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I have a BluetoothDevice with it's associated BluetoothGatt object. This is a device that the user connects to daily, and it does not have any characteristics or services that change often.

Right now in order to interact with the device, after each connect I have to first discover all services, which often adds 1-5 seconds of delay to the whole process.

My question is: is it possible to save a cache of my devices' services and characteristics so that I don't have to actually do a call to discoverServices after each connect ?

zrgiu
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  • You can have a try .Cache all uuid at first. Then don't discoverServices .And use function like getService(UUID). – tiny sunlight Dec 20 '15 at 08:02
  • getService(UUID) requires the services to be loaded first, and it only looks it up in the local (very temporary) internal cache. – zrgiu Dec 20 '15 at 18:08

2 Answers2

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I don't know about iOS phones but Android phones always cach the discovered characteristics and services so that service discovery takes shorter time compared to first connection. See this thread .

You question should be whether it is possible to eliminate service discovery or not at all. According to Bluetooth spec, you don't need to perform service discovery after each connection. If you know the UUIDs of the characteristic and its service, it is possible to directly do (without service discovery) GATT operations based on the characteristic properties.

Android requires service discovery to instantiate BluetoothGattService and BluetoothGattCharacteristic objects. However, you can instantiate your own BluetoothGattService and BluetoothGattCharacteristic objects by looking into the source code of Android and using Java reflections. You can first create these objects with the constructors which are available in BLE API. Then to hook the characteristics to services, and services to BluetoothGatt object, you will need to use Java reflection methods. To do that, you should read the source code of the classes (just hold control and click on the class in Android Studio to view the source code). I, by myself implemented this and soon I will update this thread with my blog post, but here is a sneak peek:

BluetoothGattService mService = new BluetoothGattService(mServiceUuid, BluetoothGattService.SERVICE_TYPE_PRIMARY);
    BluetoothGattCharacteristic mCharacteristic1 = new BluetoothGattCharacteristic(mChar1Uuid, BluetoothGattCharacteristic.PROPERTY_WRITE, 0);
    BluetoothGattCharacteristic mCharacteristic2 = new BluetoothGattCharacteristic(mChar2Uuid, BluetoothGattCharacteristic.PROPERTY_NOTIFY, 0);
    BluetoothGattDescriptor mChar2Cccd = new BluetoothGattDescriptor(mCccdUuid, 0);

You should use Java reflection methods; firstly to hook the characteristics to the service; secondly service to BluetoothGatt instance which is instantiated as soon as the BLE Gatt connection is established.

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ulusoyca
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  • Looking forward to seeing your blog post! I already tried creating all the services and characteristics programmatically, but that didn't work for me. All the write calls were ignored. As for the Android-internal caching - that's not a permanent cache. It actually gets erased quite often. I want it to not be erased at all, or maybe once a year. – zrgiu Dec 20 '15 at 17:10
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    any news with that blog post ? – zrgiu Jan 29 '16 at 19:16
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    Don't do this. OEMs are free to modify AOSP source to their liking. Your reflection might work on the few phones you have available for testing. But this will give you headaches as BT starts failing for your users out in the wild. There is a reason that internal stuff is hidden from you. – tir38 Oct 16 '17 at 21:10
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    That is totally true. Those were the days I was less experienced in coding @tir38 – ulusoyca Oct 19 '17 at 10:58
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For iOS, it won't work. If you don't call discoverServices for each connect,your Peripheral instance's services property will always be nil,so is services' characters. Anything after that won't work.

If you have yet to call the discoverServices: method to discover the services of the peripheral, or if there was an error in doing so, the value of this property is nil.

wj2061
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