Element is already a child of another element in PrintDocument

[Roger]

I have created a UIElement in which my layout for "Reports - Receipt - Print".
The layout contains  Binding and other controls.

When I Click the Button for print
It throws an exception "Element is already the child of another element.".
In this line ----> canvas.Children.Add(this.DRReceipt);

<StackPanel x:Name="DRReceipt">

...RadGriView with binding...
...Label...
...Images...

</StackPanel>

var doc = new PrintDocument();

var offsetY = 0d;
var totalHeight = 0d;

Canvas canvas = new Canvas();
canvas.Children.Add(this.DRReceipt);

doc.PrintPage += (s, d) =>
{
    d.PageVisual = canvas;
    if (totalHeight == 0)
    {
        totalHeight = canvas.DesiredSize.Height;
    }
    Canvas.SetTop(canvas, -offsetY);
    offsetY += d.PrintableArea.Height;
    d.HasMorePages = offsetY <= totalHeight;
};
doc.Print("DeliveryReceipt");