Question

I am using C#, Silverlight, Visual Studio for Windows Phone 7.

I am looking for an event that fires when a scroll has finished scrolling. I am interested in getting the final positions of certain elements.

LayoutUpdated gets fired a few times during a scroll, but not consistently at the end of the scrolling. ManipulationCompleted some times works, but if the user does a “flick” motion on the scroll, ManipulationCompleted fires before the scroll stops moving.

Please note that I am working in Silverlight and scroll events like ScrollChanged just simply do not exist.

Thanks in advance.

Answer 1

I solved this problem by tapping into the VisualStateGroup of the ScrollViewer.

// uie is a UIElement
IEnumerable<ScrollViewer> svList = uie.GetVisualDescendants<ScrollViewer>();
if (svList.Count() > 0)
{
    // Visual States are always on the first child of the control
    FrameworkElement element = VisualTreeHelper.GetChild(svList.First<ScrollViewer>(), 0) as FrameworkElement;
    // getting all the visual state groups
    IList groups = VisualStateManager.GetVisualStateGroups(element);
    foreach (VisualStateGroup group in groups)
    {
        if (group.Name == "ScrollStates")
        {
            group.CurrentStateChanged += new EventHandler<VisualStateChangedEventArgs>(group_CurrentStateChanged);
        }
    }
}

private static void group_CurrentStateChanged(object sender, VisualStateChangedEventArgs e)
{
    if (e.NewState.Name == "NotScrolling")
    {
        isNotScrolling = true;
    }
    else
    {
        isNotScrolling = false;
    }
}

The only problem I have encountered with this is that the ScrollStates’s state changes very slowly, so other events that the app fires will process before your code even registers a scroll.