DeviceInformation.FindAllAsync() doing nothing

问题

I've been using a camera BarcodeScanner (Microsoft's BarcodeScanner API) for 3 weeks now in my UWP application. It's working well but sometimes, the preview window of the barcode is not opening and the BarcodeScanner is not turning on.

When I figured this out, I took my app in debug mode to see where was the problem and if they were some exceptions thrown.

Here's how I'm initializing the BarcodeScanner :

public async Task ClaimScannerAsync()
{
    string selector = Windows.Devices.PointOfService.BarcodeScanner.GetDeviceSelector();
    DeviceInformationCollection deviceCollection = await DeviceInformation.FindAllAsync(selector);

    if (_scanner == null)
        _scanner = await Windows.Devices.PointOfService.BarcodeScanner.FromIdAsync(deviceCollection[0].Id);

    if (_scanner != null)
    {
        if (_claimedBarcodeScanner == null)
            _claimedBarcodeScanner = await _scanner.ClaimScannerAsync();

        if (_claimedBarcodeScanner != null)
        {
            _claimedBarcodeScanner.DataReceived += ClaimedBarcodeScanner_DataReceivedAsync;
            _claimedBarcodeScanner.ReleaseDeviceRequested += ClaimedBarcodeScanner_ReleaseDeviceRequested;
            _claimedBarcodeScanner.IsDecodeDataEnabled = true;
            _claimedBarcodeScanner.IsDisabledOnDataReceived = true;
            await _claimedBarcodeScanner.EnableAsync();
            //await _claimedBarcodeScanner.ShowVideoPreviewAsync();
            await _claimedBarcodeScanner.StartSoftwareTriggerAsync();
            await StartPreviewAsync();

            Debug.WriteLine("Barcode Scanner claimed");
        }
    }
}

... and the problem seems to come from the line :

DeviceInformationCollection deviceCollection = await DeviceInformation.FindAllAsync(selector);

Called in :

internal async Task OnBarcodeExecuted(object dataContext)
{
    try
    {
        CurrentDataContext = dataContext;
        _scanner.Subscribe(OnBarcodeReceived);
        await _scanner.ClaimScannerAsync();
    }
    catch(Exception e)
    {
        Debug.WriteLine(e.Message);
    }

}

OnBarcodeReceived in my ViewModel :

private void OnBarcodeReceived(string barcode)
{
    var ignored = Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
    {
        if(CurrentDataContext is IScannable)
        {
            IScannable item = (IScannable)CurrentDataContext;
            item.NumSerie = barcode;
        }
    });

}

where the code is just stopping and waiting without throwing an error.

So if someone could explain to me, why it's doing that and why the code doesn't throw any error after a certain amount of time ?

来源：https://stackoverflow.com/questions/56649293/deviceinformation-findallasync-doing-nothing

标签

uwp

barcode-scanner