Wsrtjtyk

I'm trying to get a simple test working to learn how to setup and use multiple USB video devices at once in a Universal Windows project (later to be used on a raspberry Pi running windows 10 IoT core). I want the UI to display a preview of the selected camera. I have successfully followed the preview example on the MediaCapture site HERE

I have a 'TakePicture' class that will later be used for other things, but is currently used to find and initialize the video devices attached to the system as follows

public static class TakePicture

{

private static List<CaptureElement> _captureElements;

private static List<MediaCapture> _mediaCaptures;

public static DeviceInformationCollection devices;

private static int currentDevice = 0;



public static async Task InitializeDevice()

{

    if (currentDevice >= _captureElements.Count)

    {

        _mediaCaptures.Add(new MediaCapture());

        var captureElement = new CaptureElement{Stretch = Stretch.UniformToFill};

        _captureElements.Add(captureElement);

        await _mediaCaptures[currentDevice].InitializeAsync(

            new MediaCaptureInitializationSettings

            {

                VideoDeviceId = devices[currentDevice].Id,

                StreamingCaptureMode = StreamingCaptureMode.Video



            });

        _captureElements[currentDevice].Source = _mediaCaptures[currentDevice];

    }

}



public static void IncrimentDevice()

{



    currentDevice = (currentDevice + 1) % devices.Count;

}







public static async Task<MediaCapture> getPreviewElement()

{

    CaptureElement element = new CaptureElement();

    await FindDevices();

    await InitializeDevice();

    return _mediaCaptures[currentDevice];



}





public static async Task FindDevices()

{

    if (devices == null)

    {

        devices = await DeviceInformation.FindAllAsync(DeviceClass.VideoCapture);

        _captureElements = new List<CaptureElement>();

        _mediaCaptures = new List<MediaCapture>();

    }

}





}

I want to return a MedaCapture object related to a camera and use that to set the source of the CaptureElement in the GUI as follows:

private async Task StartPreviewAsync()

    {

        MediaCapture capture = await TakePicture.getPreviewElement();

        await capture.StartPreviewAsync();

        PreviewImage.Source = capture;

        PreviewImage.Visibility = Visibility.Visible;

    }

the 'PreviewImage' is a reference to a capture element in the UI:

<CaptureElement Name="PreviewImage" Stretch="Uniform" HorizontalAlignment="Center" Height="649" Margin="0,84,0,0" VerticalAlignment="Top" Width="1147"/>

BUT every time I try and set the source to the MediaCapture element I get a null reference exception. I have checked in the debugger that this object is not null and has the ID of a connected device, further to this when I run

await capture.StartPreviewAsync(); 

the green light below the camera lights up on the camera. If i try to re-initialize the MediaCapture object returned by GetPreviewElement it throws an exception that the device is already initialized too.

Am i approaching setting up multiple devices correctly? is passing a copy of the initialized MediaCapture a valid way of setting the source of the CaptureElement?

Many thanks!