接口映射到类型。见discuss.hangfire.io/t/architecture-questions/1167/2 和discuss.hangfire.io/t/cannot-create-an-instance-of-an-interface/…。

标签： c# asp.net-mvc hangfire

【解决方案1】：

正如@Diado 在 cmets 中指出的那样，如果使用接口，HangFire 需要 IoC，因为没有默认支持。或者你可以直接使用类而不是接口。

https://github.com/devmondo/HangFire.SimpleInjector 是我使用的 IoC 注入器之一。

【讨论】：