Android 4.3 Bluetooth Low Energy Unstable

Android 4.3 Bluetooth Low Energy unstable

Important implementation hints

(Perhaps some of those hints aren't necessary anymore due to Android OS updates.)

1. Some devices like Nexus 4 with Android 4.3 take 45+ seconds to connect using an existing gatt instance. Work around: Always close gatt instances on disconnect and create a fresh instance of gatt on each connect.
2. Don't forget to call android.bluetooth.BluetoothGatt#close()
3. Start a new thread inside onLeScan(..) and then connect. Reason: BluetoothDevice#connectGatt(Context context, boolean autoConnect, BluetoothGattCallback callback) always fails, if called inside LeScanCallback() {...}.onLeScan(BluetoothDevice device, int rssi, byte[] scanRecord) in the same thread on Samsung Galaxy S3 with Android 4.3 (at least for build JSS15J.I9300XXUGMK6)
4. Most devices filter advertising
5. Better not use android.bluetooth.BluetoothAdapter#startLeScan(UUID[] serviceUuids, LeScanCallback callback) with the parameter to filter for certain service UUIDs because this is broken completely in Samsung Galaxy S3 with Android 4.3 and doesn't work for 128bit UUIDs in general.
6. Gatt always can process one command at a time. If several commands get called short after another, the first one gets cancelled due to the synchronous nature of the gatt implementation.
7. I often see even on modern devices with Android 5, that Wifi interferes withs bluetooth and vice versa. As a last resort, turn off wifi to stabilize bluetooth.

Tutorial for beginners

A pretty OK entry point for newcomers could be this video tutorial: Developing Bluetooth Smart Applications for Android http://youtu.be/x1y4tEHDwk0

The issue and work around described below is probably fixed now by OS updates

Work around: I could "stabilize" my app doing that...

1. I provide the user a setting "Restart Bluetooth". If that setting is enabled, I restart Bluetooth at some points that indicate the begin of BLE stack becoming unstable. E.g. if startScan returns false. A good point may also be if serviceDiscovery failes. I just turn Bluetooth off and on.
2. I provide another setting "Turn off WiFi". If that setting is enabled, my app turns off Wifi when the app is running (and turns it back on afterwards)

This work around is based on follwoing experiences...

• Restarting Bluetooth helps to fix problems with BLE in most cases
• If you turn off Wifi, the BLE stack gets much more stable. However, it also works fine on most devices with wifi turned on.
• If you turn off Wifi, restarting Bluetooth fully recovers the BLE stack without the need to reboot the device in most cases.

Bluetooth Low Energy (BLE) implementation below 4.3 (API 18)

This is possible on specific devices, with very heavy fragmentation.

See:

• https://github.com/cjhuo/Android-Samsung-Ble-APIs-Bluez for Samsung devices with Android 4.1 e.g. some Galaxy S3 with original OS version.
• http://developer.samsung.com/ble for Samsung devices with Android 4.2 (e.g. Galaxy S4 with original OS version)
• https://www.htcdev.com/devcenter/opensense-sdk/bluetooth-smart/htc-ble-installation/ for HTC devices with Android 4.x

There may be more for other vendors...

I would advise sticking with Android 4.3 as much as possible, using the specific SDKs below 4.3 is a mess.

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