How to enable Indications on Client Configuration descriptor from iOS8 - ios

Question

I am trying to get the notification from a bluetooth device upon the characteristic value change. For this I need to enable notification for Client Characteristic Configuration(CCC) descriptor. I have used setNotifyValue(enabled: Bool, forCharacteristic characteristic: CBCharacteristic) for the characteristic but not getting the update for value changes.
I tried to enable the indication for CCC using writeValue(data: NSData, forDescriptor descriptor: CBDescriptor) but my app crashes for this API and shows the error as
Cannot write Client Characteristic Configuration descriptors using this method!
Any help!!

Answer 1

Provide more codes might help to imporove accuracy of an answer; however, let's be assuming you have already been able to discover all characteristic values. Usually you just need to iterate all characteristics and set/write value according to each Client Characteristic Configuration(CCC) descriptor in CBPeripheralDelegate implementation.
An example is attached below:
- (void)peripheral:(CBPeripheral *)peripheral didDiscoverCharacteristicsForService:(CBService *)service error:(NSError *)error
{
if (error) {
NSLog(#"Error discovering characteristics: %#", error);
return;
}
for (CBCharacteristic *characteristic in service.characteristics) {
if ([characteristic.UUID isEqual:[CBManager accelDataUUID]]) {
[peripheral setNotifyValue:YES forCharacteristic:characteristic];
} else if ([characteristic.UUID isEqual:[CBManager accelConfigUUID]]) {
[peripheral writeValue:[CBManager switchData:YES]
forCharacteristic:characteristic
type:CBCharacteristicWriteWithResponse];
}
//... if you have more to iterate
}
}

Answer 2

You need to check for the availability of the characteristic's notification.
From Apple's doc
When you subscribe to (or unsubscribe from) a characteristic’s value,
the peripheral calls the
peripheral:didUpdateNotificationStateForCharacteristic:error: method
of its delegate object. If the subscription request fails for any
reason, you can implement this delegate method to access the cause of
the error, as the following example shows:
-(void)peripheral:(CBPeripheral *)peripheral
didUpdateNotificationStateForCharacteristic:(CBCharacteristic *)characteristic
error:(NSError *)error {
if (error) {
NSLog(#"Error changing notification state: %#",
[error localizedDescription]);
}
...
Note: Not all characteristics offer subscription. You can determine
if a characteristic offers subscription by checking if its properties
attribute includes either of the CBCharacteristicPropertyNotify or
CBCharacteristicPropertyIndicate constants.