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作者:小馬

IOS學習也一段時間了，該上點干貨了。前段時間研究了一下IOS藍牙通訊相關的東西，把研究的一個成果給大家分享一下。

一 項目背景

簡單介紹一下做的東西，設備是一個金融刷卡器，通過藍牙與iphone手機通訊。手機端的app通過發送不同的指令(通過藍牙)控制刷卡器執行一些動作，比如讀磁條卡，讀金融ic卡等。上幾張圖容易理解一些：

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看了上面幾張圖，你應該大概了解這是個什么東東了。

二 IOS 藍牙介紹

藍牙協議本身經歷了從1.0到4.0的升級演變, 最新的4.0以其低功耗著稱，所以一般也叫BLE(Bluetoothlow energy)。

iOS 有兩個框架支持藍牙與外設連接。一個是 ExternalAccessory。從ios3.0就開始支持，也是在iphone4s出來之前用的比較多的一種模式，但是它有個不好的地方，External Accessory需要拿到蘋果公司的MFI認證。

另一個框架則是本文要介紹的CoreBluetooth,在iphone4s開始支持,專門用于與BLE設備通訊（因為它的API都是基于BLE的）。這個不需要MFI，并且現在很多藍牙設備都支持4.0,所以也是在IOS比較推薦的一種開發方法。

三 CoreBluetooth介紹

CoreBluetooth框架的核心其實是兩個東西，peripheral和central, 可以理解成外設和中心。對應他們分別有一組相關的API和類，如下圖所示:

如果你要編程的設備是central那么你大部分用到，反之亦然。在我們這個示例中，金融刷卡器是peripheral,我們的iphone手機是central,所以我將大部分使用上圖中左邊部分的類。使用peripheral編程的例子也有很多，比如像用一個ipad和一個iphone通訊，ipad可以認為是central，iphone端是peripheral,這種情況下在iphone端就要使用上圖右邊部分的類來開發了。

四 服務和特征

有個概念有必要先說明一下。什么是服務和特征呢(service and characteristic)?

每個藍牙4.0的設備都是通過服務和特征來展示自己的，一個設備必然包含一個或多個服務，每個服務下面又包含若干個特征。特征是與外界交互的最小單位。比如說，一臺藍牙4.0設備，用特征A來描述自己的出廠信息，用特征B來與收發數據等。

服務和特征都是用UUID來唯一標識的，UUID的概念如果不清楚請自行google,國際藍牙組織為一些很典型的設備(比如測量心跳和血壓的設備)規定了標準的service UUID(特征的UUID比較多，這里就不列舉了),如下:

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#define????? BLE_UUID_ALERT_NOTIFICATION_SERVICE?? 0x1811 ?#define???? BLE_UUID_BATTERY_SERVICE?? 0x180F ?#define???? BLE_UUID_BLOOD_PRESSURE_SERVICE?? 0x1810 ?#define???? BLE_UUID_CURRENT_TIME_SERVICE?? 0x1805 ?#define???? BLE_UUID_CYCLING_SPEED_AND_CADENCE?? 0x1816 ?#define???? BLE_UUID_DEVICE_INFORMATION_SERVICE?? 0x180A ?#define???? BLE_UUID_GLUCOSE_SERVICE?? 0x1808 ?#define???? BLE_UUID_HEALTH_THERMOMETER_SERVICE?? 0x1809 ?#define???? BLE_UUID_HEART_RATE_SERVICE?? 0x180D ?#define???? BLE_UUID_HUMAN_INTERFACE_DEVICE_SERVICE?? 0x1812 ?#define???? BLE_UUID_IMMEDIATE_ALERT_SERVICE?? 0x1802 ?#define???? BLE_UUID_LINK_LOSS_SERVICE?? 0x1803 ?#define???? BLE_UUID_NEXT_DST_CHANGE_SERVICE?? 0x1807 ?#define???? BLE_UUID_PHONE_ALERT_STATUS_SERVICE?? 0x180E ?#define???? BLE_UUID_REFERENCE_TIME_UPDATE_SERVICE?? 0x1806 ?#define???? BLE_UUID_RUNNING_SPEED_AND_CADENCE?? 0x1814 ?#define???? BLE_UUID_SCAN_PARAMETERS_SERVICE?? 0x1813 ?#define???? BLE_UUID_TX_POWER_SERVICE?? 0x1804 ?#define???? BLE_UUID_CGM_SERVICE?? 0x181A

當然還有很多設備并不在這個標準列表里，比如我用的這個金融刷卡器。藍牙設備硬件廠商通常都會提供他們的設備里面各個服務(service)和特征(characteristics)的功能，比如哪些是用來交互(讀寫)，哪些可獲取模塊信息(只讀)等。

五 實現細節

作為一個中心要實現完整的通訊，一般要經過這樣幾個步驟：

建立中心角色—掃描外設（discover）—連接外設(connect)—掃描外設中的服務和特征(discover)—與外設做數據交互(explore and interact)—斷開連接(disconnect)。

1建立中心角色

首先在我自己類的頭文件中要包含CoreBluetooth的頭文件，并繼承兩個協議，代碼如下:

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#import <corebluetooth corebluetooth.h=""> CBCentralManager *manager; manager = [[CBCentralManager alloc] initWithDelegate:self queue:nil];</corebluetooth>

2掃描外設（discover）

代碼如下:

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1	[manager scanForPeripheralsWithServices:nil options:options];

這個參數應該也是可以指定特定的peripheral的UUID,那么理論上這個central只會discover這個特定的設備，但是我實際測試發現，如果用特定的UUID傳參根本找不到任何設備，我用的代碼如下:

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NSArray *uuidArray = [NSArray arrayWithObjects:[CBUUID UUIDWithString:@"1800"],[CBUUID UUIDWithString:@"180A"], [CBUUID UUIDWithString:@"1CB2D155-33A0-EC21-6011-CD4B50710777"],[CBUUID UUIDWithString:@"6765D311-DD4C-9C14-74E1-A431BBFD0652"],nil]; ?????? [manager scanForPeripheralsWithServices:uuidArray options:options];

目前不清楚原因，懷疑和設備本身在的廣播包有關。

3連接外設(connect)

當掃描到4.0的設備后，系統會通過回調函數告訴我們設備的信息，然后我們就可以連接相應的設備，代碼如下:

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- (void)centralManager:(CBCentralManager *)central didDiscoverPeripheral:(CBPeripheral *)peripheral advertisementData:(NSDictionary *)advertisementData RSSI:(NSNumber *)RSSI { ????if(![_dicoveredPeripherals containsObject:peripheral]) ????????[_dicoveredPeripherals addObject:peripheral]; ????? ????NSLog(@"dicoveredPeripherals:%@", _dicoveredPeripherals); }

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//連接指定的設備 -(BOOL)connect:(CBPeripheral *)peripheral { ????NSLog(@"connect start"); ????_testPeripheral = nil; ????? ????[manager connectPeripheral:peripheral ???????????????????????options:[NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:CBConnectPeripheralOptionNotifyOnDisconnectionKey]]; ????? ????//開一個定時器監控連接超時的情況 ????connectTimer = [NSTimer scheduledTimerWithTimeInterval:5.0f target:self selector:@selector(connectTimeout:) userInfo:peripheral repeats:NO]; ????return (YES); }

4掃描外設中的服務和特征(discover)

同樣的，當連接成功后，系統會通過回調函數告訴我們，然后我們就在這個回調里去掃描設備下所有的服務和特征，代碼如下:

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- (void)centralManager:(CBCentralManager *)central didConnectPeripheral:(CBPeripheral *)peripheral { ????[connectTimer invalidate];//停止時鐘 ????? ????NSLog(@"Did connect to peripheral: %@", peripheral); ????_testPeripheral = peripheral; ????? ????[peripheral setDelegate:self]; ????[peripheral discoverServices:nil]; ????? ????? }

一個設備里的服務和特征往往比較多，大部分情況下我們只是關心其中幾個，所以一般會在發現服務和特征的回調里去匹配我們關心那些，比如下面的代碼:

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- (void)peripheral:(CBPeripheral *)peripheral didDiscoverServices:(NSError *)error { ????? ????NSLog(@"didDiscoverServices"); ????? ????if (error) ????{ ????????NSLog(@"Discovered services for %@ with error: %@", peripheral.name, [error localizedDescription]); ????????? ????????if ([self.delegate respondsToSelector:@selector(DidNotifyFailConnectService:withPeripheral:error:)]) ????????????[self.delegate DidNotifyFailConnectService:nil withPeripheral:nil error:nil]; ????????? ????????return; ????} ????? ????for (CBService *service in peripheral.services) ????{ ????????? ????????if ([service.UUID isEqual:[CBUUID UUIDWithString:UUIDSTR_ISSC_PROPRIETARY_SERVICE]]) ????????{ ????????????NSLog(@"Service found with UUID: %@", service.UUID); ????????????[peripheral discoverCharacteristics:nil forService:service]; ????????????isVPOS3356 = YES; ????????????break; ????????} ????????? ????????? ????} }

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- (void)peripheral:(CBPeripheral *)peripheral didDiscoverCharacteristicsForService:(CBService *)service error:(NSError *)error { ????? ????if (error) ????{ ????????NSLog(@"Discovered characteristics for %@ with error: %@", service.UUID, [error localizedDescription]); ????????? ????????if ([self.delegate respondsToSelector:@selector(DidNotifyFailConnectChar:withPeripheral:error:)]) ????????????[self.delegate DidNotifyFailConnectChar:nil withPeripheral:nil error:nil]; ????????? ????????return; ????} ????? ????? ????for (CBCharacteristic *characteristic in service.characteristics) ????{ ????????if ([characteristic.UUID isEqual:[CBUUID UUIDWithString:UUIDSTR_ISSC_TRANS_TX]]) ????????{ ????????????NSLog(@"Discovered read characteristics:%@ for service: %@", characteristic.UUID, service.UUID); ????????????? ????????????_readCharacteristic = characteristic;//保存讀的特征 ????????????? ????????????if ([self.delegate respondsToSelector:@selector(DidFoundReadChar:)]) ????????????????[self.delegate DidFoundReadChar:characteristic]; ????????????? ????????????break; ????????} ????} ????? ????for (CBCharacteristic * characteristic in service.characteristics) ????{ ????????? ????????? ????????if ([characteristic.UUID isEqual:[CBUUID UUIDWithString:UUIDSTR_ISSC_TRANS_RX]]) ????????{ ????????????NSLog(@"Discovered write characteristics:%@ for service: %@", characteristic.UUID, service.UUID); ????????????_writeCharacteristic = characteristic;//保存寫的特征 ????????????? ????????????if ([self.delegate respondsToSelector:@selector(DidFoundWriteChar:)]) ????????????????[self.delegate DidFoundWriteChar:characteristic]; ????????????? ????????????break; ????????????? ????????????? ????????} ????} ????? ????if ([self.delegate respondsToSelector:@selector(DidFoundCharacteristic:withPeripheral:error:)]) ????????[self.delegate DidFoundCharacteristic:nil withPeripheral:nil error:nil]; ????? }

相信你應該已經注意到了，回調函數都是以"did"開頭的，這些函數不用你調用，達到條件后系統后自動調用。

5與外設做數據交互(explore and interact)

發送數據很簡單，我們可以封裝一個如下的函數:

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//寫數據 -(void)writeChar:(NSData *)data { ????[_testPeripheral writeValue:data forCharacteristic:_writeCharacteristic type:CBCharacteristicWriteWithResponse]; }

_testPeripheral和_writeCharacteristic是前面我們保存的設備對象和可以讀寫的特征。

然后我們可以在外部調用它，比如當然我要觸發刷卡時，先組好數據包，然后調用發送函數:

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-(void)msrRead { ????? ????unsigned char command[512] = {0}; ????unsigned char *pTmp; ????int nSendLen = 0; ????unsigned char ucCrc[3] = {0}; ????? ????_commandType = COMMAND_MSR_READ; ????? ????pTmp = command; ????? ????? ????*pTmp = 0x02;//start ????pTmp++; ????? ????*pTmp = 0xc1;//main cmd ????pTmp++; ????? ????*pTmp = 0x07;//sub cmd ????pTmp++; ????? ????? ????? ????nSendLen = 2; ????? ????*pTmp = nSendLen/256; ????pTmp++; ????*pTmp = nSendLen%256; ????pTmp++; ????? ????*pTmp = 0x00;//sub cmd ????pTmp++; ????? ????*pTmp = 0x00;//sub cmd ????pTmp++; ????? ????? ????Crc16CCITT(command+1,pTmp-command-1,ucCrc); ????memcpy(pTmp,ucCrc,2); ????? ????? ????NSData *data = [[NSData alloc] initWithBytes:&command length:9]; ????NSLog(@"send data:%@", data); ????[g_BLEInstance.recvData setLength:0]; ????? ????[g_BLEInstance writeChar:data]; }

數據的讀分為兩種，一種是直接讀(reading directly),另外一種是訂閱(subscribe)。從名字也能基本理解兩者的不同。實際使用中具體用一種要看具體的應用場景以及特征本身的屬性。前一個好理解，特征本身的屬性是指什么呢？特征有個properties字段(characteristic.properties),它是一個整型值,有如下幾個定義:

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enum { ?????CBCharacteristicPropertyBroadcast = 0x01, ?????CBCharacteristicPropertyRead = 0x02, ?????CBCharacteristicPropertyWriteWithoutResponse = 0x04, ?????CBCharacteristicPropertyWrite = 0x08, ?????CBCharacteristicPropertyNotify = 0x10, ?????CBCharacteristicPropertyIndicate = 0x20, ?????CBCharacteristicPropertyAuthenticatedSignedWrites = 0x40, ?????CBCharacteristicPropertyExtendedProperties = 0x80, ?????};

比如說，你要交互的特征，它的properties的值是0x10,表示你只能用訂閱的方式來接收數據。我這里是用訂閱的方式，啟動訂閱的代碼如下:

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//監聽設備 -(void)startSubscribe { ????[_testPeripheral setNotifyValue:YES forCharacteristic:_readCharacteristic]; }

當設備有數據返回時，同樣是通過一個系統回調通知我，如下所示:

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- (void)peripheral:(CBPeripheral *)peripheral didUpdateValueForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error { ????????? ????if (error) ????{ ????????NSLog(@"Error updating value for characteristic %@ error: %@", characteristic.UUID, [error localizedDescription]); ????????? ????????if ([_mainMenuDelegate respondsToSelector:@selector(DidNotifyReadError:)]) ????????????[_mainMenuDelegate DidNotifyReadError:error]; ????????? ????????return; ????} ????? ????[_recvData appendData:characteristic.value]; ????? ????? ????if ([_recvData length] >= 5)//已收到長度 ????{ ????????unsigned char *buffer = (unsigned char *)[_recvData bytes]; ????????int nLen = buffer[3]*256 + buffer[4]; ????????if ([_recvData length] == (nLen+3+2+2)) ????????{ ????????????//接收完畢，通知代理做事 ????????????if ([_mainMenuDelegate respondsToSelector:@selector(DidNotifyReadData)]) ????????????????[_mainMenuDelegate DidNotifyReadData]; ????????????? ????????} ????} }

6 斷開連接(disconnect)

這個比較簡單，只需要一個API就行了,代碼如下:

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//主動斷開設備 -(void)disConnect { ????? ????if (_testPeripheral != nil) ????{ ????????NSLog(@"disConnect start"); ????????[manager cancelPeripheralConnection:_testPeripheral]; ????} }

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