0

I'm starting with IoT Hub and Azure services. I'm following this quickstart tutorial: Quickstart: Send telemetry from a device to an IoT hub and read it with a back-end application (.NET)

I created a Free Tier IoT Hub in my Azure account and registered a device using Azure Cloud Shell. Now I'm developing a "starter" library send D2C messages and I can see that it is possible to read sent messages. I have problems with the last step, it seems that the code is written in C# 8, but I'm developing with VS 2017 and get an error in a await foreach loop.

The sample code is here, and this is the code I want to change to C# 7:

private static async Task ReceiveMessagesFromDeviceAsync(CancellationToken cancellationToken)
{
    string connectionString = "{MyConnectionString}";
    await using EventHubConsumerClient consumer = new EventHubConsumerClient(EventHubConsumerClient.DefaultConsumerGroupName, connectionString, EventHubName);
    Console.WriteLine("Listening for messages on all partitions");

    try
    {
        await foreach (PartitionEvent partitionEvent in consumer.ReadEventsAsync(cancellationToken))
        {
            ...
        }
    }
    catch (TaskCanceledException)
    {
        ...
    }
}

This is the error I get in Visual Studio:

foreach statement cannot operate on variables of type 'IAsyncEnumerable' because 'IAsyncEnumerable' does not contain a public instance definition for 'GetEnumerator'

Is it possible to rewrite this line to use with C# 7?

Some details:

  • Visual Studio Professional 2017
  • Library target framework: .NET Core 2.1 .NET 4.7.2
Improve this question

1 Answer 1

Reset to default
1

It is possible to use the library without C# 8 by managing the enumerable manually. The basic form would look something like:

public static async Task Main(string[] args)
{
    var connection = "<< CONNECTION STRING >>" ;
    var hub = "<< EVENT HUB NAME >>";
    var producer = new EventHubProducerClient(connection, hub);
    var consumer = new EventHubConsumerClient(EventHubConsumerClient.DefaultConsumerGroupName, connection, hub);

    try
    {
        Console.WriteLine("Sending...");

        using (var batch = await producer.CreateBatchAsync())
        {
            for (var index = 0; index < 50; ++index)
            {
                batch.TryAdd(new EventData(Encoding.UTF8.GetBytes(index.ToString())));
            }

            await producer.SendAsync(batch);
        }

        Console.WriteLine("Reading...");

        var iterator = consumer.ReadEventsAsync(new ReadEventOptions { MaximumWaitTime = TimeSpan.FromMilliseconds(500) }).GetAsyncEnumerator();

        try
        {
            var consecutiveEmpties = 0;

            while (await iterator.MoveNextAsync())
            {
                var item = iterator.Current;

                if (item.Data != null)
                {
                    Console.WriteLine($"\tEvent: { Encoding.UTF8.GetString(item.Data.Body.ToArray()) }");
                    consecutiveEmpties = 0;
                }
                else if (++consecutiveEmpties > 5)
                {
                    break;
                }
            }
        }
        finally
        {
           await iterator.DisposeAsync();
        }

        Console.WriteLine("Done reading.");
    }
    finally
    {
        await producer.CloseAsync();
        await consumer.CloseAsync();
    }

    Console.ReadKey();
}

If you prefer, it is also possible to use C# 8 with Visual Studio 2017 by using the latest compilers package, as mentioned in the answer to this question.

Apologies; we've been intending a sample to demonstrate but have not yet had the opportunity to implement it. More context can be found in this GitHub issue.

Improve this answer
Sign up to request clarification or add additional context in comments.

1 Comment

Thank you! This works for me. I going to install the latest compiler to use C# new capabilities.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.