diff options
Diffstat (limited to 'Juick/Classes/ScrollViewerMonitor.cs')
-rw-r--r-- | Juick/Classes/ScrollViewerMonitor.cs | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/Juick/Classes/ScrollViewerMonitor.cs b/Juick/Classes/ScrollViewerMonitor.cs new file mode 100644 index 0000000..6a65773 --- /dev/null +++ b/Juick/Classes/ScrollViewerMonitor.cs @@ -0,0 +1,86 @@ +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; + } + } +} |