central unsubscribes from characteristic when restart app

Question

IOS app is a peripheral. After pairing, peripheral can successfully update characteristic value to and indicate to subscribed central via updateValue:forCharacteristic:onSubscribedCentrals:

When I call this method successfully (after pairing), logs show that characteristic had 1 subscribed central, via characteristic.subscribedCentrals.

However, If I use Xcode to stop and start the app again and try to update characteristic value, logs show that characteristic now has 0 subscribed centrals, and central device doesnt do expected behavior so I'm assuming it wasnt received.

How I make sure the central remains subscribed to my services characteristic after reboot/reconnect?

Thanks

Answer 1

I believe that the only way you can do this is to create a bond between the devices. Usually, once the app is killed/restarted, the value of the CCCD (Client Characteristic Configuration Descriptor) is reset and therefore the remote central app needs to re-enable it every time upon connection. However, when the two devices bond, the GATT server stores the information on which CCCDs are enabled, and then upon each subsequent connection those CCCD values are loaded. You can find more information here:-

• What does CCCD mean
• How to know if the notification/indication of a characteristic is enabled
• GATT (Services and Characteristics) - check attribute caching
• The ultimate guide to iOS's CoreBluetooth - check Pairing and Bonding