利用Multipeer Connectivity框架进行WiFi传输

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];
    }
}