Trying to retrieve previously paired bluetooth dev

Sorry for the long title, but we are having a pretty interesting issue with using corebluetooth for ios. We are issuing a call to retrievePeripherals in CBCentralManager and are able to find the previously paired device.

This happens though regardless if the device is on or off though. I can't find anything in apple's documentation as to why it's able to find the device when it is off though and it isn't showing up in Settings -> Bluetooth -> Devices. I'm suspecting that Apple is caching this information but can't find any documentation to confirm this. Also, when the device is off and we issue the connect call, the program continues to execute as normal but the delegate for didFailToConnect never gets called. When the device is turned on, it will connect immediately.

Is there a way to pass a timeout parameter when trying to connect to a device? If not, what would the best solution be to handling reconnecting to a previously used device for an application (we're storing the last connected device within the app).

Two points you need to know about retrievePeripherals: and connectPeripheral:

1.) retrievePeripherals: attempts to retrieve the CBPeripheral object associated with the uuid you supply. Even if the ble device is off (or on the other side of the country) retrievePeripherals: will still return an instance of CBPeripheral that you can call connectPeripheral: on. This is done intentionally so that you can issue a call to a peripheral that is not even around and still automatically connect to it when it comes back into range. It basically creates a marker inside the system bluetooth so that when the device is actually seen, it will know it should connect to it.

2.)connectPeripheral: will not time out unless the communication channel is broken with the actual device. If the iOS device has not seen the device, it will not fail and should not time out (unless some error occurs inside the system bluetooth).

And as for the timeout parameter, there is no documented way inside the CoreBluetooth framework. You can create your own implementation for it, however I believe you'd be better off keeping a list of which peripheral uuid's you've actually called connectPeripheral: on and then just pop them from the list when they connect. If you no longer want to connect to a peripheral in the list call cancelPeripheral: on that UUID, call connectPeripheral: on the other, and swap entries. Good to go.