onServicesDiscovered never called while connecting to GATT Server

Question

I have a bluetooth headset which is paired with my Nexus 5X (running Android 7.1) and I would like to connect to a GATT Server of the headset. I tried it with the following

Answer 1

This may help

I will explain in two steps: connecting and discovering services

connecting: connect from mainthread

set auto-reconnect to false

if version greater than or equals to M, set Transport type

else directly use reflection and handle it properly

Handler(applicationContext.mainLooper).post {
                    Log.d(TAG, " Post is called inside mainlooper")
                    mBluetoothGatt = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
                        Log.d(TAG, " Is Or Greater than M $mBluetoothDevice")
                        mBluetoothDevice!!.connectGatt(this, false,
                                onGhattListener, TRANSPORT_LE)
                    } else {
                        Log.d(TAG, " Less than M")
                        try {
                            Log.d(TAG, " Trying TRANPORT LE with reflection")
                            val m = mBluetoothDevice!!.javaClass.getDeclaredMethod("connectGatt", Context::class.java, Boolean::class.javaPrimitiveType, BluetoothGattCallback::class.java, Int::class.javaPrimitiveType)
                            m.isAccessible = true
                            val transport = mBluetoothDevice!!.javaClass.getDeclaredField("TRANSPORT_LE").getInt(null)
                            m.invoke(mBluetoothDevice, this, false, onGhattListener, transport) as BluetoothGatt
                        } catch (e: Exception) {
                            e.printStackTrace()
                            Log.d(TAG, " Catch to call normal connection")
                            mBluetoothDevice!!.connectGatt(this, false,
                                    onGhattListener)
                        }
                    }
                    Log.d(TAG, "mBluetooth gatt is $mBluetoothGatt")
                    mBluetoothGatt?.let {
                        refreshDeviceCache(mBluetoothGatt!!)
                    }
                }

discover services : in onGhattListener , if device is connected fire discoverServices() from main thread

override fun onConnectionStateChange(gatt: BluetoothGatt, status: Int,
                                         newState: Int) {
        Log.d(TAG, "onConnectionStateChange $gatt and status $status and newstate $newState")
        when (newState) {
            BluetoothGatt.STATE_CONNECTED -> {
                Handler(Looper.getMainLooper()).post {
                    gatt.discoverServices()
                }
            }
            BluetoothGatt.STATE_DISCONNECTED -> {

            }
            BluetoothGatt.STATE_CONNECTING -> {

            }
            BluetoothGatt.STATE_DISCONNECTING -> {

            }
        }
    }

this may solve your problem

call refresh method with reflection

fun refreshDeviceCache(gatt: BluetoothGatt): Boolean {
    try {
        val localMethod = gatt.javaClass.getMethod("refresh")
        if (localMethod != null) {
            return localMethod.invoke(gatt) as Boolean
        }
    } catch (localException: Exception) {
        Log.e(TAG, "An exception occured while refreshing device")
        localException.printStackTrace()
    }
    return false
}