CoreBluetooth [WARNING]未知错误：2

Question

I'm developing a BLE app in iOS6. I got CoreBluetooth[WARNING] Unknown error: 2 when I call readValueForCharacteristic on a characteristic after it's set to notifying state.

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

The delegate callback gets called with an unknown error from NSLog: `Error updating value for characteristic Unknown (<fef2>) error: Error Domain=CBErrorDomain Code=0 "Unknown error." UserInfo=0x1dd3b7e0 {NSLocalizedDescription=Unknown error.}

Please give some advice.

Answer 1

From what I can tell, you cannot read the value of a characteristic that is set to notify.

You need to "subscribe" to notifications for that characteristic:

[peripheral setNotifyValue:YES forCharacteristic:characteristic];

The value can then be read in your delegate method:

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

The BLE docs for iOS are quite poor in this regard.