Usage Examples

The following serves as a few examples on how to utilize the built in event system.

Pattern

All events are available on the client instance: client.<event_name>.

Handlers can be assigned to the event by simply adding your handler to the list. Handlers can be either a pre-defined function or a lambda (illustrated in the next section).

client.AfterDisconnect += MyAfterDisconnectHandler;

...where MyAfterDisconnectHandler is an already-defined function in my application with the following signature:

static void MyAfterDisconnectHandler(object? sender, AfterDisconnectEventArgs eventArgs)

Lambdas

An alternative to using a pre-defined function are lambdas:

client.AfterUnsubscribe += (sender, args) =>
{
    // code
};

Event Arguments

The definitions for all event arguments can be found here.

Display Options Prior to Connecting

This example simply prints out the HiveMQClientOptions prior to the connect command being sent to the broker.

using HiveMQtt.Client.Events;

private static void BeforeConnectHandler(object? sender, BeforeConnectEventArgs eventArgs)
{
    if (sender is not null)
    {
        var client = (HiveMQClient)sender;
        Console.WriteLine($"Connecting to Broker with the Options: {eventArgs.Options}");
    }
}

// Later...

var client = new HiveMQClient();

client.BeforeConnect += BeforeConnectHandler;
var connectResult = await client.ConnectAsync().ConfigureAwait(false);

Taking Action After a Subscribe

Suppose you wanted to take some global action after every subscribe call made by the client. This example illustrates the steps required.

using HiveMQtt.Client.Events;

private static void AfterSubscribeHandler(object? sender, AfterSubscribeEventArgs eventArgs)
{
    if (sender is not null)
    {
        var client = (HiveMQClient)sender;

        // The result of the subscribe call
        // eventArgs.SubscribeResult
    }
}

// Later...

var client = new HiveMQClient();

client.AfterSubscribe += AfterSubscribeHandler;
var connectResult = await client.ConnectAsync().ConfigureAwait(false);
var subscribeResult = await client.SubscribeAsync("district/9/level", MQTT5.Types.QualityOfService.ExactlyOnceDelivery).ConfigureAwait(false);

Monitoring outgoing Publish Packets

The following can be used to monitor when publish packets are transmitted from the client. A potential debug vector in application development.

using HiveMQtt.Client.Events;

private static void OnPublishSentHandler(object? sender, OnPublishSentEventArgs eventArgs)
{
    if (sender is not null)
    {
        var client = (HiveMQClient)sender;

        // The transmitted MQTT Publish packet
        // eventArgs.PublishPacket

        // and the MQTT5PublishMessage
        // eventArgs.PublishPacket.Message

    }
}

// Later...

var client = new HiveMQClient();
var connectResult = await client.ConnectAsync().ConfigureAwait(false);

client.OnPublishSent += OnPublishSentHandler;

var result = await client.PublishAsync("district/7/count", "82", MQTT5.Types.QualityOfService.AtLeastOnceDelivery).ConfigureAwait(false);

Monitoring Subscribe Response Packets (SUBACK)

The following can be used to monitor SubAck responses from the broker

using HiveMQtt.Client.Events;

private static void OnSubAckReceivedHandler(object? sender, OnSubAckReceivedEventArgs eventArgs)
{
    if (sender is not null)
    {
        var client = (HiveMQClient)sender;

        // The received SubAck packet
        // eventArgs.SubAckPacket
    }
}

// Later...

var client = new HiveMQClient();
client.OnSubAckReceived += OnSubAckReceivedHandler;
var connectResult = await client.ConnectAsync().ConfigureAwait(false);
var subResult = await client.SubscribeAsync("district/9/level", MQTT5.Types.QualityOfService.ExactlyOnceDelivery).ConfigureAwait(false);