Apple

So I guess I need to think about how we allocate characteristics to services and probably keep them to a minimum, optimise for battery life of my peripheral. Otherwise there is going to be lots of wasted data in the form or custom characteristic UUID’s (128 bit) whenever I discover characteristics on each connection, simply to re-instantiate my service & characteristic objects.

From: Jason Conn [mailto:email@hidden]
Sent: 03 June 2013 16:58
To: email@hidden
Cc: 'András Kövi'; 'Rick Mann'; 'email@hidden Bluetooth'

Subject: Re: Can I keep CBService and CBCharacteristics around?

As of iOS 6.0, services and characteristics are cached by the system whenever possible.

There is no need to keep them around between connections - it isn't explicitly supported, and you may be opening yourself to non-obvious issues like them being invalidated underneath you if the remote database changes.

On Jun 3, 2013, at 6:01 AM, Steve Childerley <email@hidden> wrote:

Hi Andras,

I would prefer not to have to perform this kind of thing, as I don’t need the security I just want to side effect of CBService and CBCharacteristics persisting between connections. It wouldn’t be necessary if they weren’t dealloc’d on disconnect. The alternative being to rediscover each time – costly and time consuming but probably the route I will take in the short term.

Perhaps persisting, between connections, (not between instances of CBCentralManager) is functionality that might be added in a future release?

Thanks, Steve.

From: András Kövi [mailto:allprog@gmail.com]
Sent: 03 June 2013 13:33
To: email@hidden
Cc: Etan Kissling; Rick Mann; email@hidden Bluetooth
Subject: Re: Can I keep CBService and CBCharacteristics around?

Hi Steve,

encryption requires paired devices. Pairing is done with the dialog you mention and your app has no way to dismiss it programmatically. Theoretically it has to be done only once.

I am, of course, not aware of all your requirements but I'd suggest you to try to avoid this kind of caching. Leave it up to the system to do it for you unless you have some performance issue that may be solved in this way.

Side note: I feel like this is similar to when you want to cache images but use [UIImage imageNamed:] to obtain them. It may seem to make sense but at the same time UIImage aready does it for you, so it practically just makes things more complex without much gain. I haven't done testing as to how much caching CoreBluetooth does but I feel like this is something that is necessarily an OS function. On the other hand, people on this list have been complaining that it does actually cache quite aggressively, which hinders testing in some cases. All in all, implementing additional caching will surely make your code more complex (think of handling BT reset, crashes, hidden XPC errors, etc.) without much practical gain (if any).

Regards,

Andras

2013/6/3 Steve Childerley <email@hidden>

Hi Etan,

I am trying to implement your recommendation to Rick earlier in the year.

The aim being simply to "keep CBService and CBCharacteristics around"
between connections.

I have, I believe, set my peripheral (BLE112 from BlueGiga) for encryption
only behaviour, however during the GATT interaction phase of my connection,
the iDevice requests permission to pair with the remote peripheral (via a
dialogue box).

This is something that I believe is not necessary if I simply wish to have
an encrypted link? If response to this dialogue is necessary to proceed, is
there anyway my App and respond to the dialogue - as I don't wish the use to
be aware of it?

Thanks, Steve.

-----Original Message-----
From: bluetooth-dev-bounces+steve=email@hidden
[mailto:bluetooth-dev-bounces+steve=email@hidden] On Behalf
Of Etan Kissling
Sent: 12 March 2013 10:24
To: Rick Mann
Cc: email@hidden Bluetooth
Subject: Re: Can I keep CBService and CBCharacteristics around?

Rick,

services and characteristics have to be re-discovered after every connect if
the link is not encrypted.

If encryption is active, you may find cached services / characteristics in
the peripheral's services and
their characteristics. Not sure about it, as I did not test that.

The peripheral object itself can only be reused if you still have the same
CBCentralManager instance.
If you create a new one, you can pass the UUID to retrievePeripherals in
order to get a new CBPeripheral
instance. Note that this does only work for devices that were previously
connected and, therefore, have
a UUID.

Etan

On 12.03.2013, at 07:49, Rick Mann <email@hidden> wrote:

> If I've scanned for my peripherals, connected, enumerated the services and
characteristics, can I keep those objects around for later reads? What
happens if the peripheral disconnects and reconnects?
>
> --
> Rick
>
>
>
>
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