Totally Disconnect a Bluetooth Low Energy Device

user_804440 0
Viewed 23360

I connect to a BLE device with the connectGatt() method in Android. This works great.

When I disconnect I use the following:

private void disconnectDevice() {
    gatt.disconnect();
}

When I receive the callback I do a close.

private BluetoothGattCallback gattCallback = new BluetoothGattCallback() {
    @Override
    public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
        switch (newState) {
            case BluetoothProfile.STATE_CONNECTED:
                Log.d("BLED-GATT", "STATE_CONNECTED");
                setUIConnectionStatus("Discover services on device...", Color.YELLOW);
                checkEnableAddButton(simpleTrackEditText.getText().toString());
                gatt.discoverServices();
                break;
            case BluetoothProfile.STATE_DISCONNECTED:
                Log.d("BLED-GATT", "STATE_DISCONNECTED");
                setUIConnectionStatus("Not Connected!", Color.RED);
                gatt.close();
                break;
            default:
                Log.d("BLED-GATT", "STATE_OTHER");
        }
    }
}

This is executed and I can no longer control the device after calling disconnectDevice(). The device itself seems to think that it is still connected since I cant put it in broadcasting visibility mode (which happens if it already has a connection). However, if I kill the application and open it again then I can set the device in broadcasting mode. This tells me the app was not properly disconnected.

Any idea what I missed here?

iot bluetooth-lowenergy bluetooth android
4 Answers

I experienced same problem and I found two possible root cause as follows: 1. Was same as @nilsi answer, connect to the same device more than once in one scanning. ā†’ solved by lock & List 2. connect to the device in one scanning and didn't get onConnectionStateChange, than I scanned again, it resulted in second connection to the same device. ā†’ solved by keeping BluetoothGatt object when I call device.connectGatt(), and call object.disconnect(), object.close() before scanning.

My test phone is 4 years old so sometimes it needs more than 20 seconds to return onConnectionStateChange....

user_37255010

As previously stated, the problem is caused by calling connectGatt multiple times. Each one of those calls create a new BluetoothGatt instance and they are all kept alive, while you have only the last one. Given the fact that sometimes it is needed to call connectGatt multiple times, I just keep all the instances that it returns and call disconnect/close on all of them when I'm done. This fixed the disconnection issue instantly

private val gattInstances = LinkedList<BluetoothGatt>()


fun connect() {
    bluetoothGatt = device?.connectGatt(
        context,
        false, gattCallback, TRANSPORT_LE
    )
    bluetoothGatt?.let { gattInstances.add(it) }
}

fun finish() {
    bluetoothGatt?.close()
    while (gattInstances.isNotEmpty()) {
        gattInstances.pop().apply {
            disconnect()
            close()
        }
    }
}
user_22967980
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