B4J Question MQTT Subscribe Suback

Private Sub B4XPage_Created (Root1 As B4XView)
    Root = Root1
    Root.LoadLayout("MainPage")
    mqtt.Initialize("mqtt", "tcp://localhost:51044", "ttt")
    mqtt.Connect
    Wait For mqtt_Connected (Success As Boolean)
    If Success Then
        SubscribeWithActionListener("test", mqtt.QOS_2_EXACTLY_ONCE)
    End If
End Sub

Private Sub SubscribeWithActionListener(Topic As String, QOS As Int)
    Dim client As JavaObject = mqtt.As(JavaObject).GetField("client")
    Dim ActionListener As Object = client.CreateEventFromUI("org.eclipse.paho.client.mqttv3.IMqttActionListener", "ActionListener", Null)
    client.RunMethod("subscribe", Array(Topic, QOS, Null, ActionListener))
    Wait For ActionListener_Event (MethodName As String, Args() As Object)
    Log(MethodName & ": " & Args.As(List))
    If MethodName = "onSuccess" Then
        Dim token As JavaObject = Args(0)
        Dim grantedQos() As Int = token.RunMethod("getGrantedQos", Null)
        Log(grantedQos(0))
    End If
End Sub