当数据到达 Azure 队列时向连接的 IOT 设备发送消息？

Question

我有一个 Azure IOT Hub，一些 Arduino 设备 不时连接到它。我还有一个 Azure 队列，它可以包含 json 个字符串，当它们 已连接 时，我想将这些字符串发送到各个设备。

我按照 example for creating a webjob that gets called when data arrives in the queue. I also followed example 安排了一个作业，以便在 IOT 设备连接时向其发送数据。当运行单独时，两者都可以正常工作。

我结合了这些示例，因此当 ProcessQueueMessage() 因为队列中有内容而被调用时，我会安排一个作业将该数据发送到 IOT 设备。

public static async Task ProcessQueueMessage([QueueTrigger("inbox")] string message, ILogger logger)
{
  logger.LogInformation(message);
  Message = message;

  string methodJobId = Guid.NewGuid().ToString();
  await StartMethodJob(methodJobId, Message);
  MonitorJob(methodJobId).Wait();
}

但是，这样做导致了 SystemNullException，我不确定为什么。所有函数都是静态的，如果我单步执行它，我可以看到传入的参数有值。结果，它将队列项目移动到另一个队列 "inbox-poison"。

info: Function.ProcessQueueMessage.User[0]
      {"TransId":3517,"DeviceId":"Huzz_2_2_2","PriceAlert":{"Price":"High","Variance":0.0,"DisplaySetting":1,"Duration":60}}
fail: Function.ProcessQueueMessage[0]
      Executed 'Functions.ProcessQueueMessage' (Failed, Id=556812ab-4a58-4ae1-9f4f-6336962d92d2)
Microsoft.Azure.WebJobs.Host.FunctionInvocationException: Exception while executing function: Functions.ProcessQueueMessage ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at IncomeEligible.Alerts.Functions.StartMethodJob(String jobId, String json) in C:\source\repos\Income_Eligible_Price_Display\src\IncomeEligible.Alerts\IncomeEligible.Alerts\Functions.cs:line 46
   at IncomeEligible.Alerts.Functions.ProcessQueueMessage(String message, ILogger logger) in C:\source\repos\Income_Eligible_Price_Display\src\IncomeEligible.Alerts\IncomeEligible.Alerts\Functions.cs:line 80
   at Microsoft.Azure.WebJobs.Host.Executors.VoidTaskMethodInvoker`2.InvokeAsync(TReflected instance, Object[] arguments) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\VoidTaskMethodInvoker.cs:line 20
   at Microsoft.Azure.WebJobs.Host.Executors.FunctionInvoker`2.InvokeAsync(Object instance, Object[] arguments) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionInvoker.cs:line 52
   at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.InvokeAsync(IFunctionInvoker invoker, ParameterHelper parameterHelper, CancellationTokenSource timeoutTokenSource, CancellationTokenSource functionCancellationTokenSource, Boolean throwOnTimeout, TimeSpan timerInterval, IFunctionInstance instance) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 584
   at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ExecuteWithWatchersAsync(IFunctionInstanceEx instance, ParameterHelper parameterHelper, ILogger logger, CancellationTokenSource functionCancellationTokenSource) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 531
   at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ExecuteWithLoggingAsync(IFunctionInstanceEx instance, ParameterHelper parameterHelper, IFunctionOutputDefinition outputDefinition, ILogger logger, CancellationTokenSource functionCancellationTokenSource) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 467
   at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ExecuteWithLoggingAsync(IFunctionInstanceEx instance, FunctionStartedMessage message, FunctionInstanceLogEntry instanceLogEntry, ParameterHelper parameterHelper, ILogger logger, CancellationToken cancellationToken) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 277
   --- End of inner exception stack trace ---
   at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.ExecuteWithLoggingAsync(IFunctionInstanceEx instance, FunctionStartedMessage message, FunctionInstanceLogEntry instanceLogEntry, ParameterHelper parameterHelper, ILogger logger, CancellationToken cancellationToken) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 321
   at Microsoft.Azure.WebJobs.Host.Executors.FunctionExecutor.TryExecuteAsyncCore(IFunctionInstanceEx functionInstance, CancellationToken cancellationToken) in C:\projects\azure-webjobs-sdk-rqm4t\src\Microsoft.Azure.WebJobs.Host\Executors\FunctionExecutor.cs:line 117

以下是我的程序：

using Microsoft.Azure.Devices;
using Microsoft.Azure.Devices.Client;
using Microsoft.Azure.Devices.Shared;
using Microsoft.Azure.WebJobs;
using Microsoft.Extensions.Logging;
using System;
using System.Threading;
using System.Threading.Tasks;

namespace IncomeEligible.Alerts
{
  public class Functions
  {
    private static JobClient jobClient;
    private static int Count = 0;
    private static string Message = "";

    private static string deviceId = "Huzzah_w_DHT22";

    private const string DeviceConnectionString =
      "HostName=...";

    private const string HubConnectionString =
      "HostName=...";

    public static async Task MonitorJob(string jobId)
    {
      JobResponse result;
      do
      {
        result = await jobClient.GetJobAsync(jobId);
        Console.WriteLine("Job Status : " + result.Status.ToString());
        Thread.Sleep(2000);
      } while ((result.Status != JobStatus.Completed) &&
               (result.Status != JobStatus.Failed));
    }

    public static async Task StartMethodJob(string jobId, string json)
    {
      CloudToDeviceMethod directMethod =
        new CloudToDeviceMethod("SetPriceAlert", TimeSpan.FromSeconds(5), TimeSpan.FromSeconds(5));

      directMethod.SetPayloadJson(json);

      JobResponse result = await jobClient.ScheduleDeviceMethodAsync(jobId,
        $"DeviceId IN ['{deviceId}']",
        directMethod,
        DateTime.UtcNow,
        (long)TimeSpan.FromMinutes(2).TotalSeconds);

      Console.WriteLine("Started Method Job");
    }

    public static async Task ProcessQueueMessage([QueueTrigger("inbox")] string message, ILogger logger)
    {
      logger.LogInformation(message);
      Message = message;

      string methodJobId = Guid.NewGuid().ToString();
      await StartMethodJob(methodJobId, Message);
      MonitorJob(methodJobId).Wait();

    }

  }
}

如果工作正常，这种方法是否有意义，或者它是否更好，或者设置一个事件中心触发器或 IOT 中心触发器来检测设备何时连接并调用一个函数让它发送 json 到连接的设备？

感谢您的帮助！

Answer 1

jobClient 未分配任何值。

此外，您不希望将 async 与 .Wait() 和 Thread.Sleep() 等阻塞调用混合使用。请改用 await 和 await Task.Delay()。

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