Android Tutorial [B4X] MQTT - Connect & Reconnect

The ConnectAndReconnect sub takes care of connecting to the broker and reconnecting if the connection has broken.
It sends a "ping" request every 5 seconds to help the MQTT client recognize network failures.

It is a nice example of how Wait For and Sleep can help to manage the network state which is completely asynchronous.
The ConnectAndReconnect sub will keep running until you set the working variable to False.

Code:

Sub ConnectAndReconnect
   Do While working
     If mqtt.IsInitialized Then mqtt.Close
     mqtt.Initialize("mqtt", "ssl://io.adafruit.com:8883", "B4X" & Rnd(0, 999999999))
     Dim mo As MqttConnectOptions
     mo.Initialize(username, password)
     Log("Trying to connect")
     mqtt.Connect2(mo)
     Wait For Mqtt_Connected (Success As Boolean)
     If Success Then
       Log("Mqtt connected")
       Do While working And mqtt.Connected
         mqtt.Publish2("ping", Array As Byte(0), 1, False) 'change the ping topic as needed
         Sleep(5000)
       Loop
       Log("Disconnected")
     Else
       Log("Error connecting.")
     End If
     Sleep(5000)
   Loop
End Sub

In B4A it is recommended to put it in the starter service:

Code:

Sub Process_Globals
   Private working As Boolean = True
   Private mqtt As MqttClient
End Sub

Sub Service_Create
   working = True
   ConnectAndReconnect
End Sub

Set working to False before you close the connection when you want to close it.

This code is compatible with B4A, B4i and B4J.