Automatically connecting to a previous Bluetooth device through Objective C

Question

My program allows users to connect to a bluetooth device and it'll save the UUID. The next time the application launches, it automatically connects to a previously connected device.

I'm saving the UUIDs in[NSUserDefaults standardUserDefaults] in an NSArray.

I'm able to retrieve the first device and connect to it, by using the retrievePeripherals method for CBCentralManager, and passing in an array of UUIDs that I stored.

My problem is, I don't know how to handle for errors. I want the program to know if it failed to connect to the first UUID and go onto the next one. The delegate method didRetrievePeripherals seems to retrieve the device with the specific UUID, even though I turned the device OFF.

Did anyone else have the same problem?

Answer 1

retrievePeripherals: uses the core bluetooth internal database to return a CBPeripheral. Once you connected to a peripheral, it will be persisted in the database and you can retrieve it. It is not not checked whether the peripheral is turned on or not.

Unfortunately, there is no way to determine for what reason a device is not available but you can create your own heuristics:

• try to connect for a specific time and if you don't receive the didConnectPeripheral: callback in a reasonable time (usually a few seconds), then that peripheral is considered off range and you can go on with the next peripheral. Note that the connectPeripheral will keep on running (even in the background) as long as it does not succeed or not cancelled/terminated.
• if the peripheral is advertising, then you can try to run a scan too to check whether it is in range.