private async void ScannerSelection_Changed(object sender, SelectionChangedEventArgs args)
    {
        var selectedScannerInfo = (BarcodeScannerInfo)args.AddedItems[0];
        var deviceId = selectedScannerInfo.DeviceId;

        if (isSelectionChanging)
        {
            pendingSelectionDeviceId = deviceId;
            return;
        }

        do
        {
            await SelectScannerAsync(deviceId); <- ошибка тут

            // Stop takes precedence over updating the selection.
            if (isStopPending)
            {
                await CloseScannerResourcesAsync();
                break;
            }

            deviceId = pendingSelectionDeviceId;
            pendingSelectionDeviceId = null;
        } while (!String.IsNullOrEmpty(deviceId));
    }

private async Task SelectScannerAsync(string scannerDeviceId)
    {
        isSelectionChanging = true;

        await CloseScannerResourcesAsync();

        selectedScanner = await BarcodeScanner.FromIdAsync(scannerDeviceId);

        if (selectedScanner != null)
        {
            claimedScanner = await selectedScanner.ClaimScannerAsync();
            if (claimedScanner != null)
            {
                await claimedScanner.EnableAsync();
                claimedScanner.Closed += ClaimedScanner_Closed;
                ScannerSupportsPreview = !String.IsNullOrEmpty(selectedScanner.VideoDeviceId);
                RaisePropertyChanged(nameof(ScannerSupportsPreview));

                claimedScanner.DataReceived += ClaimedScanner_DataReceived;

                if (ScannerSupportsPreview)
                {
                    await StartMediaCaptureAsync(selectedScanner.VideoDeviceId);
                }
            }
            else
            {
                //rootPage.NotifyUser("Failed to claim the selected barcode scanner", NotifyType.ErrorMessage);
            }

        }
        else
        {
            //rootPage.NotifyUser("Failed to create a barcode scanner object", NotifyType.ErrorMessage);
        }

        IsScannerClaimed = claimedScanner != null;
        RaisePropertyChanged(nameof(IsScannerClaimed));

        isSelectionChanging = false;
    }