Come check out Multi-Peer Connectivity, a brand new framework for connecting multiple devices in a peer-to-peer network. We'll learn how to get a basic application up and running and take advantage of these new APIs to create a whole new interactive dynamic in your apps.

1. Multi-Peer Connectivity

2. Architecture

3. Multi-Peer Connectivity
•
New in iOS 7
•
Ability to connect to a mesh of peers.
•
Able to connect to peers over WiFi, ad-hoc wireless, and Bluetooth.
•
Peers must be ‘nearby’.

4. Terms
•
Advertiser - Broadcasts availability to connect
•
Browser - Invites advertisers to join a session

5. MCSession
•
MCSession manages all communication between peers.
•
Must be used by all participants.

6. Create A Session
self.peerID = [[MCPeerID alloc] initWithDisplayName:@"Jill"];
!
self.currentSession = [[MCSession alloc] initWithPeer:self.peerID];
self.currentSession.delegate = self;

7. Discovery
Browser
Advertiser
Advertiser
Who wants to
chat?
Ready to
chat!
Ready to
chat!

8. Advertising
self.peerID = [[MCPeerID alloc] initWithDisplayName:@"Jill"];
!
self.advertiser = [[MCNearbyServiceAdvertiser alloc] initWithPeer:self.peerID
discoveryInfo:nil
serviceType:@"whartman-chat"];
self.advertiser.delegate = self;
[self.advertiser startAdvertisingPeer];

9. Browsing
self.peerID = [[MCPeerID alloc] initWithDisplayName:@"Jack"];
!
self.browser = [[MCNearbyServiceBrowser alloc] initWithPeer:self.peerID
serviceType:@"whartman-chat"];
self.browser.delegate = self;
[self.browser startBrowsingForPeers];

10. Browser: Discover & Invite
- (void)browser:(MCNearbyServiceBrowser *)browser foundPeer:(MCPeerID *)peerID
withDiscoveryInfo:(NSDictionary *)info
{
[browser invitePeer:peerID
toSession:self.currentSession
withContext:nil
timeout:3.0];
}

11. Advertiser: Accept Invitation
- (void)advertiser:(MCNearbyServiceAdvertiser *)advertiser didReceiveInvitationFromPeer:
(MCPeerID *)peerID withContext:(NSData *)context invitationHandler:(void(^)(BOOL accept,
MCSession *session))invitationHandler
{
// In most cases you will want to give users an option to connect or not.
invitationHandler(YES, self.currentSession);
[self.advertiser stopAdvertisingPeer]; // Once invited, stop advertising
}

12. Sending Data To Peers
NSDictionary *message = @{ @"message" : @"Hello!" };
NSData *messageData = [NSJSONSerialization dataWithJSONObject:message options:0 error:nil];
!
NSError *error = nil;
!
[self.currentSession sendData:messageData
toPeers:self.currentSession.connectedPeers
withMode:MCSessionSendDataReliable
error:&error];

13. Receiving Data From Peers
- (void)session:(MCSession *)session didReceiveData:(NSData *)data fromPeer:(MCPeerID *)peerID {
NSError *error = nil;
!
NSDictionary *recievedData = [NSJSONSerialization JSONObjectWithData:data
options:0
error:&error];
!
if (!recievedData) {
NSLog(@"error decoding message! %@", error);
} else {
// Display message to the user...
}
}

14. Sending Resources To Peers
NSString *filePath = [[NSBundle mainBundle] pathForResource:@"hello" ofType:@"jpg"];
NSURL *imageURL = [NSURL fileURLWithPath:filePath];
!
[self.currentSession sendResourceAtURL:imageURL
withName:@"hello.jpg"
toPeer:peer
withCompletionHandler:^(NSError *error) {
if (error) {
NSLog(@"Error sending image! %@", error);
}
}];

15. Receiving Resources From Peers
- (void)session:(MCSession *)session didStartReceivingResourceWithName:(NSString *)resourceName
fromPeer:(MCPeerID *)peerID withProgress:(NSProgress *)progress {
NSLog(@"downloading file: %f%%", progress.fractionCompleted);
}
!
!
!
!
- (void)session:(MCSession *)session didFinishReceivingResourceWithName:(NSString *)resourceName
fromPeer:(MCPeerID *)peerID atURL:(NSURL *)localURL withError:(NSError *)error {
!
if (error) {
NSLog(@"Error when receiving file! %@", error);
} else {
// Present the resource to the user.
}
}

16. Demo

17. Best Practices
•
Keep messages short.
•
Be careful with inviting/accept invitations.
•
As an advertiser, once you have accepted an invitation, stop advertising.

18. Limitations
•
Limit to 8 connected peers.
•
Data transfer is slow—especially on Bluetooth.

19. Questions?

20. Resources
•
Nearby Networking with Multipeer Connectivity (WWDC 2013)
•
Demo App - https://github.com/waynehartman/MultiPeerTest/