Following this example I have now therefore been required to update the MQTT.NET from version 3 (that works thanks the provided help) to version 4.

A very basic set of capabilities would be enough:

1. Connect to an adress with a timeout
2. Check if the connection has gone well
3. Receive messages
4. check disconnection

that was extremely easy in version 3

MqttClientOptionsBuilder builder = new MqttClientOptionsBuilder()
                                .WithClientId("IoApp"   HelperN.MQTT.GetClientID(true))
                                .WithTcpServer("localhost", 1883);

ManagedMqttClientOptions options = new ManagedMqttClientOptionsBuilder()
                                .WithAutoReconnectDelay(TimeSpan.FromSeconds(60))
                                .WithClientOptions(builder.Build())
                                .Build();

mqttClient = new MqttFactory().CreateManagedMqttClient();

mqttClient.ConnectedHandler = new MqttClientConnectedHandlerDelegate(OnConnected);
mqttClient.DisconnectedHandler = new MqttClientDisconnectedHandlerDelegate(OnDisconnected);
mqttClient.ConnectingFailedHandler = new ConnectingFailedHandlerDelegate(OnConnectingFailed);

mqttClient.SubscribeAsync(...);
mqttClient.SubscribeAsync(...);
mqttClient.StartAsync(options).GetAwaiter().GetResult();

mqttClient.UseApplicationMessageReceivedHandler(args => { OnMessageReceived(args); });

but when it comes to version 4 if I have to relay on those examples I have problems. Let's start from the connection

public static async Task Connect_Client_Timeout()
{
    /*
     * This sample creates a simple MQTT client and connects to an invalid broker using a timeout.
     * 
     * This is a modified version of the sample _Connect_Client_! See other sample for more details.
     */

    var mqttFactory = new MqttFactory();
    strError = String.Empty;

    using (var mqttClient = mqttFactory.CreateMqttClient())
    {
        var mqttClientOptions = new MqttClientOptionsBuilder().WithTcpServer("aaaa127.0.0.1",1883).Build();

        try
        {
                
            using (var timeoutToken = new CancellationTokenSource(TimeSpan.FromSeconds(5)))
            {
                await mqttClient.ConnectAsync(mqttClientOptions, timeoutToken.Token);
            }
        }
        catch (OperationCanceledException exc)
        {
            strError = "Connect_Client_Timeout exc:"   exc.Message;
        }
    }
}

And I call this task from the main awaiting the result.

var connectTask  = Connect_Client_Timeout();
connectTask.Wait();<-----never ends

Since I put a wrong address "aaaa127.0.0.1" I expect a failure after 5 seconds. But the connectTask.Wait never end. But even if I put the right address "127.0.0.1" it never exits. So perhaps the error stands in the connectTask.Wait();.

Thanks

CodePudding user response：

The solution is here In short you have to do this:

static async Task  Connect()
{
    IManagedMqttClient _mqttClient = new MqttFactory().CreateManagedMqttClient();

    // Create client options object
    MqttClientOptionsBuilder builder = new MqttClientOptionsBuilder()
                                        .WithClientId("behroozbc")
                                        .WithTcpServer("localhost");
    ManagedMqttClientOptions options = new ManagedMqttClientOptionsBuilder()
                                .WithAutoReconnectDelay(TimeSpan.FromSeconds(60))
                                .WithClientOptions(builder.Build())
                                .Build();



    // Set up handlers
    _mqttClient.ConnectedAsync  = _mqttClient_ConnectedAsync;


    _mqttClient.DisconnectedAsync  = _mqttClient_DisconnectedAsync;


    _mqttClient.ConnectingFailedAsync  = _mqttClient_ConnectingFailedAsync;


    // Connect to the broker
    await _mqttClient.StartAsync(options);

    // Send a new message to the broker every second
    while (true)
    {
        string json = JsonSerializer.Serialize(new { message = "Hi Mqtt", sent = DateTime.UtcNow });
        await _mqttClient.EnqueueAsync("behroozbc.ir/topic/json", json);

        await Task.Delay(TimeSpan.FromSeconds(1));
    }
    Task _mqttClient_ConnectedAsync(MqttClientConnectedEventArgs arg)
    {
        Console.WriteLine("Connected");
        return Task.CompletedTask;
    };
    Task _mqttClient_DisconnectedAsync(MqttClientDisconnectedEventArgs arg)
    {
        Console.WriteLine("Disconnected");
        return Task.CompletedTask;
    };
    Task _mqttClient_ConnectingFailedAsync(ConnectingFailedEventArgs arg)
    {
        Console.WriteLine("Connection failed check network or broker!");
        return Task.CompletedTask;
    }
}

and then just call Connect() and rely on the subscribed examples