Currently there is no direct provision to attain this in WP7. I’ll walk through the code which will help you to identify if a list is scrolling or not. Later at the end there ia a full working sample attached.
My sample is straight forward. I’ll be changing the page title to “Scrolling” when we scroll the list and “NotScrolling” while it is stationary.
We have a list called theList.
1. Now attach a Loaded event to the page constructor:
public MainPage()
{
InitializeComponent();
Loaded += new RoutedEventHandler(MainPage_Loaded);
theList.ItemsSource = GetListData(60);
}
2. Define a variable to identify if ScrollEvent has been hooked already:
bool alreadyHookedScrollEvents = false;
3. Define MainPage_Loaded handler. All major work will be done here:
void MainPage_Loaded(object sender, RoutedEventArgs e)
{
if (alreadyHookedScrollEvents)
return;
alreadyHookedScrollEvents = true;
//This is the key player which holds the magic for this trick
//This ScrollViewer is the first templated child of your List
ScrollViewer viewer = FindSimpleVisualChild<ScrollViewer>(theList);
if (viewer != null)
{
// Visual States are always on the first child of the control template
FrameworkElement element = VisualTreeHelper.GetChild(viewer, 0) as FrameworkElement;
if (element != null)
{
VisualStateGroup group = FindVisualState(element, "ScrollStates");
if (group != null)
{
group.CurrentStateChanging += group_CurrentStateChanging;
}
}
}
}
4. Use this helper function to identify the first visual child (ScrollViewer):
T FindSimpleVisualChild<T>(DependencyObject element) where T : class
{
while (element != null)
{
if (element is T)
return element as T;
element = VisualTreeHelper.GetChild(element, 0);
}
return null;
}
5. Actual even handler which identify a changed state for scrollviewer:
void group_CurrentStateChanging(object sender, VisualStateChangedEventArgs e)
{
//for demonstration change page's title
PageTitle.Text = e.NewState.Name;
}
6. Helper function to filter out the required VisualState:
VisualStateGroup FindVisualState(FrameworkElement element, string name)
{
if (element == null)
return null;
IList<VisualStateGroup> groups = (IList<VisualStateGroup>)VisualStateManager.GetVisualStateGroups(element);
foreach (VisualStateGroup group in groups)
if (group.Name == name)
return group;
return null;
}
7. Another helper function to fill the data in list to demonstrate implementation:
ObservableCollection<int> GetListData(int count)
{
sourceList = new ObservableCollection<int>();
for (int i = 1; i <= count; i++)
{
sourceList.Add(i);
}
return sourceList;
}
