WPF ListBox OnScroll Event

Question

I am trying to figure out how to do something that (should) be fairly simple.

What I want is to get an event to fire anytime a ListBox control is scrolled. The ListBox is dynamically created, so I need a way to do it from the code behind (however XAML solutions are appreciated as well, as it gives me something to start from).

Thanks in advance for any ideas.

archer · Accepted Answer · 2018-06-08 19:35:45Z

15

In XAML you can access the ScrollViewer and add events like this:

<ListBox Name="listBox" ScrollViewer.ScrollChanged="listBox_ScrollChanged"/>

Update
This is probably what you need in code behind:

List<ScrollBar> scrollBarList = GetVisualChildCollection<ScrollBar>(listBox);
foreach (ScrollBar scrollBar in scrollBarList)
{
    if (scrollBar.Orientation == Orientation.Horizontal)
    {
        scrollBar.ValueChanged += new RoutedPropertyChangedEventHandler<double>(listBox_HorizontalScrollBar_ValueChanged);
    }
    else
    {
        scrollBar.ValueChanged += new RoutedPropertyChangedEventHandler<double>(listBox_VerticalScrollBar_ValueChanged);
    }
}

With an implementation of GetVisualChildCollection:

public static List<T> GetVisualChildCollection<T>(object parent) where T : Visual
{
    List<T> visualCollection = new List<T>();
    GetVisualChildCollection(parent as DependencyObject, visualCollection);
    return visualCollection;
}
private static void GetVisualChildCollection<T>(DependencyObject parent, List<T> visualCollection) where T : Visual
{
    int count = VisualTreeHelper.GetChildrenCount(parent);
    for (int i = 0; i < count; i++)
    {
        DependencyObject child = VisualTreeHelper.GetChild(parent, i);
        if (child is T)
        {
            visualCollection.Add(child as T);
        }
        else if (child != null)
        {
            GetVisualChildCollection(child, visualCollection);
        }
    }
}

edited Jun 8, 2018 at 19:35

archer

2942 silver badges16 bronze badges

answered Nov 9, 2010 at 22:53

Fredrik Hedblad

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1 Comment

riwalk Over a year ago

Very nice answer. I haven't had the time to implement it to see if it does everything correctly, but it sure sounds right. Thank you for your help.

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