在 BLE 中，最常见的就是广播。实际上，peripheral 在不停的发送广播，希望被 central 找到。广播的信息中包含它的名字等信息。central 的作用则是去 scan，找到需要连接的 peripheral，连接后便可进行通信了。

[[CBCentralManager alloc] initWithDelegate:self queue:nil options:nil];

搜索当前可用的 peripheral

[myCentralManager scanForPeripheralsWithServices:nil options:nil];

- (void)centralManager:(CBCentralManager *)central
 didDiscoverPeripheral:(CBPeripheral *)peripheral
     advertisementData:(NSDictionary *)advertisementData
                  RSSI:(NSNumber *)RSSI {

    NSLog(@"Discovered %@", peripheral.name);
}

[myCentralManager stopScan];

连接 peripheral

[myCentralManager connectPeripheral:peripheral options:nil];

- (void)centralManager:(CBCentralManager *)central
  didConnectPeripheral:(CBPeripheral *)peripheral {

    NSLog(@"Peripheral connected");
}

搜索 peripheral 的 service

- (void)peripheral:(CBPeripheral *)peripheral
didDiscoverServices:(NSError *)error {

    for (CBService *service in peripheral.services) {
        NSLog(@"Discovered service %@", service);
    }
}

搜索 service 的 characteristic

[peripheral discoverCharacteristics:nil forService:interestingService]；

- (void)peripheral:(CBPeripheral *)peripheral
didDiscoverCharacteristicsForService:(CBService *)service
             error:(NSError *)error {

    for (CBCharacteristic *characteristic in service.characteristics) {
        NSLog(@"Discovered characteristic %@", characteristic);
    }
}

读取 characteristic 数据

NSLog(@"Reading value for characteristic %@", interestingCharacteristic);
[peripheral readValueForCharacteristic:interestingCharacteristic];

2、

- (void)peripheral:(CBPeripheral *)peripheral
didUpdateValueForCharacteristic:(CBCharacteristic *)characteristic
             error:(NSError *)error {

    NSData *data = characteristic.value;
    // parse the data as needed
}

订阅 Characteristic 数据

[peripheral setNotifyValue:YES forCharacteristic:interestingCharacteristic];

- (void)peripheral:(CBPeripheral *)peripheral
didUpdateNotificationStateForCharacteristic:(CBCharacteristic *)characteristic
             error:(NSError *)error {

    if (error) {
        NSLog(@"Error changing notification state: %@", [error localizedDescription]);
    }
}

当订阅成功以后，那数据便会实时的传回了，数据的回调依然和之前读取 characteristic 的回调相同（注意，不是订阅的那个回调）peripheral:didUpdateValueForCharacteristic:error:。

向 characteristic 写数据

[peripheral writeValue:dataToWrite forCharacteristic:interestingCharacteristic type:CBCharacteristicWriteWithResponse]；

- (void)peripheral:(CBPeripheral *)peripheral
didWriteValueForCharacteristic:(CBCharacteristic *)characteristic
             error:(NSError *)error {

    if (error) {
        NSLog(@"Error writing characteristic value: %@", [error localizedDescription]);
    }
}

检查设备是否能作为 central

centralManagerDidUpdateState

typedef NS_ENUM(NSInteger, CBCentralManagerState) {
    CBCentralManagerStateUnknown = 0,
    CBCentralManagerStateResetting,
    CBCentralManagerStateUnsupported,
    CBCentralManagerStateUnauthorized,
    CBCentralManagerStatePoweredOff,
    CBCentralManagerStatePoweredOn,
};

检查 characteristic 访问权限

CBCharacteristic的properties

typedef NS_OPTIONS(NSUInteger, CBCharacteristicProperties) {
    CBCharacteristicPropertyBroadcast                                               = 0x01,
    CBCharacteristicPropertyRead                                                    = 0x02,
    CBCharacteristicPropertyWriteWithoutResponse                                    = 0x04,
    CBCharacteristicPropertyWrite                                                   = 0x08,
    CBCharacteristicPropertyNotify                                                  = 0x10,
    CBCharacteristicPropertyIndicate                                                = 0x20,
    CBCharacteristicPropertyAuthenticatedSignedWrites                               = 0x40,
    CBCharacteristicPropertyExtendedProperties                                      = 0x80,
    CBCharacteristicPropertyNotifyEncryptionRequired NS_ENUM_AVAILABLE(NA, 6_0)     = 0x100,
    CBCharacteristicPropertyIndicateEncryptionRequired NS_ENUM_AVAILABLE(NA, 6_0)   = 0x200
};

多个权限可以通过|和&来判断是否支持，比如判断是否支持读或写：

BOOL isSupport = characteristic.properties & (CBCharacteristicPropertyRead | CBCharacteristicPropertyWrite)

写入后是否回调

[self.connectedPeripheral writeValue:data forCharacteristic:connectedCharacteristic type:CBCharacteristicWriteWithResponse]；

typedef NS_ENUM(NSInteger, CBCharacteristicWriteType) {
    CBCharacteristicWriteWithResponse = 0,
    CBCharacteristicWriteWithoutResponse,
};

- (void)peripheral:(CBPeripheral *)peripheral didWriteValueForCharacteristic:(CBCharacteristic *)characteristic error:(NSError *)error

CBCharacteristicPropertyNotify
Notifications of the characteristic’s value are permitted, without a response from the central to indicate that the notification was received.

Available in iOS 5.0 and later.
CBCharacteristicPropertyIndicate
Indications of the characteristic’s value are permitted, with a response from the central to indicate that the indication was received.

• ●  HFP using eSCO channel

• ●  A2DP using ACL channel