implemented functionality to subscribe on connect

ADIS_Csharp/RobotClientWpf/ChallengeFactory.cs

@@ -3,7 +3,7 @@ using RobotLib.Communication;
 
 namespace RobotClientWpf
 {
-    internal class ChallengeFactory
+    public class ChallengeFactory
     {
         public MqttPublisherSubscriber PublisherSubscriber { get; }
         public Robot RobotStationary { get; }
@@ -12,8 +12,8 @@ namespace RobotClientWpf
         public ChallengeFactory()
         {
             this.PublisherSubscriber = MqttPublisherSubscriber.Instance;
-            //this.RobotStationary = new Robot(this.PublisherSubscriber);
-            //this.RobotMobile = new Robot(this.PublisherSubscriber);
+            this.RobotStationary = new Robot(this.PublisherSubscriber);
+            this.RobotMobile = new Robot(this.PublisherSubscriber);
         }
     }
 }

ADIS_Csharp/RobotLib/Communication/MqttPublisherSubscriber.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.Text;
 using uPLibrary.Networking.M2Mqtt;
 using uPLibrary.Networking.M2Mqtt.Messages;
@@ -10,6 +11,7 @@ namespace RobotLib.Communication
         private MqttClient client;
         private static readonly NLog.Logger log = NLog.LogManager.GetCurrentClassLogger();
         private object clientLock = new object();
+        private List<string> toBeSubscribedTopics = new List<string>();
 
         /// <summary>
         /// Singleton pattern.
@@ -99,6 +101,15 @@ namespace RobotLib.Communication
                 
                 success = client.IsConnected;
                 log.Info($"Connecting done. Success = {success}");
+
+                // subscribe to topics that have already been appended
+                if(success)
+                {
+                    foreach (var topic in toBeSubscribedTopics)
+                    {
+                        this.OnlineSubscribe(topic);
+                    }
+                }
             }
             return success;
         }
@@ -141,6 +152,11 @@ namespace RobotLib.Communication
 
         public void Publish(string topic, string message)
         {
+            if(this.IsConnected == false)
+            {
+                log.Warn($"Message was discarded, Mqtt broker not connected. Destination topic={topic}");
+                return;
+            }
             lock (clientLock)
             {
                 var msgId = client.Publish(topic, Encoding.ASCII.GetBytes(message));
@@ -149,6 +165,20 @@ namespace RobotLib.Communication
         }
 
         public void Subscribe(string topic)
+        {
+            // add to list if not already there
+            if(toBeSubscribedTopics.Contains(topic) == false)
+            {
+                toBeSubscribedTopics.Add(topic);
+                log.Debug($"Added topic '{topic}'. To the to be subscribed list.");
+            }
+            if (this.IsConnected)
+            {
+                OnlineSubscribe(topic);
+            }
+        }
+
+        private void OnlineSubscribe(string topic)
         {
             lock (clientLock)
             {