什么是Multipeer Connectivity？
在iOS7中，引入了一个全新的框架——Multipeer Connectivity（多点连接）。利用Multipeer Connectivity框架，即使在没有连接到WiFi（WLAN）或移动网络（xG）的情况下，距离较近的Apple设备（iMac/iPad/iPhone）之间可基于蓝牙和WiFi（P2P WiFi）技术进行发现和连接实现近场通信。
Multipeer Connectivity扩充的功能与利用AirDrop传输文件非常类似，可以将其看作AirDrop不能直接使用的补偿，代价是需要自己实现。
本Demo主要用到4个类：
MCBrowserViewController:MCBrowserViewController继承自UIViewController，提供了基本的UI应用框架。
MCAdvertiserAssistant、MCAdvertiserAssistant为针对Advertiser封装的管理助手,主要处理广播信息。
MCSession:类似TCP链接中的socket。创建MCSession时，需指定自身MCPeerID，类似bind。
MCPeerID:类似sockaddr，用于标识连接的两端endpoint，通常是昵称或设备名称。
1、简单地建立一个界面，主要有连接和发送2个UIButton。
create_button.png
2、Multipeer Connectivity框架初始化这4个类。
#pragma mark - Wifi Sharing Methods-(void)setUpMultipeer{ // Setup peer ID self.myPeerID = [[MCPeerID alloc] initWithDisplayName:[UIDevice currentDevice].name]; // Setup session self.mySession = [[MCSession alloc] initWithPeer:self.myPeerID]; self.mySession.delegate = self; // Setup BrowserViewController self.browserVC = [[MCBrowserViewController alloc] initWithServiceType:@"chat" session:self.mySession]; self.browserVC.delegate = self; // Setup Advertiser self.advertiser = [[MCAdvertiserAssistant alloc] initWithServiceType:@"chat" discoveryInfo:nil session:self.mySession]; [self.advertiser start];}-(void)showBrowserVC{ [self presentViewController:self.browserVC animated:YES completion:nil];}-(void)dismissBrowserVC{ [self.browserVC dismissViewControllerAnimated:YES completion:^(void){ [self invokeAlertMethod:@"连接成功" Body:@"Both device connected successfully." Delegate:nil]; }];}-(void)stopWifiSharing:(BOOL)isClear{ if(isClear && self.mySession != nil){ [self.mySession disconnect]; [self.mySession setDelegate:nil]; self.mySession = nil; self.browserVC = nil; }} 3、MCBrowserViewController代理方法
#pragma marks MCBrowserViewControllerDelegate// 点击完成-(void)browserViewControllerDidFinish:(MCBrowserViewController *)browserViewController{ [self dismissBrowserVC]; [marrReceiveData removeAllObjects];}// 点击取消-(void)browserViewControllerWasCancelled:(MCBrowserViewController *)browserViewController{ [self dismissBrowserVC];} 4、MCSession代理方法
主要处理发送方传递的文件或者信息
// Received data from remote peer- (void)session:(MCSession *)session didReceiveData:(NSData *)data fromPeer:(MCPeerID *)peerID{ NSLog(@"data receiveddddd : %lu",(unsigned long)data.length); if (data.length > 0) { if (data.length < 2) { noOfDataSend++; NSLog(@"noofdatasend : %zd",noOfDataSend); NSLog(@"array count : %zd",marrFileData.count); if (noOfDataSend < ([marrFileData count])) { [self.mySession sendData:[marrFileData objectAtIndex:noOfDataSend] toPeers:[self.mySession connectedPeers] withMode:MCSessionSendDataReliable error:nil]; }else { [self.mySession sendData:[@"File Transfer Done" dataUsingEncoding:NSUTF8StringEncoding] toPeers:[self.mySession connectedPeers] withMode:MCSessionSendDataReliable error:nil]; } } else { if ([[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding] isEqualToString:@"File Transfer Done"]) { [self appendFileData]; }else { [self.mySession sendData:[@"1" dataUsingEncoding:NSUTF8StringEncoding] toPeers:[self.mySession connectedPeers] withMode:MCSessionSendDataReliable error:nil]; [marrReceiveData addObject:data]; } } }}// Received a byte stream from remote peer- (void)session:(MCSession *)session didReceiveStream:(NSInputStream *)stream withName:(NSString *)streamName fromPeer:(MCPeerID *)peerID{ NSLog(@"did receive stream");}// Start receiving a resource from remote peer- (void)session:(MCSession *)session didStartReceivingResourceWithName:(NSString *)resourceName fromPeer:(MCPeerID *)peerID withProgress:(NSProgress *)progress{ NSLog(@"start receiving");}// Finished receiving a resource from remote peer and saved the content in a temporary location - the app is responsible for moving the file to a permanent location within its sandbox- (void)session:(MCSession *)session didFinishReceivingResourceWithName:(NSString *)resourceName fromPeer:(MCPeerID *)peerID atURL:(NSURL *)localURL withError:(NSError *)error{ NSLog(@"finish receiving resource");}-(void)session:(MCSession *)session peer:(MCPeerID *)peerID didChangeState:(MCSessionState)state{ NSLog(@"change state : %zd",state);} 5、发送图片（此Demo只是简单地做了个收发图片的Demo，此框架可实现的功能当然不止这么简单。）
-(void)sendData{ [marrFileData removeAllObjects]; NSData *sendData = UIImagePNGRepresentation([UIImage imageNamed:@"test2.png"]); NSUInteger length = [sendData length]; NSUInteger chunkSize = 100 * 1024; NSUInteger offset = 0; do { NSUInteger thisChunkSize = length - offset > chunkSize ? chunkSize : length - offset; NSData* chunk = [NSData dataWithBytesNoCopy:(char *)[sendData bytes] + offset length:thisChunkSize freeWhenDone:NO]; NSLog(@"chunk length : %lu",(unsigned long)chunk.length); [marrFileData addObject:[NSData dataWithData:chunk]]; offset += thisChunkSize; } while (offset < length); noOfdata = [marrFileData count]; noOfDataSend = 0; if ([marrFileData count] > 0) { [self.mySession sendData:[marrFileData objectAtIndex:noOfDataSend] toPeers:[self.mySession connectedPeers] withMode:MCSessionSendDataReliable error:nil]; }}-(void)appendFileData{ NSMutableData *fileData = [NSMutableData data]; for (int i = 0; i < [marrReceiveData count]; i++) { [fileData appendData:[marrReceiveData objectAtIndex:i]]; } [fileData writeToFile:[NSString stringWithFormat:@"%@/Image.png", [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"]] atomically:YES]; UIImageWriteToSavedPhotosAlbum([UIImage imageWithData:fileData], self, @selector(image:didFinishSavingWithError:contextInfo:), nil);}- (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo{ if (!error) { [self invokeAlertMethod:@"发送成功" Body:@"图片已保存到手机相册" Delegate:nil]; }}