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Author: jmesnil

MQTTExample/MQTTViewController.m

@@ -14,8 +14,10 @@
 
 @interface MQTTViewController ()
 
+// this UISwitch will be used to display the status received from the topic.
 @property (weak, nonatomic) IBOutlet UISwitch *subscribedSwitch;
 
+// create a property for the MQTTClient that is used to send and receive the message
 @property (nonatomic, strong) MQTTClient *client;
 
 @end
@@ -26,54 +28,62 @@ - (void)viewDidLoad
 {
     [super viewDidLoad];
 
+    // create the MQTT client with an unique identifier
     NSString *clientID = [UIDevice currentDevice].identifierForVendor.UUIDString;
     self.client = [[MQTTClient alloc] initWithClientId:clientID];
 
+    // keep a reference on the switch to avoid having a reference to self in the
+    // block below (retain/release cycle, blah blah blah)
     UISwitch *subSwitch = self.subscribedSwitch;
 
-    // define the message handler that will handle the received MQTT messages
+    // define the handler that will be called when MQTT messages are receive by the client
     [self.client setMessageHandler:^(MQTTMessage *message) {
+        // extract the switch status from the message payload
         BOOL on = [message.payloadString boolValue];
+
         // the MQTTClientDelegate methods are called from a GCD queue.
         // Any update to the UI must be done on the main queue
         dispatch_async(dispatch_get_main_queue(), ^{
             [subSwitch setOn:on animated:YES];
         });
     }];
+
     // connect the MQTT client
     [self.client connectToHost:kMQTTServerHost completionHandler:^(NSUInteger code) {
+        // The client is connected when this completion handler is called
         NSLog(@"client is connected with id %@", clientID);
-        // once the client is connected, subscribe to the topic
-        [self.client subscribe:kTopic
-         withCompletionHandler:^(NSArray *grantedQos) {
+        // Subscribe to the topic
+        [self.client subscribe:kTopic withCompletionHandler:^(NSArray *grantedQos) {
+            // The client is effectively subscribed to the topic when this completion handler is called
              NSLog(@"subscribed to topic %@", kTopic);
          }];
     }];
 }
 
 - (void)dealloc
 {
+    // disconnect the MQTT client
     [self.client disconnectWithCompletionHandler:^(NSUInteger code) {
+        // The client is disconnected when this completion handler is called
         NSLog(@"MQTT is disconnected");
     }];
 }
-- (void)didReceiveMemoryWarning
-{
-    [super didReceiveMemoryWarning];
-    // Dispose of any resources that can be recreated.
-}
 
 #pragma mark - IBActions
 
+// This method is called when the "published LED" switch status changes
 - (IBAction)switchUpdated:(id)sender {
     BOOL on = [sender isOn];
     NSString *payload = [NSNumber numberWithBool:on].stringValue;
 
+    // use the MQTT client to send a message with the switch status to the topic
     [self.client publishString:payload
                        toTopic:kTopic
                        withQos:AtMostOnce
                         retain:YES
              completionHandler:nil];
+    // we passed nil to the completionHandler as we are not interested to know
+    // when the message was effectively sent
 }
 
 @end