Lazy loading of non-visible elements

Question

I have a case where I have either a gridview/listbox/any type of items control and the number of items bound to the control is massive (easily arou

Answer 1

Here is an event that will notify when user scrolls into the last screen of data:

using System.Windows;
using System.Windows.Controls;

public static class ScrollViewer
{
    public static readonly RoutedEvent LastPageEvent = EventManager.RegisterRoutedEvent(
        "LastPage",
        RoutingStrategy.Bubble,
        typeof(RoutedEventHandler),
        typeof(ScrollViewer));

    private static readonly RoutedEventArgs EventArgs = new RoutedEventArgs(LastPageEvent);

    static ScrollViewer()
    {
        EventManager.RegisterClassHandler(
            typeof(System.Windows.Controls.ScrollViewer),
            System.Windows.Controls.ScrollViewer.ScrollChangedEvent,
            new ScrollChangedEventHandler(OnScrollChanged));
    }
    public static void AddLastPageHandler(UIElement e, RoutedEventHandler handler)
    {
        e.AddHandler(LastPageEvent, handler);
    }

    public static void RemoveLastPageHandler(UIElement e, RoutedEventHandler handler)
    {
        e.RemoveHandler(LastPageEvent, handler);
    }

    private static void OnScrollChanged(object sender, ScrollChangedEventArgs e)
    {
        if (e.ViewportHeight == 0 || e.VerticalOffset == 0)
        {
            return;
        }

        var verticalSpaceLeft = e.ExtentHeight - e.VerticalOffset;
        if (verticalSpaceLeft < 2 * e.ViewportHeight)
        {
            var scrollViewer = (System.Windows.Controls.ScrollViewer)sender;
            scrollViewer.RaiseEvent(EventArgs);
        }
    }
}