Im having trouble converting wpf to asp.net using mqtt. My code did not show any error but when i launch and input some text and a button click,it will show me an error "An exception of type 'System.NullReferenceException' occurred in WebApplication4.dll but was not handled in user code"
public partial class Testing : System.Web.UI.Page
{
MqttClient client;
string clientId;
protected void Page_Load(object sender, EventArgs e)
{
}
public void MainWindow()
{
string BrokerAddress = "test.mosquitto.org";
client = new MqttClient(BrokerAddress);
// register a callback-function (we have to implement, see below) which is called by the library when a message was received
client.MqttMsgPublishReceived += client_MqttMsgPublishReceived;
// use a unique id as client id, each time we start the application
clientId = Guid.NewGuid().ToString();
client.Connect(clientId);
}
void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e)
{
string ReceivedMessage = Encoding.UTF8.GetString(e.Message);
txtReceived.Text = ReceivedMessage;
}
protected void btnPublish_Click(object sender, EventArgs e)
{
if (txtTopicPublish.Text != "")
{
// whole topic
string Topic = "" + txtTopicPublish.Text + "";
// publish a message with QoS 2
client.Publish(Topic, Encoding.UTF8.GetBytes(txtPublish.Text), MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE, true);
}
else
{
Page.ClientScript.RegisterStartupScript(this.GetType(), "Scripts", "<script>alert('You have to enter a topic to publish!')</script>");
}
}