ScrollViewer Content size change then ScrollToOffset not working

I am using a scrollviewer to display an Image within it.

<ScrollViewer Name="scrollViewer1" Height="500" Width="500" HorizontalScrollBarVisibility="Auto" VerticalScrollBarVisibility="Auto" P开发者_如何学Cadding="0" >
    <Image x:Name="img1" Width="100" Source="/MyApp;component/Images/Test.jpg" />
</ScrollViewer>

But when I re-size the image in code, and immediately use the scrollViewer.ScrollToHorizontalOffset() (to reposition the image) it does not work :

img1.Width = 1000;
scrollViewer1.ScrollToHorizontalOffset(500);

I verified the ScrollableWidth property after the img1.Width = 1000 indeed it is not updated yet. So I used the UpdateLayout() right after I resize the image, great now the ScrollableWidth is updated :

img1.Width = 1000;
scrollViewer1.UpdateLayout();
scrollViewer1.ScrollToHorizontalOffset(500);

but the ScrollToHorizontalOffset is still not working. If I do it afterwards, on another user button click it works though. :/

Anyone has a clue?

---

Nevermind... My error, the example above works. In my project I was basing the ScrollToHorizontalOffset on the img1.ActualWidth which was not updated.

Sorry :/