Silverlight 4 - Render UIElement as an Image

Question

I have a UIElement that I want to capture a snapshot of when a user clicks a button. When a user clicks the button, I want to take the UIElement and load it's current state into an Image element. How do I render a UIElement as an Image?

Answer 1

Assuming the FrameworkElement you want to render is named elementToRender and the Image where you want to place the rendered output is called image, use the following code on your button's click handler:

var writeableBitmap = new WriteableBitmap((int)elementToRender.RenderSize.Width, (int)elementToRender.RenderSize.Height);

writeableBitmap.Render(elementToRender, new ScaleTransform() { ScaleX = 1, ScaleY = 1 });
writeableBitmap.Invalidate();

image.Source = writeableBitmap;

Answer 2

You can also do the following:

private void SetImageSourceBasedOnElement(Image image, UIElement element)
{
    if (element != null)
    {
        WriteableBitmap writableBitmap = new WriteableBitmap(element, null);
        writableBitmap.Invalidate();

        image.Source = writableBitmap;
     }
 }

Answer 3

WriteableBitmap wb = new WriteableBitmap(UIElement, new ScaleTransform() { ScaleX = 1, ScaleY = 1 });
wb.Invalidate();
Image.Source = wb;

Answer 4

Ultimately, no, you cannot render an entire UIElement, including the parts that aren't visible due to scrolling overflow, etc.

I looked into how you could get around this using reflection. Unfortunately, you cannot override how UIElement renders, as it is just a light wrapper for the internal class XcpImports, which in turn is a wrapper for various native methods used throughout Silverlight. In other words, UIElement and how it is rendered is completely native, and thus there is no (easy) way to override how it displays using reflection.

If you wanted to take the hackish approach, you could enclose your element in a Grid, remove it from that grid, put it in another grid that is the same size as the element--see where I'm going with this? But that would be quite a hassle, and hackish at best.