mLeScanCallback.kt

 private fun scanLeDevice(enable: Boolean) {
        when (enable) {
            true -> {
                // Stops scanning after a pre-defined scan period.
                Handler().postDelayed({
                    mScanning = false
                    bluetoothAdapter?.bluetoothLeScanner?.stopScan(mLeScanCallback)
                }, 5000)
                mScanning = true
                bluetoothAdapter?.bluetoothLeScanner?.startScan(mLeScanCallback)
            }
            else -> {
                mScanning = false
                bluetoothAdapter?.bluetoothLeScanner?.stopScan(mLeScanCallback)
            }
        }

    }

 private var mLeScanCallback: ScanCallback =
            object : ScanCallback() {
                override fun onScanResult(callbackType: Int, result: ScanResult?) {
                    super.onScanResult(callbackType, result)
                    //Do your thing
                }

                override fun onBatchScanResults(results: List<ScanResult?>?) {
                    super.onBatchScanResults(results)
                    //Do your thing
                }

                override fun onScanFailed(errorCode: Int) {
                    super.onScanFailed(errorCode)
                    //Do your thing
                }
            }