iOS CoreBluetooth operating as a peripheral and central simultaneously in the background

Question

I'm writing an app using CoreBluetooth in iOS8 that detects and connects to other phones using the app. I'm trying to figure out the best way to be able to create a connection while both apps are backgrounded, but have been having difficulty in the scenario where both phones are backgrounded + locked. I've followed the suggestions of this post:

How to detect nearby devices with Bluetooth LE in iOS 7.1 both in background and foreground?

I haven't been able to establish a connection when both phones are backgrounded + locked, but I've been able to get a connection where the peripheral and central are backgrounded + locked and I then unlock the central (central still in the background). When I unlock the peripheral though nothing happens. It also works when they are backgrounded but not locked.

So in order to allow a connection to be established when I unlock the "peripheral", I decided to create a central and peripheral on both phones to simultaneously scan and advertise. Whichever discovers the other first will then stop scanning/advertising and connect. I've run into problems with this method that are detailed in the following two questions:

Peripheral and central at the same time on iOS

iOS CoreBluetooth Simultaneous Peripheral and Central Managers

Basically, I think that when both of my devices try to connect to each other simultaneously, they get hung up on attempting to connect and didConnectPeripheral is never called on either of them (the last thing both of them displays is a message saying that they are attempting to connect). It has worked occasionally though so I'm also a little confused as to why there is a probabilistic nature to the connection. Does anyone have any suggestions on how to approach the problem? If there's a better way to establish a connection when both apps are backgrounded + locked, please let me know because that was my original problem.

Thanks!

Answer 1

Declare bluetooth-central and bluetooth-peripheral background modes in your Info.plist to act in both Central and Peripheral roles in background.