1. EEC-492/693/793 iPhone Application Development
Lecture 15
Wenbing Zhao & Nigamanth Sridhar
2/16/2019
EEC492/693/793 - iPhone Application Development

2. Outline Peer-to-Peer Communication with GameKit Demo Assignment:
GKPeerPickerController & GKPeerPickerControllerDelegate
GKSession & GKSessionDelegate
Objects  NSData
Demo
Assignment:
Build the chat app using the GameKit
Challenge: enable 3 or more peers to chat together
Documentation on GameKit:
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2/16/2019
EEC492/693/793 - iPhone Application Development
EEC492/693/793 - iPhone Application Development 2

3. EEC492/693/793 - iPhone Application Development
Game Kit
Introduced in iOS 3.0 to enable the development of social games
Game Kit consists of three technologies:
Game center: centralized network service (supported in iOS 4.1 and later)
Peer-to-peer networking (supported in iOS 3.0 and later)
In-game voice chat (supported in iOS 3.0 and later)
2/16/2019
EEC492/693/793 - iPhone Application Development

4. Peer-to-Peer Connectivity
Abstracts away Bonjour and Stream creation
Nearby (Bluetooth) & Online (Wifi) support
2/16/2019
EEC492/693/793 - iPhone Application Development

5. Peer-to-Peer Connectivity
Peer discovery: GKPeerPickerController
The GKPeerPickerController presents the UI and responds to the user’s actions
Resulting in a fully configured GKSession that connects two peers
Peer communication: GKSession
2/16/2019
EEC492/693/793 - iPhone Application Development

6. GKPeerPickerController
Provides UI to connect to peer
Allows user to pick between “Nearby” and “Online”
Nearby
Bluetooth communication
Most of the work is handled for you under-the-hood
Online
Hands off responsibility to the application
App builds or connects to server
Associates users in server
App is responsible for handling communication
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EEC492/693/793 - iPhone Application Development

7. Initiating a Connection
// Allocate the PeerPickerController
GKPeerPickerController *peerPicker;
peerPicker = [[GKPeerPickerController alloc] init];
// Set up delegate to receive callbacks
peerPicker.delegate = self;
peerPicker.connectionMask =
GKPeerPickerConnectionTypeOnline |
GKPeerPickerConnectionTypeNearby;
// Display the Peer Picker
[peerPicker show];
2/16/2019
EEC492/693/793 - iPhone Application Development

8. Establishing a Connection
Return a session for the requested type (by the GKPeerPickerControllerDelegate) (called when you chose “Nearby”)
- (GKSession *)peerPickerController: (GKPeerPickerController *)picker
sessionForConnectionType: (GKPeerPickerConnectionType)type {
GKSession *session = [[GKSession alloc] initWithSessionID:nil
displayName:localName sessionMode:GKSessionModePeer];
return [session autorelease]; }
Accept connection request from the remote peer (by the GKSession delegate)
- (void)session:(GKSession *)session
didReceiveConnectionRequestFromPeer:(NSString *)peerID {
[session acceptConnectionFromPeer:peerID error:nil];
2/16/2019
EEC492/693/793 - iPhone Application Development

9. Establishing a Connection
Notification to the requesting peer on the establishment of the connection
- (void) peerPickerController:(GKPeerPickerController *)picker didConnectPeer:(NSString *)peerID toSession:(GKSession *)session {
session.delegate = self;
[session setDataReceiveHandler:self withContext:nil];
self.gameSession = session; …
// Done with the Peer Picker so dismiss it
[picker dismiss];
[picker autorelease]; }
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EEC492/693/793 - iPhone Application Development

10. Other GKPeerPickerControllerDelegate Methods
- (void) peerPickerController:(GKPeerPickerController *)picker didSelectConnectionType:(GKPeerPickerConnectionType)type
Should dismiss picker if the type is GKPeerPickerConnectionTypeOnline, and provide your own UI
- (void) peerPickerControllerDidCancel:(GKPeerPickerController *)picker
Do some cleaning up, if necessary
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EEC492/693/793 - iPhone Application Development

11. EEC492/693/793 - iPhone Application Development
GKSession
Creating a GKSession
GKSession *session = [[GKSession alloc] initWithSessionID:…
- (id)initWithSessionID:(NSString *)sessionID
displayName:(NSString *)name
sessionMode:(GKSessionMode)mode
typedef enum {
GKSessionModeServer,
GKSessionModeClient,
GKSessionModePeer
} GKSessionMode;
2/16/2019
EEC492/693/793 - iPhone Application Development

12. EEC492/693/793 - iPhone Application Development
GKSession
Properties include:
displayName - Your name, as seen by your peers
peerID - unique ID, identifying your Session to your peers
sessionID - String used by your Application to filter peers
available – determines whether or not the session wants to connect to new peers
Delegate methods:
Notifies of state change of a peer’s session
Notifies of connection requests
Notifies of errors with sessions or connections
2/16/2019
EEC492/693/793 - iPhone Application Development

13. GKSession - Sending & Receiving Data
Send data to specific peers
- (BOOL) sendData:(NSData *)data toPeers:(NSArray *)peers
withDataMode:(GKSendDataMode)mode error:(NSError **)error;
Data transmission mode:
GKSendDataReliable, GKSendDataUnreliable
Send data to ALL connected peers
- (BOOL) sendDataToAllPeers:(NSData *)data withDataMode:
(GKSendDataMode)mode error:(NSError **)error;
Data handler method to receive data:
- (void) receiveData:(NSData *)data fromPeer:(NSString *)peer
inSession:(GKSession *)session context:(void *)context;
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EEC492/693/793 - iPhone Application Development

14. How to Pack Data into NSData
From NSString to NSData
NSData *data = [msgToSend.text dataUsingEncoding:NSUTF8StringEncoding];
From NSData to NSString
NSString *recvStr = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
For more complicated data, can use Archiver
// Objects to NSData
NSMutableArray *touchesForUser = …;
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:touchesForUser];
// NSData to objects
NSMutableArray *touchValues = [[NSKeyedUnarchiver unarchiveObjectWithData:data] mutableCopy];
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EEC492/693/793 - iPhone Application Development