XMPP functionality in the App Delegate for Instant chat service in xocde(iOS)

inserting the XMPP functionality in the App Delegate is a great way to make the functionality easily available throughout the app.

1	[[UIApplication sharedApplication] delegate]

The XMPP class will dispatch events by means of protocols which we will define below. This is the list of events handled by this class:

·       The client connected with the server

·       The client authenticated with the server

·       The client received a notification of presence (e.g. a user logged in)

·       The client received a message

XMPPStream will be the barebone of our client-server communication system and all messages will be exchanged through it. We will also define the methods to manage connection and disconnection. 

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@interface JabberClientAppDelegate() - (void)setupStream; - (void)goOnline; - (void)goOffline; @end @implementation JabberClientAppDelegate @end

Here, the most important is setupStream, which creates the channel to manage the exchange of messages.

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- (void)setupStream {     xmppStream = [[XMPPStream alloc] init];     [xmppStream addDelegate:self delegateQueue:dispatch_get_main_queue()]; }

Just two lines of code, but behind that many things happen. The dispatch_get_main_queue() is a function which returns a reference
to the system level asynchronous execution mechanism, to which we can sumbit tasks and receive notifications. 

Offline and Online functions are able to notify other users when we are connected or not. They are defined by sending an XMPPPresence object through the socket. The server will dispatch the notification accordingly.

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- (void)goOnline {     XMPPPresence *presence = [XMPPPresence presence];     [[self xmppStream] sendElement:presence]; } - (void)goOffline {     XMPPPresence *presence = [XMPPPresence presenceWithType:@"unavailable"];     [[self xmppStream] sendElement:presence]; }

The connect method is the most important, for it manages the login operation. It returns a boolean representing whether the connection was successful or not. At first it sets up the stream, then it uses data stored in NSUserDefaults to decorate the stream and call a connect message. An alert view is displayed if the connection is not successful.

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- (BOOL)connect {     [self setupStream];     NSString *jabberID = [[NSUserDefaults standardUserDefaults] stringForKey:@"userID"];     NSString *myPassword = [[NSUserDefaults standardUserDefaults] stringForKey:@"userPassword"];     if (![xmppStream isDisconnected]) {         return YES;     }     if (jabberID == nil || myPassword == nil) {         return NO;     }     [xmppStream setMyJID:[XMPPJID jidWithString:jabberID]];     password = myPassword;     NSError *error = nil;     if (![xmppStream connect:&error])     {         UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Error"                                                             message:[NSString stringWithFormat:@"Can't connect to server %@", [error localizedDescription]]                                                            delegate:nil                                                   cancelButtonTitle:@"Ok"                                                   otherButtonTitles:nil];         [alertView show];         [alertView release];         return NO;     }     return YES; }

For sake of completeness, we also implement the disconnect method which is defined as follows:

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- (void)disconnect {     [self goOffline];     [xmppStream disconnect]; }

Now that we have some of the basic functions we can use them in specific cases, for example, when the application becomes active or inactive.

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- (void)applicationWillResignActive:(UIApplication *)application {     [self disconnect]; } - (void)applicationDidBecomeActive:(UIApplication *)application {     [self connect]; }

We are left with the core of the system, the notifications of events and related behaviors, which we implement by means of protocols.