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-rw-r--r--Juick/Classes/DeferredLoadListBox.cs275
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diff --git a/Juick/Classes/DeferredLoadListBox.cs b/Juick/Classes/DeferredLoadListBox.cs
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--- a/Juick/Classes/DeferredLoadListBox.cs
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-// Copyright (C) Microsoft Corporation. All Rights Reserved.
-// This code released under the terms of the Microsoft Public License
-// (Ms-PL, http://opensource.org/licenses/ms-pl.html).
-
-using System;
-using System.Collections.Generic;
-using System.ComponentModel;
-using System.Windows;
-using System.Windows.Controls;
-using System.Windows.Controls.Primitives;
-using System.Windows.Data;
-using System.Windows.Media;
-
-namespace Juick.Classes
-{
- /// <summary>
- /// Implements a subclass of ListBox based on a StackPanel that defers the
- /// loading of off-screen items until necessary in order to minimize impact
- /// to the UI thread.
- /// </summary>
- public class DeferredLoadListBox : ListBox
- {
- private enum OverlapKind { Overlap, ChildAbove, ChildBelow };
-
- private ScrollViewer _scrollViewer;
- private ItemContainerGenerator _generator;
- private bool _queuedUnmaskVisibleContent;
- private bool _inOnApplyTemplate;
-
- /// <summary>
- /// Handles the application of the Control's Template.
- /// </summary>
- public override void OnApplyTemplate()
- {
- // Unhook from old Template elements
- _inOnApplyTemplate = true;
- ClearValue(VerticalOffsetShadowProperty);
- _scrollViewer = null;
- _generator = null;
-
- // Apply new Template
- base.OnApplyTemplate();
-
- // Hook up to new Template elements
- _scrollViewer = FindFirstChildOfType<ScrollViewer>(this);
- if (null == _scrollViewer)
- {
- throw new NotSupportedException("Control Template must include a ScrollViewer (wrapping ItemsHost).");
- }
- _generator = ItemContainerGenerator;
- SetBinding(VerticalOffsetShadowProperty, new Binding { Source = _scrollViewer, Path = new PropertyPath("VerticalOffset") });
- _inOnApplyTemplate = false;
- }
-
- /// <summary>
- /// Determines if the specified item is (or is eligible to be) its own item container.
- /// </summary>
- /// <param name="item">The specified item.</param>
- /// <returns>true if the item is its own item container; otherwise, false.</returns>
- protected override bool IsItemItsOwnContainerOverride(object item)
- {
- // Check container type
- return item is DeferredLoadListBoxItem;
- }
-
- /// <summary>
- /// Creates or identifies the element used to display a specified item.
- /// </summary>
- /// <returns>A DeferredLoadListBoxItem corresponding to a specified item.</returns>
- protected override DependencyObject GetContainerForItemOverride()
- {
- // Create container (matches ListBox implementation)
- var item = new DeferredLoadListBoxItem();
- if (ItemContainerStyle != null)
- {
- item.Style = ItemContainerStyle;
- }
- return item;
- }
-
- /// <summary>
- /// Prepares the specified element to display the specified item.
- /// </summary>
- /// <param name="element">The element used to display the specified item.</param>
- /// <param name="item">The item to display.</param>
- protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
- {
- // Perform base class preparation
- base.PrepareContainerForItemOverride(element, item);
-
- // Mask the container's content
- var container = (DeferredLoadListBoxItem)element;
- if (!DesignerProperties.IsInDesignTool)
- {
- container.MaskContent();
- }
-
- // Queue a (single) pass to unmask newly visible content on the next tick
- if (!_queuedUnmaskVisibleContent)
- {
- _queuedUnmaskVisibleContent = true;
- Dispatcher.BeginInvoke(() =>
- {
- _queuedUnmaskVisibleContent = false;
- UnmaskVisibleContent();
- });
- }
- }
-
- private static readonly DependencyProperty VerticalOffsetShadowProperty =
- DependencyProperty.Register("VerticalOffsetShadow", typeof(double), typeof(DeferredLoadListBox), new PropertyMetadata(-1.0, OnVerticalOffsetShadowChanged));
- private static void OnVerticalOffsetShadowChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
- {
- // Handle ScrollViewer VerticalOffset change by unmasking newly visible content
- ((DeferredLoadListBox)o).UnmaskVisibleContent();
- }
-
- private void UnmaskVisibleContent()
- {
- // Capture variables
- var count = Items.Count;
-
- // Find index of any container within view using (1-indexed) binary search
- var index = -1;
- var l = 0;
- var r = count + 1;
- while (-1 == index)
- {
- var p = (r - l) / 2;
- if (0 == p)
- {
- break;
- }
- p += l;
- var c = (DeferredLoadListBoxItem)_generator.ContainerFromIndex(p - 1);
- if (null == c)
- {
- if (_inOnApplyTemplate)
- {
- // Applying template; don't expect to have containers at this point
- return;
- }
- // Should always be able to get the container
- var presenter = FindFirstChildOfType<ItemsPresenter>(_scrollViewer);
- var panel = (null == presenter) ? null : FindFirstChildOfType<Panel>(presenter);
- if (panel is VirtualizingStackPanel)
- {
- throw new NotSupportedException("Must change ItemsPanel to be a StackPanel (via the ItemsPanel property).");
- }
- else
- {
- throw new NotSupportedException("Couldn't find container for item (ItemsPanel should be a StackPanel).");
- }
- }
- switch (Overlap(_scrollViewer, c, 0))
- {
- case OverlapKind.Overlap:
- index = p - 1;
- break;
- case OverlapKind.ChildAbove:
- l = p;
- break;
- case OverlapKind.ChildBelow:
- r = p;
- break;
- }
- }
-
- if (-1 != index)
- {
- // Unmask visible items below the current item
- for (var i = index; i < count; i++)
- {
- if (!UnmaskItemContent(i))
- {
- break;
- }
- }
-
- // Unmask visible items above the current item
- for (var i = index - 1; 0 <= i; i--)
- {
- if (!UnmaskItemContent(i))
- {
- break;
- }
- }
- }
- }
-
- private bool UnmaskItemContent(int index)
- {
- var container = (DeferredLoadListBoxItem)_generator.ContainerFromIndex(index);
- if (null != container)
- {
- // Return quickly if not masked (but periodically check visibility anyway so we can stop once we're out of range)
- if (!container.Masked && (0 != (index % 16)))
- {
- return true;
- }
- // Check necessary conditions
- if (0 == container.ActualHeight)
- {
- // In some cases, ActualHeight will be 0 here, but can be "fixed" with an explicit call to UpdateLayout
- container.UpdateLayout();
- if (0 == container.ActualHeight)
- {
- throw new NotSupportedException("All containers must have a Height set (ex: via ItemContainerStyle), though the heights do not all need to be the same.");
- }
- }
- // If container overlaps the "visible" area (i.e. on or near the screen), unmask it
- if (OverlapKind.Overlap == Overlap(_scrollViewer, container, 2 * _scrollViewer.ActualHeight))
- {
- container.UnmaskContent();
- return true;
- }
- }
- return false;
- }
-
- private static bool Overlap(double startA, double endA, double startB, double endB)
- {
- return (((startA <= startB) && (startB <= endA)) ||
- ((startB <= startA) && (startA <= endB)));
- }
-
- private static OverlapKind Overlap(ScrollViewer parent, FrameworkElement child, double padding)
- {
- // Get child transform relative to parent
- //var transform = child.TransformToVisual(parent); // Unreliable on Windows Phone 7; throws ArgumentException sometimes
- var layoutSlot = LayoutInformation.GetLayoutSlot(child);
- var transform = new TranslateTransform { /*X = layoutSlot.Left - parent.HorizontalOffset,*/ Y = layoutSlot.Top - parent.VerticalOffset };
- // Get child bounds relative to parent
- var bounds = new Rect(transform.Transform(new Point()), transform.Transform(new Point(/*child.ActualWidth*/ 0, child.ActualHeight)));
- // Return kind of overlap
- if (Overlap(0 - padding, parent.ActualHeight + padding, bounds.Top, bounds.Bottom))
- {
- return OverlapKind.Overlap;
- }
- else if (bounds.Top < 0)
- {
- return OverlapKind.ChildAbove;
- }
- else
- {
- return OverlapKind.ChildBelow;
- }
- }
-
- private static T FindFirstChildOfType<T>(DependencyObject root) where T : class
- {
- // Enqueue root node
- var queue = new Queue<DependencyObject>();
- queue.Enqueue(root);
- while (0 < queue.Count)
- {
- // Dequeue next node and check its children
- var current = queue.Dequeue();
- for (var i = VisualTreeHelper.GetChildrenCount(current) - 1; 0 <= i; i--)
- {
- var child = VisualTreeHelper.GetChild(current, i);
- var typedChild = child as T;
- if (null != typedChild)
- {
- return typedChild;
- }
- // Enqueue child
- queue.Enqueue(child);
- }
- }
- // No children match
- return null;
- }
- }
-}
generated by cgit v1.2.3 (git 2.39.1) at 2024-05-18 07:14:06 +0000