Apple GameKit Bluetooth Integration Tutorial

The aim of this tutorial will be mainly to connect between 2 devices using Bluetooth – We will be using GKSession and GKPeerPickerController to get this done.

I will be writing another blog post where I will discuss more about how to connect more then 2 devices using GKSession.

Lets Start!

  • The aim of this project will be sending farts from one device to another – doesn’t matter if its a iPhone, iPod or iPad.
  • StartĀ  a new Xcode Project name it “SendFarts” – Use View-based applocation type

  • Add the GameKit Framework

  • We will be sending fart names, so we will have couple of buttonĀ  – “Loud Fart” and “Silent Assassin Fart”
  • Lets go to SendFartsViewController.h file and add the following code.
  • #import <UIKit/UIKit.h>
    // 1. Import the gamekit framework
    #import <GameKit/GameKit.h>
    // 2. Subclass to GKSessionDelegate and GKPeerPickerControllerDelegate
    //    GKSessionDelegate - Used to maintain Sessions
    //    GKPeerPickerControllerDelegate - Gives a apple provided peer picker,
    //            where you can look for other devcies using teh same apps to connect with
    @interface SendFartsViewController : UIViewController <GKSessionDelegate, GKPeerPickerControllerDelegate>{
    // 3. Create these folloeing for
    	// Session Object
    	GKSession *fartSession;
    	// PeerPicker Object
    	GKPeerPickerController *fartPicker;
    	// Array of peers connected
    	NSMutableArray *fartPeers;
    @property (retain) GKSession *fartSession;
    // 4.  Methods to connect and send data
    - (void) connectToPeers:(id) sender;
    - (void) sendALoudFart:(id)sender;
    - (void) sendASilentAssassin:(id)sender;
  • .The code above is quite explanatory with the comments I have added
  • Next, go to SendFartsViewController.m file and add the following code, follow the comments to see what I have done.
#import "SendFartsViewController.h"

@implementation SendFartsViewController

@synthesize fartSession;

- (void)viewDidLoad {
    [super viewDidLoad];

	fartPicker = [[GKPeerPickerController alloc] init];
	fartPicker.delegate = self;

	//There are 2 modes of connection type
	// - GKPeerPickerConnectionTypeNearby via BlueTooth
	// - GKPeerPickerConnectionTypeOnline via Internet
	// We will use Bluetooth Connectivity for this example

	fartPicker.connectionTypesMask = GKPeerPickerConnectionTypeNearby;
	fartPeers=[[NSMutableArray alloc] init];

	// Create the buttons
	UIButton *btnConnect = [UIButton buttonWithType:UIButtonTypeRoundedRect];
	[btnConnect addTarget:self action:@selector(connectToPeers:) forControlEvents:UIControlEventTouchUpInside];
	[btnConnect setTitle:@"Connect" forState:UIControlStateNormal];
	btnConnect.frame = CGRectMake(20, 100, 280, 30);
	btnConnect.tag = 12;
	[self.view addSubview:btnConnect];


// Connect to other peers by displayign the GKPeerPicker
- (void) connectToPeers:(id) sender{
	[fartPicker show];

- (void) sendALoudFart:(id)sender{
	// Making up the Loud Fart sound :P 
	NSString *loudFart = @"Brrrruuuuuummmmmmmppppppppp";

	// Send the fart to Peers using teh current sessions
	[fartSession sendData:[loudFart dataUsingEncoding: NSASCIIStringEncoding] toPeers:fartPeers withDataMode:GKSendDataReliable error:nil];


- (void) sendASilentAssassin:(id)sender{
	// Making up the Silent Assassin :P 
	NSString *silentAssassin = @"Puuuuuuuusssssssssssssssss";

	// Send the fart to Peers using teh current sessions
	[fartSession sendData:[silentAssassin dataUsingEncoding: NSASCIIStringEncoding] toPeers:fartPeers withDataMode:GKSendDataReliable error:nil];


- (void)dealloc {
	[fartPeers release];
    [super dealloc];

#pragma mark -
#pragma mark GKPeerPickerControllerDelegate

// This creates a unique Connection Type for this particular applictaion
- (GKSession *)peerPickerController:(GKPeerPickerController *)picker sessionForConnectionType:(GKPeerPickerConnectionType)type{
	// Create a session with a unique session ID - displayName:nil = Takes the iPhone Name
	GKSession* session = [[GKSession alloc] initWithSessionID:@"com.vivianaranha.sendfart" displayName:nil sessionMode:GKSessionModePeer];
    return [session autorelease];

// Tells us that the peer was connected
- (void)peerPickerController:(GKPeerPickerController *)picker didConnectPeer:(NSString *)peerID toSession:(GKSession *)session{

	// Get the session and assign it locally
    self.fartSession = session;
    session.delegate = self;

    //No need of teh picekr anymore
	picker.delegate = nil;
    [picker dismiss];
    [picker autorelease];

// Function to receive data when sent from peer
- (void)receiveData:(NSData *)data fromPeer:(NSString *)peer inSession: (GKSession *)session context:(void *)context
	//Convert received NSData to NSString to display
   	NSString *whatDidIget = [[NSString alloc] initWithData:data encoding:NSASCIIStringEncoding];

	//Dsiplay the fart as a UIAlertView
	UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Fart Received" message:whatDidIget delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
	[alert show];
	[alert release];
	[whatDidIget release];

#pragma mark -
#pragma mark GKSessionDelegate

- (void)session:(GKSession *)session peer:(NSString *)peerID didChangeState:(GKPeerConnectionState)state{

	if(state == GKPeerStateConnected){
		// Add the peer to the Array
		[fartPeers addObject:peerID];

		NSString *str = [NSString stringWithFormat:@"Connected with %@",[session displayNameForPeer:peerID]];
		UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Connected" message:str delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil];
		[alert show];
		[alert release];

		// Used to acknowledge that we will be sending data
		[session setDataReceiveHandler:self withContext:nil];

		[[self.view viewWithTag:12] removeFromSuperview];

		UIButton *btnLoudFart = [UIButton buttonWithType:UIButtonTypeRoundedRect];
		[btnLoudFart addTarget:self action:@selector(sendALoudFart:) forControlEvents:UIControlEventTouchUpInside];
		[btnLoudFart setTitle:@"Loud Fart" forState:UIControlStateNormal];
		btnLoudFart.frame = CGRectMake(20, 150, 280, 30);
		btnLoudFart.tag = 13;
		[self.view addSubview:btnLoudFart];

		UIButton *btnSilentFart = [UIButton buttonWithType:UIButtonTypeRoundedRect];
		[btnSilentFart addTarget:self action:@selector(sendASilentAssassin:) forControlEvents:UIControlEventTouchUpInside];
		[btnSilentFart setTitle:@"Silent Assassin" forState:UIControlStateNormal];
		btnSilentFart.frame = CGRectMake(20, 200, 280, 30);
		btnSilentFart.tag = 14;
		[self.view addSubview:btnSilentFart];


  • Build and run. Now you can also send farts through Bluetooth – Technology, what can I say about it.
  • Download the application HERE

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