System.InvalidOperationException when drawing into HelixViewPort3D - process

Question

Always when I want to draw into ViewPort3D out from a process I get a System.InvalidOperationException.
What is it I do not understand?
Is a process not able to access the ui process?
How can I solve this problem?
private void Pro_OutputDataReceived(object sender, DataReceivedEventArgs e)
{
Random r = new Random();
DrawSphere(counter, Colors.Red, (double)r.Next(400) / 100);
counter++;
}
private void DrawSphere(int i, Color color, double radius)
{
SphereVisual3D sphere = new SphereVisual3D();
sphere.Center = new Point3D(i * 5, counter * 5, 0);
sphere.Visible = true;
sphere.Fill = new SolidColorBrush(color);
sphere.Radius = radius;
viewPort.Children.Add(sphere);
}

Answer 1

You need to use the dispatcher to check the access. You have 2 options:
First Option:
private void Pro_OutputDataReceived(object sender, DataReceivedEventArgs e)
{
Random r = new Random();
Application.Current.Dispatcher.Invoke(new Action(() => DrawSphere(counter, Colors.Red, (double)r.Next(400) / 100)));
counter++;
}
Second Option:
private void Pro_OutputDataReceived(object sender, DataReceivedEventArgs e)
{
Random r = new Random();
DrawToViewPort(counter, Colors.Red, (double)r.Next(400) / 100);
counter++;
}
private void DrawToViewPort(int i, Color color, double radius)
{
if (viewPort.Dispatcher.CheckAccess())
{
DrawSphere(i, color, radius);
}
else
{
viewPort.Dispatcher.Invoke((Action<int, Color, double>)DrawToViewPort, i, color, radius);
}
}