Silverlight 4 web cam permission on load of User Control

I am using Silverlight 4 to access the web cam. Everything works ok when I start the web cam on a button click event, I get the prompt for permission. I would like the web cam to start when User Control loads, but for some reason when I run the same code on the Loaded event, I don't get a prompt when executing the following code:'

Ca开发者_运维问答ptureDeviceConfiguration.RequestDeviceAccess()

Does anyone have a work around for this?

I found a workaround to the problem. I am automatically clicking the button that starts the webcam streaming on the Loaded event of the control.

ButtonAutomationPeer peer = new ButtonAutomationPeer(btnStartWebcam);
IInvokeProvider invokeProv = 
    peer.GetPattern(PatternInterface.Invoke) 
    as IInvokeProvider;
invokeProv.Invoke();

This does the job for me because I don't mind having a button on the UI. But I guess you can create a dummy one and hide it if it's necessary.

The security around accessing local devices is very tight. Starting the capture must be preceded by a user action.

Instead of starting the capture from the loaded event, you'll have to move it to a Click event.

Code behind:

public void StartCam()
{
  VideoCaptureDevice dev = CaptureDeviceConfiguration.GetDefaultVideoCaptureDevice();
  if(CaptureDeviceConfiguration.RequestDeviceAccess() &&
     CaptureDeviceConfiguration.AllowedDeviceAccess)
  {
    CaptureSource capture = new CaptureSource();
    capture.VideoCaptureDevice = dev;

    VideoBrush videoBrush = new VideoBrush();
    videoBrush.SetSource(capture);

    capture.Start();

    WebCamRectangle.Fill = videoBrush;
  }
}

private void button1_Click(object sender, RoutedEventArgs e)
{
  StartCam();
}

Xaml:

<Grid x:Name="LayoutRoot" Background="White">
    <Grid.RowDefinitions>
        <RowDefinition Height="49*" />
        <RowDefinition Height="251*" />
    </Grid.RowDefinitions>
    <Rectangle Name="WebCamRectangle" 
               Stroke="Black" StrokeThickness="1" Grid.Row="1" />
    <Button Content="Start" Height="25" HorizontalAlignment="Left" 
            Margin="12,12,0,0" Name="button1" VerticalAlignment="Top"
            Width="135" Click="button1_Click" />
</Grid>