前一段时间，做了给lightning耳机升级的软件，现在抽空将其记录下来。
因为该软件涉及到MFI认证，所以需要External Accessory Framework框架。External Accessory Framework提供了配件连接iOS设备的通道。开发者可以通过它来开发连接配件的app。

下面就开始简单了解下External Accessory Framework都有些什么吧：

1. 它包含三个类：
   EAAccessory：代表了一个单例的硬件配件对象。
   EAAccessoryManager： 管理所有连接到iPhone的配件。
   EASession：定义了iPhone app与外部配件的连接和通道。

2. EAAccessory类
   EAAccessory类的属性:
   1 ）配件是否连接iPhone的标志
   @property(nonatomic, readonly, getter=isConnected) BOOL connected
   2 ）连接设备的配件唯一标识
   @property(nonatomic, readonly) NSUInteger connectionID
   3 ）配件的制造商
   @property(nonatomic, readonly) NSString *manufacturer
   4 ）配件名称
   @property(nonatomic, readonly) NSString *name
   5 ）配件型号
   @property(nonatomic, readonly) NSString *modelNumber
   6 ）配件序列号
   @property(nonatomic, readonly) NSString *serialNumber
   7 ）配件的固件版本号
   @property(nonatomic, readonly) NSString *firmwareRevision
   8 ）配件的硬件版本号
   @property(nonatomic, readonly) NSString *hardwareRevision

3. EAAccessoryManager
   //获取配件的所有信息
   NSMutableArray *accessoryList = [[NSMutableArray alloc] initWithArray:[[EAAccessoryManager sharedAccessoryManager] connectedAccessories]];
   比如：获取配件名称
   NSString *name = [accessoryList[0] name];

4. EASession
   // open a session with the accessory and set up the input and output stream on the default run loop
   - (BOOL)openSession
   {
   [_accessory setDelegate:self];
   _session = [[EASession alloc] initWithAccessory:_accessory forProtocol:_protocolString];

       if (_session)
       {
           [[_session inputStream] setDelegate:self];
           [[_session inputStream] scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
           [[_session inputStream] open];
   
           [[_session outputStream] setDelegate:self];
           [[_session outputStream] scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
           [[_session outputStream] open];
       }
       else
       {
           NSLog(@"creating session failed");
       }
   
       return (_session != nil);
   }
   

// close the session with the accessory.
- (void)closeSession
{
[[_session inputStream] close];
[[_session inputStream] removeFromRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[[_session inputStream] setDelegate:nil];
[[_session outputStream] close];
[[_session outputStream] removeFromRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
[[_session outputStream] setDelegate:nil];

        [_session release];
        _session = nil;

        [_writeData release];
        _writeData = nil;
        [_readData release];
        _readData = nil;
    }

// asynchronous NSStream handleEvent method
- (void)stream:(NSStream *)aStream handleEvent: (NSStreamEvent)eventCode
{
switch (eventCode) {
case NSStreamEventNone:
break;
case NSStreamEventOpenCompleted:
break;
case NSStreamEventHasBytesAvailable:
//TTSLOG(@"-----处理接收过来的数据包------");
[self _readData];
break;
case NSStreamEventHasSpaceAvailable:
[self _writeData];
break;
case NSStreamEventErrorOccurred:
//TTSLOG(@"----error-----");
break;
case NSStreamEventEndEncountered:
//TTSLOG(@"------end---------");
break;
default:
break;
}
}

5. 项目过程
   1 ）导入External Accessory Framework框架
   2 ）在info.plist里面添加协议，Supported external accessory protocols，协议名根厂家协商，例如：com.xxx.protocol
   3 ) 设置连接和断开连接通知
   [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(_accessoryDidConnect:) name:EAAccessoryDidConnectNotification object:nil];

   [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(_accessoryDidDisconnect:) name:EAAccessoryDidDisconnectNotification object:nil];
   
   [[EAAccessoryManager sharedAccessoryManager] registerForLocalNotifications];
   
   - (void)_accessoryDidConnect:(NSNotification *)notification {
   }
   
   - (void)_accessoryDidDisconnect:(NSNotification *)notification {
   }
   

4 ) 配件连接成功后获取配件对应的协议，创建一个accessory controller对象。
//注意：_selectedAccessory和PROTOCOLSTRING2协议要对应，不然是不会成功的；。
EADSessionController *_eaSessionController = [EADSessionController sharedController];

   [_eaSessionController setupControllerForAccessory:_selectedAccessory
                                       withProtocolString:PROTOCOLSTRING2];

5 ）打开session通讯
EADSessionController *sessionController = [EADSessionController sharedController];
_accessory = [sessionController accessory];
[sessionController openSession];
6 ）最后就是向配件发送指令，相关指令就与硬件工程师协商。

对于External Accessory Framework框架就先了解到这里，如有不解或者错误的地方，欢迎指出。