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using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Input;
using System.Windows.Media;
namespace Juick.Classes
{
public class ScrollViewerMonitor
{
public static DependencyProperty AtEndCommandProperty =
DependencyProperty.RegisterAttached("AtEndCommand", typeof(ICommand), typeof(ScrollViewerMonitor), new PropertyMetadata(OnAtEndCommandChanged));
public static ICommand GetAtEndCommand(DependencyObject obj)
{
return (ICommand)obj.GetValue(AtEndCommandProperty);
}
public static void SetAtEndCommand(DependencyObject obj, ICommand value)
{
obj.SetValue(AtEndCommandProperty, value);
}
public static void OnAtEndCommandChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
var element = (FrameworkElement)d;
if (element != null)
{
element.Loaded -= element_Loaded;
element.Loaded += element_Loaded;
}
}
static void element_Loaded(object sender, RoutedEventArgs e)
{
var element = (FrameworkElement)sender;
element.Loaded -= element_Loaded;
var scrollViewer = FindChildOfType<ScrollViewer>(element);
if (scrollViewer == null)
{
throw new InvalidOperationException("ScrollViewer not found.");
}
var listener = new DependencyPropertyListener();
listener.Changed += (s, eArgs) =>
{
var atBottom = scrollViewer.VerticalOffset >= scrollViewer.ScrollableHeight;
if (atBottom)
{
var atEnd = GetAtEndCommand(element);
if (atEnd != null && atEnd.CanExecute(null))
{
atEnd.Execute(null);
}
}
};
var binding = new Binding("VerticalOffset") { Source = scrollViewer };
listener.Attach(scrollViewer, binding);
}
static T FindChildOfType<T>(DependencyObject root)
where T : class
{
var queue = new Queue<DependencyObject>();
queue.Enqueue(root);
while (queue.Count > 0)
{
var current = queue.Dequeue();
for (int i = VisualTreeHelper.GetChildrenCount(current) - 1; 0 <= i; i--)
{
var child = VisualTreeHelper.GetChild(current, i);
var typedChild = child as T;
if (typedChild != null)
{
return typedChild;
}
queue.Enqueue(child);
}
}
return null;
}
}
}
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