145 lines
5.1 KiB
C#
145 lines
5.1 KiB
C#
using System;
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using System.Collections;
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using System.Collections.Specialized;
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using System.Windows;
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using System.Windows.Controls;
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using System.Windows.Data;
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using System.Windows.Media;
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// ReSharper disable UnusedMember.Global - public API
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namespace PettingZoo.UI
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{
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// Source: https://social.msdn.microsoft.com/Forums/vstudio/en-US/0f524459-b14e-4f9a-8264-267953418a2d/trivial-listboxlistview-autoscroll?forum=wpf
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//
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// Slightly modified version; takes into account the current scroll position of the ListBox,
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// so the end user can scroll up without getting dragged down again.
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public static class ListBox
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{
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public static readonly DependencyProperty AutoScrollProperty =
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DependencyProperty.RegisterAttached("AutoScroll", typeof (bool), typeof (System.Windows.Controls.ListBox),
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new PropertyMetadata(false));
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public static readonly DependencyProperty AutoScrollHandlerProperty =
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DependencyProperty.RegisterAttached("AutoScrollHandler", typeof (AutoScrollHandler),
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typeof (System.Windows.Controls.ListBox));
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public static bool GetAutoScroll(System.Windows.Controls.ListBox instance)
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{
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return (bool) instance.GetValue(AutoScrollProperty);
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}
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public static void SetAutoScroll(System.Windows.Controls.ListBox instance, bool value)
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{
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var oldHandler = (AutoScrollHandler?)instance.GetValue(AutoScrollHandlerProperty);
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if (oldHandler != null)
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{
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oldHandler.Dispose();
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instance.SetValue(AutoScrollHandlerProperty, null);
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}
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instance.SetValue(AutoScrollProperty, value);
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if (value)
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instance.SetValue(AutoScrollHandlerProperty, new AutoScrollHandler(instance));
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}
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}
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public class AutoScrollHandler : DependencyObject, IDisposable
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{
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public static readonly DependencyProperty ItemsSourceProperty =
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DependencyProperty.Register("ItemsSource", typeof (IEnumerable),
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typeof (AutoScrollHandler), new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.None,
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ItemsSourcePropertyChanged));
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private readonly System.Windows.Controls.ListBox target;
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private ScrollViewer? scrollViewer;
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public AutoScrollHandler(System.Windows.Controls.ListBox target)
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{
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this.target = target;
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var binding = new Binding("ItemsSource")
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{
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Source = this.target
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};
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BindingOperations.SetBinding(this, ItemsSourceProperty, binding);
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}
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public void Dispose()
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{
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BindingOperations.ClearBinding(this, ItemsSourceProperty);
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GC.SuppressFinalize(this);
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}
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public IEnumerable ItemsSource
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{
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get => (IEnumerable) GetValue(ItemsSourceProperty);
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set => SetValue(ItemsSourceProperty, value);
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}
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private static void ItemsSourcePropertyChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
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{
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((AutoScrollHandler) o).ItemsSourceChanged((IEnumerable) e.OldValue, (IEnumerable) e.NewValue);
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}
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private void ItemsSourceChanged(IEnumerable oldValue, IEnumerable newValue)
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{
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if (oldValue is INotifyCollectionChanged oldCollection)
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oldCollection.CollectionChanged -= Collection_CollectionChanged;
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if (newValue is INotifyCollectionChanged newCollection)
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newCollection.CollectionChanged += Collection_CollectionChanged;
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}
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private void Collection_CollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
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{
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if (e.Action != NotifyCollectionChangedAction.Add || e.NewItems == null || e.NewItems.Count < 1)
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return;
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// Resolve on demand; in the constructor FindScrollViewer will return null
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if (scrollViewer == null)
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{
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scrollViewer = FindScrollViewer(target);
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if (scrollViewer == null)
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return;
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}
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if (e.NewItems.Count == 0)
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return;
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// If not already at the bottom, keep the position stable
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if (Math.Abs(scrollViewer.VerticalOffset - scrollViewer.ScrollableHeight) > 0)
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return;
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var item = e.NewItems[^1];
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if (item != null)
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target.ScrollIntoView(item);
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}
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private static ScrollViewer? FindScrollViewer(DependencyObject parent)
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{
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var childCount = VisualTreeHelper.GetChildrenCount(parent);
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for (var childIndex = 0; childIndex < childCount; childIndex++)
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{
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var child = VisualTreeHelper.GetChild(parent, childIndex);
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if (child is ScrollViewer scrollViewer)
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return scrollViewer;
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var childScrollViewer = FindScrollViewer(child);
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if (childScrollViewer != null)
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return childScrollViewer;
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}
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return null;
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}
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}
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}
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