Windows Azure Mobile Services Part 2

Episode Links

Episode Source Code

Presenting the Chat View Controller

The MessagesTableViewController docs mention that it doesn't play nicely with storyboards, so we simply create & present it with code:

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    if ([self promptIfNoUserOrContinue]) {
        NSCChatViewController *chatVC = [[NSCChatViewControlleralloc] init];
        chatVC.client = self.client;
        chatVC.room = self.rooms[indexPath.row];
        [self.navigationControllerpushViewController:chatVC animated:YES];
    }
}

Note that we have to set the client and the room that we want to use for the chat view controller.

Maintaining the User's current Room

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    [self setUserRoomId:@(self.room.roomId)];
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    [self stopPolling];
    [self setUserRoomId:[NSNull null]];
}

This isn't a bullet proof solution, but will work fine enough for our needs.

- (void)setUserRoomId:(id)roomId {
    MSTable *users = [self.clientgetTable:@"Users"];
    id values = @{@"roomId": roomId, @"id": [[NSUserDefaultsstandardUserDefaults] objectForKey:@"userId"]};
    [users update:values
       completion:^(NSDictionary *item, NSError *error) {
           if (error) {
               NSLog(@"ERROR: %@", error);
           } else {
               NSLog(@"User room updated to %@", roomId);
           }
       }];
}

Note here that we're trusting the client to post a valid room id. In general you shouldn't trust your clients at all, so we'd have to add some defensive programming on the server to validate that this is a valid id.

Fetching the messages for the room

We're dynamically fetching the messages for the room by date, so we have to handle both cases: initial fetch where we want no animation, and incremental fetches that should animate in the rows and scroll to the bottom.

- (void)fetchMessages {
    [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
    NSLog(@"Checking for messages since %@", self.lastFetchDate);
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"roomId = %d and createdAt > %@", self.room.roomId, self.lastFetchDate];
    MSQuery *query = [[self messagesTable] queryWhere:predicate];
    [query readWithCompletion:^(NSArray *items, NSInteger totalCount, NSError *error) {
        self.lastFetchDate = [NSDate date];
        if (items) {
            NSLog(@"Found messages: %@", items);
            if (!self.messages) {
                self.messages = [NSMutableArray array];
                [self.messages addObjectsFromArray:[self messageArrayForDictionaries:items]];
                [self.tableView reloadData];
                [self scrollToBottomAnimated:NO];
            } else {
                NSMutableArray *messagesToAdd = [NSMutableArray array];
                for (id msgDictionary in items) {
                    NSCMessage *message = [NSCMessage messageWithDictionary:msgDictionary];
                    if (![self.messages containsObject:message]) {
                        [messagesToAdd addObject:message];
                    }
                }

                if ([messagesToAdd count] > 0) {
                    [selfinsertMessages:messagesToAdd];
                }
            }

            [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
        } else {
            NSLog(@"ERROR: %@", error);
            [[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
        }
    }];
}

This method used some supplementary methods:

  - (void)insertMessages:(NSArray *)messages {
    [self.tableView beginUpdates];
    NSMutableArray *indexPaths = [NSMutableArray arrayWithCapacity:[messages count]];
    for (id msg in messages) {
        [self.messagesaddObject:msg];
        NSIndexPath *indexPath = [NSIndexPath indexPathForRow:[self.messagescount] - 1
                                                    inSection:0];
        [indexPaths addObject:indexPath];
    }

    [self.tableView insertRowsAtIndexPaths:indexPaths
                          withRowAnimation:UITableViewRowAnimationAutomatic];
    [self.tableView endUpdates];
    [self scrollToBottomAnimated:YES];
}

- (BOOL)isOwnMessage:(NSCMessage *)message {
    return [message.userId isEqualToString:self.client.currentUser.userId];
}

- (BubbleMessageStyle)messageStyleForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSCMessage *msg = self.messages[indexPath.row];
    return [self isOwnMessage:msg] ? BubbleMessageStyleOutgoing : BubbleMessageStyleIncoming;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    return [self.messages count];
}

- (NSString *)textForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSCMessage *msg = self.messages[indexPath.row];
    if ([selfisOwnMessage:msg]) {
        return msg.text;
    }

    NSString *text = [NSStringstringWithFormat:@"%@\n\n--%@", msg.text, msg.author];
    return text;
}

- (void)insertMessageRow:(NSCMessage *)msg {
    [self.messages addObject:msg];
    NSIndexPath *indexPath = [NSIndexPath indexPathForRow:([self.messages count] - 1) inSection:0];
    [self.tableView insertRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationAutomatic];
}

## Sending Messages

- (void)sendPressed:(UIButton *)sender withText:(NSString *)text {
    sender.enabled = NO;

    NSCMessage *newMessage = [[NSCMessage alloc] init];
    newMessage.text = text;
    newMessage.roomId = self.room.roomId;

    [[self messagesTable] insert:[newMessage attributes]
                      completion:^(NSDictionary *item, NSError *error) {
                          if (item) {
                              NSCMessage *insertedMessage = [NSCMessage messageWithDictionary:item];
                              [self insertMessageRow:insertedMessage];
                              [self finishSend];
                          } else {
                              NSLog(@"ERROR: %@", error);
                              [[[UIAlertView alloc] initWithTitle:@"Didn't post your message"
                                                          message:[error localizedDescription]
                                                         delegate:nil
                                                cancelButtonTitle:@"OK"
                                                otherButtonTitles:nil] show];
                          }
                      }];
}

Server side script for inserting new messages & inserting push notifications

This goes on Messages -> Insert.

function insert(item, user, request) {
    item.createdAt = new Date();
    item.userId = user.userId;
    request.execute({
        success: function() {
            sendPushNotification(item);
            request.respond();
        }
    });   
}


function sendPushNotification(item) {
    var users = tables.getTable("Users");
    users.where({ roomId: item.roomId }).read({
        success: function(results) {
            results.forEach(function(u) {
                // don't send it to the sender
                if (u.userId == item.userId) return;

                // don't send it if we don't have a device token
                if (u.deviceToken === null) return;

                console.log("User: ", u);
                push.apns.send(u.deviceToken, {
                    alert: item.text,
                    payload: {
                        roomId: item.roomId
                    }
                });
            });
        }
    });
}

Reading the messages and including the username in the response

In the Messages table, Read script:

function getUsers(ids, callback) {
    var users = tables.getTable("Users");
    users.where(function(ids) {
        return this.userId in ids;
    }, ids).read({
        success: function(results) {
            callback(results);
        }
    });
}


function read(query, user, request) {
    request.execute({
        success: function(msgResults, error) {
            var userIds = msgResults.map(function(r) {
                return r.userId;
            });

            if (userIds !== undefined && userIds.length > 0) {
                console.log("User ids: " + userIds);
                getUsers(userIds, function(userResults) {
                    msgResults.forEach(function(msg) {
                        var user = userResults.filter(function(u) { return u.userId == msg.userId })[0];
                        msg.author = user.username;
                    });

                    request.respond();
                });
            } else {
                request.respond();
            }

        }
    });
}

Polling for changes

- (void)startPolling {
    // don't poll if the current device is using push notifications
    if ([[NSUserDefaults standardUserDefaults] objectForKey:@"deviceToken"]) {
        return;
    }

    self.fetchTimer = [NSTimer scheduledTimerWithTimeInterval:10
                                                       target:self
                                                     selector:@selector(fetchMessages)
                                                     userInfo:nil
                                                      repeats:YES];
}

- (void)stopPolling {
    [self.fetchTimer invalidate];
    self.fetchTimer = nil;
}

Responding to push notifications

When we get a push notification, we'll publish an NSNotification including the room id so the view controller knows to refresh the view. We'll do this in the app delegate:

- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo {
    NSLog(@"Notification: %@", userInfo);
    NSNumber *roomId = userInfo[@"roomId"];
    [[NSNotificationCenter defaultCenter] postNotificationName:@"NSCMessageReceivedNotification"
                                                       object:roomId];
}

We listen for this notification in our NSCChatViewController. When it arrives, we check the room id and if the message is intended for this room we fetch messages again.

- (void)listenForMessages {
    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(onMessageReceived:)
                                                 name:@"NSCMessageReceivedNotification"
                                               object:nil];
}

- (void)onMessageReceived:(NSNotification *)notification {
    NSNumber *roomId = [notification object];
    if ([roomId intValue] == self.room.roomId) {
        [self fetchMessages];
    }
}