Peripheral.m

- (void)peripheralManager:(CBPeripheralManager *)peripheral
                  central:(CBCentral *)central
didSubscribeToCharacteristic:(CBCharacteristic *)characteristic {
    if (![self.centralM containsObject:central]) {
        [self.centralM addObject:central];
    }

    [self updateCharacteristicValue];
    [self stopAdvertising];
}

- (void)peripheralManager:(CBPeripheralManager *)peripheral
                  central:(CBCentral *)central
didUnsubscribeFromCharacteristic:(CBCharacteristic *)characteristic {
    [self startAdvertising];
}