WPF TranslateTransform Error - wpf

Question

I have a StackPanel that I am sliding left and right to simulate moving pages using TranslateTransform.
If I call the slide method once it works well. If I call my slide method twice in quick succession (in code), the second transform has the wrong start position and ends up in the wrong place.
How do I get my second translate to "refresh" its starting position?
Here is the StackPanel
<StackPanel
x:Name="MainPanel"
Orientation="Horizontal">
<StackPanel.RenderTransform>
<TranslateTransform
x:Name="MainPanelTransform"
/>
</StackPanel.RenderTransform>
</StackPanel>
Here is the slide code:
private void SlidePage(int pagesToMove)
{
Storyboard sb = SlideEffect(MainPanel, (-PageWidth * pagesToMove));
sb.Completed += SlideCompleted;
sb.Begin();
}
private Storyboard SlideEffect(UIElement controlToAnimate, double positionToMove)
{
//Get position of stackpanel
var gt = controlToAnimate.TransformToVisual(MainGrid);
var p = gt.Transform(new Point(0, 0));
//add new storyboard and animation
var sb = new Storyboard();
var da = new DoubleAnimation { To = p.X + positionToMove };
Storyboard.SetTarget(da, controlToAnimate);
Storyboard.SetTargetProperty(da, new PropertyPath("RenderTransform.(TranslateTransform.X)"));
//Storyboard.SetTargetProperty(da, new PropertyPath("RenderTransform.Children[0].X"));
var ee = new ExponentialEase { Exponent = 6.0, EasingMode = EasingMode.EaseOut };
da.EasingFunction = ee;
sb.Children.Add(da);
return sb;
}
The offending line of code is this:
var p = gt.Transform(new Point(0, 0));
The second time I call the SlideEffect method it has the same value as the first time. It seems like the animations are getting buffered and run together. Is there any way to stop the buffering?

Answer 1

Did you try to change a FillBehavior property of Storyboard?
UPDATE:
I have a bug in VS, so I couldn't reproduce your situation. But I may recommend you:
Try to disable the EasingFunction. Maybe Storyboard.Completed fires before the Storyboard actually completed;
Are you sure, that transform changes actual coordinates? I think it is the solution, but not sure.
In the Storyboard.Completed you could manually update transform coordinates:
MainPanelTransform.BeginAnimation(TranslateTransform.XProperty, null);
MainPanelTransform.X = -100;