Code:
/ DotNET / DotNET / 8.0 / untmp / WIN_WINDOWS / lh_tools_devdiv_wpf / Windows / wcp / Framework / System / Windows / Controls / VirtualizingStackPanel.cs / 4 / VirtualizingStackPanel.cs
//----------------------------------------------------------------------------
//
// Copyright (C) Microsoft Corporation. All rights reserved.
//
//---------------------------------------------------------------------------
//#define Profiling
using MS.Internal;
using MS.Utility;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Diagnostics;
using System.Windows.Controls.Primitives;
using System.Windows.Media;
using System.Windows.Threading;
using System.Windows.Input;
namespace System.Windows.Controls
{
///
/// VirtualizingStackPanel is used to arrange children into single line.
///
public class VirtualizingStackPanel : VirtualizingPanel, IScrollInfo
{
//-------------------------------------------------------------------
//
// Constructors
//
//-------------------------------------------------------------------
#region Constructors
///
/// Default constructor.
///
public VirtualizingStackPanel()
{
}
#endregion Constructors
//--------------------------------------------------------------------
//
// Public Methods
//
//-------------------------------------------------------------------
#region Public Methods
//------------------------------------------------------------
// IScrollInfo Methods
//------------------------------------------------------------
#region IScrollInfo Methods
///
/// Scroll content by one line to the top.
///
public void LineUp()
{
SetVerticalOffset(VerticalOffset - ((Orientation == Orientation.Vertical) ? 1.0 : ScrollViewer._scrollLineDelta));
}
///
/// Scroll content by one line to the bottom.
///
public void LineDown()
{
SetVerticalOffset(VerticalOffset + ((Orientation == Orientation.Vertical) ? 1.0 : ScrollViewer._scrollLineDelta));
}
///
/// Scroll content by one line to the left.
///
public void LineLeft()
{
SetHorizontalOffset(HorizontalOffset - ((Orientation == Orientation.Horizontal) ? 1.0 : ScrollViewer._scrollLineDelta));
}
///
/// Scroll content by one line to the right.
///
public void LineRight()
{
SetHorizontalOffset(HorizontalOffset + ((Orientation == Orientation.Horizontal) ? 1.0 : ScrollViewer._scrollLineDelta));
}
///
/// Scroll content by one page to the top.
///
public void PageUp()
{
SetVerticalOffset(VerticalOffset - ViewportHeight);
}
///
/// Scroll content by one page to the bottom.
///
public void PageDown()
{
SetVerticalOffset(VerticalOffset + ViewportHeight);
}
///
/// Scroll content by one page to the left.
///
public void PageLeft()
{
SetHorizontalOffset(HorizontalOffset - ViewportWidth);
}
///
/// Scroll content by one page to the right.
///
public void PageRight()
{
SetHorizontalOffset(HorizontalOffset + ViewportWidth);
}
///
/// Scroll content by one page to the top.
///
public void MouseWheelUp()
{
SetVerticalOffset(VerticalOffset - SystemParameters.WheelScrollLines * ((Orientation == Orientation.Vertical) ? 1.0 : ScrollViewer._scrollLineDelta));
}
///
/// Scroll content by one page to the bottom.
///
public void MouseWheelDown()
{
SetVerticalOffset(VerticalOffset + SystemParameters.WheelScrollLines * ((Orientation == Orientation.Vertical) ? 1.0 : ScrollViewer._scrollLineDelta));
}
///
/// Scroll content by one page to the left.
///
public void MouseWheelLeft()
{
SetHorizontalOffset(HorizontalOffset - 3.0 * ((Orientation == Orientation.Horizontal) ? 1.0 : ScrollViewer._scrollLineDelta));
}
///
/// Scroll content by one page to the right.
///
public void MouseWheelRight()
{
SetHorizontalOffset(HorizontalOffset + 3.0 * ((Orientation == Orientation.Horizontal) ? 1.0 : ScrollViewer._scrollLineDelta));
}
///
/// Set the HorizontalOffset to the passed value.
///
public void SetHorizontalOffset(double offset)
{
EnsureScrollData();
double scrollX = ScrollContentPresenter.ValidateInputOffset(offset, "HorizontalOffset");
if (!DoubleUtil.AreClose(scrollX, _scrollData._offset.X))
{
_scrollData._offset.X = scrollX;
InvalidateMeasure();
}
}
///
/// Set the VerticalOffset to the passed value.
///
public void SetVerticalOffset(double offset)
{
EnsureScrollData();
double scrollY = ScrollContentPresenter.ValidateInputOffset(offset, "VerticalOffset");
if (!DoubleUtil.AreClose(scrollY, _scrollData._offset.Y))
{
_scrollData._offset.Y = scrollY;
InvalidateMeasure();
}
}
///
/// VirtualizingStackPanel implementation of
// The goal is to change offsets to bring the child into view, and return a rectangle in our space to make visible.
// The rectangle we return is in the physical dimension the input target rect transformed into our pace.
// In the logical dimension, it is our immediate child's rect.
// Note: This code presently assumes we/children are layout clean. See work item 22269 for more detail.
public Rect MakeVisible(Visual visual, Rect rectangle)
{
Vector newOffset = new Vector();
Rect newRect = new Rect();
Rect originalRect = rectangle;
// We can only work on visuals that are us or children.
// An empty rect has no size or position. We can't meaningfully use it.
if ( rectangle.IsEmpty
|| visual == null
|| visual == (Visual)this
|| !this.IsAncestorOf(visual))
{
return Rect.Empty;
}
#pragma warning disable 1634, 1691
#pragma warning disable 56506
// Compute the child's rect relative to (0,0) in our coordinate space.
// This is a false positive by PreSharp. visual cannot be null because of the 'if' check above
GeneralTransform childTransform = visual.TransformToAncestor(this);
#pragma warning restore 56506
#pragma warning restore 1634, 1691
rectangle = childTransform.TransformBounds(rectangle);
// We can't do any work unless we're scrolling.
if (!IsScrolling)
{
return rectangle;
}
// Bring the target rect into view in the physical dimension.
MakeVisiblePhysicalHelper(rectangle, ref newOffset, ref newRect);
// Bring our child containing the visual into view.
int childIndex = FindChildIndexThatParentsVisual(visual);
MakeVisibleLogicalHelper(childIndex, rectangle, ref newOffset, ref newRect);
// We have computed the scrolling offsets; validate and scroll to them.
newOffset.X = ScrollContentPresenter.CoerceOffset(newOffset.X, _scrollData._extent.Width, _scrollData._viewport.Width);
newOffset.Y = ScrollContentPresenter.CoerceOffset(newOffset.Y, _scrollData._extent.Height, _scrollData._viewport.Height);
if (!DoubleUtil.AreClose(newOffset, _scrollData._offset))
{
_scrollData._offset = newOffset;
InvalidateMeasure();
OnScrollChange();
if (ScrollOwner != null)
{
// When layout gets updated it may happen that visual is obscured by a ScrollBar
// We call MakeVisible again to make sure element is visible in this case
ScrollOwner.MakeVisible(visual, originalRect);
}
}
// Return the rectangle
return newRect;
}
///
/// Generates the item at the specified index and calls BringIntoView on it.
///
/// Specify the item index that should become visible
///
/// Thrown if index is out of range
///
protected internal override void BringIndexIntoView(int index)
{
UIElementCollection children = InternalChildren;
if (index < 0 || index >= ItemCount)
throw new ArgumentOutOfRangeException("index");
IItemContainerGenerator generator = Generator;
int childIndex;
GeneratorPosition position = IndexToGeneratorPositionForStart(index, out childIndex);
using (generator.StartAt(position, GeneratorDirection.Forward, true))
{
bool newlyRealized;
UIElement child = generator.GenerateNext(out newlyRealized) as UIElement;
if (child != null)
{
if (newlyRealized)
{
// A new container was generated, update the generated state
if (childIndex >= children.Count)
{
VirtualizingPanel.AddInternalChild(children, child);
}
else
{
VirtualizingPanel.InsertInternalChild(children, childIndex, child);
if (childIndex <= _firstVisibleChildIndex)
{
_firstVisibleChildIndex++;
}
}
generator.PrepareItemContainer(child);
}
FrameworkElement element = child as FrameworkElement;
if (element != null)
{
element.BringIntoView();
}
}
}
}
#endregion
#endregion
//-------------------------------------------------------------------
//
// Public Properties
//
//--------------------------------------------------------------------
#region Public Properties
///
/// Specifies dimension of children stacking.
///
public Orientation Orientation
{
get { return (Orientation) GetValue(OrientationProperty); }
set { SetValue(OrientationProperty, value); }
}
///
/// This property is always true because this panel has vertical or horizontal orientation
///
protected internal override bool HasLogicalOrientation
{
get { return true; }
}
///
/// Orientation of the panel if its layout is in one dimension.
/// Otherwise HasLogicalOrientation is false and LogicalOrientation should be ignored
///
protected internal override Orientation LogicalOrientation
{
get { return this.Orientation; }
}
///
/// DependencyProperty for
public static readonly DependencyProperty OrientationProperty =
DependencyProperty.Register("Orientation", typeof(Orientation), typeof(VirtualizingStackPanel),
new FrameworkPropertyMetadata(Orientation.Vertical,
FrameworkPropertyMetadataOptions.AffectsMeasure,
new PropertyChangedCallback(OnOrientationChanged)),
new ValidateValueCallback(ScrollBar.IsValidOrientation));
///
/// Attached property for use on the ItemsControl that is the host for the items being
/// presented by this panel. Use this property to turn virtualization on/off.
///
public static readonly DependencyProperty IsVirtualizingProperty =
DependencyProperty.RegisterAttached("IsVirtualizing", typeof(bool), typeof(VirtualizingStackPanel),
new FrameworkPropertyMetadata(true));
///
/// Retrieves the value for
/// The object on which to query the value.
/// True if virtualizing, false otherwise.
public static bool GetIsVirtualizing(DependencyObject o)
{
if (o == null)
{
throw new ArgumentNullException("o");
}
return (bool)o.GetValue(IsVirtualizingProperty);
}
///
/// Sets the value for
/// The element on which to set the value.
/// True if virtualizing, false otherwise.
public static void SetIsVirtualizing(DependencyObject element, bool value)
{
if (element == null)
{
throw new ArgumentNullException("element");
}
element.SetValue(IsVirtualizingProperty, value);
}
//-----------------------------------------------------------
// IScrollInfo Properties
//-----------------------------------------------------------
#region IScrollInfo Properties
///
/// VirtualizingStackPanel reacts to this property by changing it's child measurement algorithm.
/// If scrolling in a dimension, infinite space is allowed the child; otherwise, available size is preserved.
///
[DefaultValue(false)]
public bool CanHorizontallyScroll
{
get
{
if (_scrollData == null) { return false; }
return _scrollData._allowHorizontal;
}
set
{
EnsureScrollData();
if (_scrollData._allowHorizontal != value)
{
_scrollData._allowHorizontal = value;
InvalidateMeasure();
}
}
}
///
/// VirtualizingStackPanel reacts to this property by changing it's child measurement algorithm.
/// If scrolling in a dimension, infinite space is allowed the child; otherwise, available size is preserved.
///
[DefaultValue(false)]
public bool CanVerticallyScroll
{
get
{
if (_scrollData == null) { return false; }
return _scrollData._allowVertical;
}
set
{
EnsureScrollData();
if (_scrollData._allowVertical != value)
{
_scrollData._allowVertical = value;
InvalidateMeasure();
}
}
}
///
/// ExtentWidth contains the horizontal size of the scrolled content element in 1/96"
///
public double ExtentWidth
{
get
{
if (_scrollData == null) { return 0.0; }
return _scrollData._extent.Width;
}
}
///
/// ExtentHeight contains the vertical size of the scrolled content element in 1/96"
///
public double ExtentHeight
{
get
{
if (_scrollData == null) { return 0.0; }
return _scrollData._extent.Height;
}
}
///
/// ViewportWidth contains the horizontal size of content's visible range in 1/96"
///
public double ViewportWidth
{
get
{
if (_scrollData == null) { return 0.0; }
return _scrollData._viewport.Width;
}
}
///
/// ViewportHeight contains the vertical size of content's visible range in 1/96"
///
public double ViewportHeight
{
get
{
if (_scrollData == null) { return 0.0; }
return _scrollData._viewport.Height;
}
}
///
/// HorizontalOffset is the horizontal offset of the scrolled content in 1/96".
///
[DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
public double HorizontalOffset
{
get
{
if (_scrollData == null) { return 0.0; }
return _scrollData._computedOffset.X;
}
}
///
/// VerticalOffset is the vertical offset of the scrolled content in 1/96".
///
[DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
public double VerticalOffset
{
get
{
if (_scrollData == null) { return 0.0; }
return _scrollData._computedOffset.Y;
}
}
///
/// ScrollOwner is the container that controls any scrollbars, headers, etc... that are dependant
/// on this IScrollInfo's properties.
///
[DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
public ScrollViewer ScrollOwner
{
get
{
EnsureScrollData();
return _scrollData._scrollOwner;
}
set
{
EnsureScrollData();
if (value != _scrollData._scrollOwner)
{
ResetScrolling(this);
_scrollData._scrollOwner = value;
}
}
}
#endregion IScrollInfo Properties
#endregion Public Properties
//-------------------------------------------------------------------
//
// Public Events
//
//--------------------------------------------------------------------
#region Public Events
///
/// Called on the ItemsControl that owns this panel when an item is being re-virtualized.
///
public static readonly RoutedEvent CleanUpVirtualizedItemEvent = EventManager.RegisterRoutedEvent("CleanUpVirtualizedItemEvent", RoutingStrategy.Direct, typeof(CleanUpVirtualizedItemEventHandler), typeof(VirtualizingStackPanel));
///
/// Adds a handler for the CleanUpVirtualizedItem attached event
///
/// DependencyObject that listens to this event
/// Event Handler to be added
public static void AddCleanUpVirtualizedItemHandler(DependencyObject element, CleanUpVirtualizedItemEventHandler handler)
{
FrameworkElement.AddHandler(element, CleanUpVirtualizedItemEvent, handler);
}
///
/// Removes a handler for the CleanUpVirtualizedItem attached event
///
/// DependencyObject that listens to this event
/// Event Handler to be removed
public static void RemoveCleanUpVirtualizedItemHandler(DependencyObject element, CleanUpVirtualizedItemEventHandler handler)
{
FrameworkElement.RemoveHandler(element, CleanUpVirtualizedItemEvent, handler);
}
///
/// Called when an item is being re-virtualized.
///
protected virtual void OnCleanUpVirtualizedItem(CleanUpVirtualizedItemEventArgs e)
{
ItemsControl itemsControl = ItemsControl.GetItemsOwner(this);
if (itemsControl != null)
{
itemsControl.RaiseEvent(e);
}
}
#endregion
//-------------------------------------------------------------------
//
// Protected Methods
//
//--------------------------------------------------------------------
#region Protected Methods
///
/// General VirtualizingStackPanel layout behavior is to grow unbounded in the "stacking" direction (Size To Content).
/// Children in this dimension are encouraged to be as large as they like. In the other dimension,
/// VirtualizingStackPanel will assume the maximum size of its children.
///
///
/// When scrolling, VirtualizingStackPanel will not grow in layout size but effectively add the children on a z-plane which
/// will probably be clipped by some parent (typically a ScrollContentPresenter) to Stack's size.
///
/// Constraint
/// Desired size
protected override Size MeasureOverride(Size constraint)
{
#if Profiling
if (Panel.IsAboutToGenerateContent(this))
return MeasureOverrideProfileStub(constraint);
else
return RealMeasureOverride(constraint);
}
// this is a handy place to start/stop profiling
private Size MeasureOverrideProfileStub(Size constraint)
{
return RealMeasureOverride(constraint);
}
private Size RealMeasureOverride(Size constraint)
{
#endif
UIElementCollection children = InternalChildren;
Size stackDesiredSize = new Size();
Size layoutSlotSize = constraint;
bool fHorizontal = (Orientation == Orientation.Horizontal);
int firstViewport; // First child index in the viewport.
int lastViewport = -1; // Last child index in the viewport. -1 indicates we have not yet iterated through the last child.
double logicalVisibleSpace, childLogicalSize;
bool etwTracingEnabled = IsScrolling && EventTrace.IsEnabled(EventTrace.Flags.performance, EventTrace.Level.normal);
if (etwTracingEnabled)
{
EventTrace.EventProvider.TraceEvent(EventTrace.GuidFromId(EventTraceGuidId.GENERICSTRINGGUID), MS.Utility.EventType.StartEvent, "VirtualizingStackPanel :MeasureOverride");
}
//
// Collect information from the ItemsControl, if there is one.
//
IItemContainerGenerator generator = Generator;
ItemsControl itemsControl = ItemsControl.GetItemsOwner(this);
int itemCount = (itemsControl != null) ? itemsControl.Items.Count : 0;
bool isVirtualizing = (itemsControl != null) ? GetIsVirtualizing(itemsControl) : true;
//
// Initialize child sizing and iterator data
// Allow children as much size as they want along the stack.
//
if (fHorizontal)
{
layoutSlotSize.Width = Double.PositiveInfinity;
if (IsScrolling && CanVerticallyScroll) { layoutSlotSize.Height = Double.PositiveInfinity; }
firstViewport = (IsScrolling) ? CoerceOffsetToInteger(_scrollData._offset.X, itemCount) : 0;
logicalVisibleSpace = constraint.Width;
}
else
{
layoutSlotSize.Height = Double.PositiveInfinity;
if (IsScrolling && CanHorizontallyScroll) { layoutSlotSize.Width = Double.PositiveInfinity; }
firstViewport = (IsScrolling) ? CoerceOffsetToInteger(_scrollData._offset.Y, itemCount) : 0;
logicalVisibleSpace = constraint.Height;
}
//
// Figure out the position of the first visible item
//
GeneratorPosition startPos = IndexToGeneratorPositionForStart(isVirtualizing ? firstViewport : 0, out _firstVisibleChildIndex);
int childIndex = _firstVisibleChildIndex;
bool ranOutOfItems = true;
_visibleCount = 0;
if (itemCount > 0)
{
_afterTrail = 0;
using (generator.StartAt(startPos, GeneratorDirection.Forward, true))
{
for (int i = isVirtualizing ? firstViewport : 0, count = itemCount; i < count; ++i)
{
// Get next child.
bool newlyRealized;
UIElement child = generator.GenerateNext(out newlyRealized) as UIElement;
if (child == null)
{
Debug.Assert(!newlyRealized, "The generator realized a null value.");
// We reached the end of the items (because of a group)
break;
}
if (!newlyRealized)
{
Debug.Assert(child == children[childIndex], "Wrong child was generated");
Debug.Assert(GetGeneratedIndex(childIndex) == i, "Wrong index for previously generated child");
}
else
{
Debug.Assert(child != null, "Null child was generated");
if (childIndex >= children.Count)
{
VirtualizingPanel.AddInternalChild(children, child);
}
else
{
VirtualizingPanel.InsertInternalChild(children, childIndex, child);
}
generator.PrepareItemContainer(child);
}
childIndex++;
_visibleCount++;
// Measure the child.
Size childDesiredSize = child.DesiredSize;
child.Measure(layoutSlotSize);
if (childDesiredSize != child.DesiredSize)
{
childDesiredSize = child.DesiredSize;
// Reset the _maxDesiredSize cache if child DesiredSize changes
if (_scrollData != null)
_scrollData._maxDesiredSize = new Size();
}
// Accumulate child size.
if (fHorizontal)
{
stackDesiredSize.Width += childDesiredSize.Width;
stackDesiredSize.Height = Math.Max(stackDesiredSize.Height, childDesiredSize.Height);
childLogicalSize = childDesiredSize.Width;
}
else
{
stackDesiredSize.Width = Math.Max(stackDesiredSize.Width, childDesiredSize.Width);
stackDesiredSize.Height += childDesiredSize.Height;
childLogicalSize = childDesiredSize.Height;
}
// Adjust remaining viewport space if we are scrolling and within the viewport region.
// While scrolling (not virtualizing), we always measure children before and after the viewport.
if (IsScrolling && lastViewport == -1 && i >= firstViewport)
{
logicalVisibleSpace -= childLogicalSize;
if (DoubleUtil.LessThanOrClose(logicalVisibleSpace, 0.0))
{
lastViewport = i;
}
}
// When scrolling, virtualizing, and beyond the first element,
// then stop creating elements when out of space.
if (IsScrolling && isVirtualizing && (i > firstViewport))
{
// If begining of the item is outside the constraint
if ((fHorizontal && (stackDesiredSize.Width - childDesiredSize.Width > constraint.Width)) ||
(!fHorizontal && (stackDesiredSize.Height - childDesiredSize.Height > constraint.Height)))
{
// We want to keep a focusable item after the end so that keyboard navigation
// can work, but we want to limit that to FocusTrail number of items
// in case all the items are not focusable.
_afterTrail++;
if ((_afterTrail >= FocusTrail) || Keyboard.IsFocusable(child))
{
// Either we past the limit or the child was focusable
ranOutOfItems = false;
break;
}
// Loop around and generate another item
}
}
}
}
}
_visibleStart = firstViewport;
//
// Compute Scrolling stuff.
//
if (IsScrolling)
{
// Compute viewport and extent.
Size viewport = constraint;
Vector offset = _scrollData._offset;
bool accumulateExtent = false;
if (ScrollOwner != null)
{
accumulateExtent = ScrollOwner.InChildInvalidateMeasure;
ScrollOwner.InChildInvalidateMeasure = false;
}
Size extent = new Size();
if (fHorizontal)
{
extent.Width = itemCount;
extent.Height = accumulateExtent ? Math.Max(stackDesiredSize.Height, _scrollData._extent.Height) : stackDesiredSize.Height;
}
else
{
extent.Width = accumulateExtent ? Math.Max(stackDesiredSize.Width, _scrollData._extent.Width) : stackDesiredSize.Width;
extent.Height = itemCount;
}
// If we have not yet set the last child in the viewport, set it to the last child.
if (lastViewport == -1) { lastViewport = itemCount - 1; }
if (ranOutOfItems)
{
// If we or children have resized, it's possible that we can now display more content.
// This is true if we started at a nonzero offeset and still have space remaining.
// In this case, we loop back through previous children until we run out of space.
childIndex = isVirtualizing ? _firstVisibleChildIndex : firstViewport;
while (childIndex > 0)
{
if (!PreviousChildIsGenerated(childIndex))
{
GeneratePreviousChild(childIndex, layoutSlotSize);
childIndex++; // We just inserted a child, so increment the index
}
else if (childIndex <= _firstVisibleChildIndex)
{
// This child has not been measured yet
children[childIndex - 1].Measure(layoutSlotSize);
}
double projectedLogicalVisibleSpace = logicalVisibleSpace;
Size childDesiredSize = children[childIndex - 1].DesiredSize;
if (fHorizontal)
{
projectedLogicalVisibleSpace -= childDesiredSize.Width;
}
else
{
projectedLogicalVisibleSpace -= childDesiredSize.Height;
}
// If we have run out of room, break.
if (DoubleUtil.LessThan(projectedLogicalVisibleSpace, 0.0)) { break; }
// Account for the child in the panel's desired size
if (fHorizontal)
{
stackDesiredSize.Width += childDesiredSize.Width;
stackDesiredSize.Height = Math.Max(stackDesiredSize.Height, childDesiredSize.Height);
}
else
{
stackDesiredSize.Width = Math.Max(stackDesiredSize.Width, childDesiredSize.Width);
stackDesiredSize.Height += childDesiredSize.Height;
}
// Adjust viewport
childIndex--;
logicalVisibleSpace = projectedLogicalVisibleSpace;
}
if ((childIndex < _firstVisibleChildIndex) || !isVirtualizing)
{
_firstVisibleChildIndex = childIndex;
}
_visibleStart = firstViewport = (GetGeneratedCount(children) == 0) ? 0 : GetGeneratedIndex(_firstVisibleChildIndex);
}
EnsureTopCapGenerated(layoutSlotSize);
int logicalExtent = itemCount;
int logicalViewport = lastViewport - firstViewport;
// We are conservative when estimating a viewport, not including the last element in case it is only partially visible.
// We want to count it if it is fully visible (>= 0 space remaining) or the only element in the viewport.
if (logicalViewport == 0 || DoubleUtil.GreaterThanOrClose(logicalVisibleSpace, 0.0)) { logicalViewport++; }
if (fHorizontal)
{
_scrollData._physicalViewport = viewport.Width;
viewport.Width = logicalViewport;
offset.X = firstViewport;
offset.Y = Math.Max(0, Math.Min(offset.Y, extent.Height - viewport.Height));
// In case last item is visible because we scroll all the way to the right and scrolling is on
// we want desired size not to be smaller than constraint to avoid another relayout
if (logicalExtent > logicalViewport && !Double.IsPositiveInfinity(constraint.Width))
{
stackDesiredSize.Width = constraint.Width;
}
}
else
{
_scrollData._physicalViewport = viewport.Height;
viewport.Height = logicalViewport;
offset.Y = firstViewport;
offset.X = Math.Max(0, Math.Min(offset.X, extent.Width - viewport.Width));
// In case last item is visible because we scroll all the way to the bottom and scrolling is on
// we want desired size not to be smaller than constraint to avoid another relayout
if (logicalExtent > logicalViewport && !Double.IsPositiveInfinity(constraint.Height))
{
stackDesiredSize.Height = constraint.Height;
}
}
// Since we can offset and clip our content, we never need to be larger than the parent suggestion.
// If we returned the full size of the content, we would always be so big we didn't need to scroll. :)
stackDesiredSize.Width = Math.Min(stackDesiredSize.Width, constraint.Width);
stackDesiredSize.Height = Math.Min(stackDesiredSize.Height, constraint.Height);
// When scrolling, the maximum horizontal or vertical size of items can cause the desired size of the
// panel to change, which can cause the owning ScrollViewer re-layout as well when it is not necessary.
// We will thus remember the maximum desired size and always return that. The actual arrangement and
// clipping still be calculated from actual scroll data values.
// The maximum desired size is reset when the items change.
_scrollData._maxDesiredSize.Width = Math.Max(stackDesiredSize.Width, _scrollData._maxDesiredSize.Width);
_scrollData._maxDesiredSize.Height = Math.Max(stackDesiredSize.Height, _scrollData._maxDesiredSize.Height);
stackDesiredSize = _scrollData._maxDesiredSize;
// Verify Scroll Info, invalidate ScrollOwner if necessary.
VerifyScrollingData(viewport, extent, offset);
}
if (isVirtualizing)
{
EnsureCleanupOperation(false /* delay */);
}
if (etwTracingEnabled)
{
EventTrace.EventProvider.TraceEvent(EventTrace.GuidFromId(EventTraceGuidId.GENERICSTRINGGUID), MS.Utility.EventType.EndEvent, "VirtualizingStackPanel :MeasureOverride");
}
return stackDesiredSize;
}
private void EnsureCleanupOperation(bool delay)
{
if (delay)
{
bool noPendingOperations = true;
if (_cleanupOperation != null)
{
noPendingOperations = _cleanupOperation.Abort();
if (noPendingOperations)
{
_cleanupOperation = null;
}
}
if (noPendingOperations && (_cleanupDelay == null))
{
_cleanupDelay = new DispatcherTimer();
_cleanupDelay.Tick += new EventHandler(OnDelayCleanup);
_cleanupDelay.Interval = TimeSpan.FromMilliseconds(500.0);
_cleanupDelay.Start();
}
}
else
{
if ((_cleanupOperation == null) && (_cleanupDelay == null))
{
_cleanupOperation = Dispatcher.BeginInvoke(DispatcherPriority.Background, new DispatcherOperationCallback(OnCleanUp), null);
}
}
}
private bool PreviousChildIsGenerated(int childIndex)
{
GeneratorPosition position = new GeneratorPosition(childIndex, 0);
position = Generator.GeneratorPositionFromIndex(Generator.IndexFromGeneratorPosition(position) - 1);
return (position.Offset == 0 && position.Index >= 0);
}
private UIElement GeneratePreviousChild(int childIndex, Size layoutSlotSize)
{
int newIndex = Generator.IndexFromGeneratorPosition(new GeneratorPosition(childIndex, 0)) - 1;
if (newIndex >= 0)
{
UIElement child;
IItemContainerGenerator generator = Generator;
ItemsControl itemsControl = ItemsControl.GetItemsOwner(this);
UIElementCollection children = InternalChildren;
int newGeneratedIndex;
GeneratorPosition newStartPos = IndexToGeneratorPositionForStart(newIndex, out newGeneratedIndex);
using (generator.StartAt(newStartPos, GeneratorDirection.Forward, true))
{
bool newlyRealized;
child = generator.GenerateNext(out newlyRealized) as UIElement;
Debug.Assert(child != null, "Null child was generated");
Debug.Assert(newlyRealized, "New child should have been realized");
VirtualizingPanel.InsertInternalChild(children, childIndex, child);
generator.PrepareItemContainer(child);
if (childIndex <= _firstVisibleChildIndex)
{
_firstVisibleChildIndex++;
}
child.Measure(layoutSlotSize);
}
return child;
}
return null;
}
///
/// Called when the Items collection associated with the containing ItemsControl changes.
///
/// sender
/// Event arguments
protected override void OnItemsChanged(object sender, ItemsChangedEventArgs args)
{
base.OnItemsChanged(sender, args);
bool resetMaximumDesiredSize = false;
switch (args.Action)
{
case NotifyCollectionChangedAction.Remove:
OnItemsRemove(args);
resetMaximumDesiredSize = true;
break;
case NotifyCollectionChangedAction.Replace:
OnItemsReplace(args);
resetMaximumDesiredSize = true;
break;
case NotifyCollectionChangedAction.Move:
OnItemsMove(args);
break;
case NotifyCollectionChangedAction.Reset:
resetMaximumDesiredSize = true;
break;
}
if (resetMaximumDesiredSize && IsScrolling)
{
// The items changed such that the maximum size may no longer be valid.
// The next layout pass will update this value.
_scrollData._maxDesiredSize = new Size();
}
}
///
/// Called when the UI collection of children is cleared by the base Panel class.
///
protected override void OnClearChildren()
{
base.OnClearChildren();
_visibleStart = _firstVisibleChildIndex = _visibleCount = 0;
}
private void OnItemsRemove(ItemsChangedEventArgs args)
{
RemoveChildRange(args.Position, args.ItemCount, args.ItemUICount);
}
private void OnItemsReplace(ItemsChangedEventArgs args)
{
RemoveChildRange(args.Position, args.ItemCount, args.ItemUICount);
}
private void OnItemsMove(ItemsChangedEventArgs args)
{
RemoveChildRange(args.OldPosition, args.ItemCount, args.ItemUICount);
}
private void RemoveChildRange(GeneratorPosition position, int itemCount, int itemUICount)
{
UIElementCollection children = InternalChildren;
int pos = position.Index;
if (position.Offset > 0)
{
// An item is being removed after the one at the index
pos++;
}
if (pos < GetGeneratedCount(children))
{
int uiCount = itemUICount;
Debug.Assert((itemCount == itemUICount) || (itemUICount == 0), "Both ItemUICount and ItemCount should be equal or ItemUICount should be 0.");
if (uiCount > 0)
{
VirtualizingPanel.RemoveInternalChildRange(children, pos, uiCount);
}
}
}
private GeneratorPosition IndexToGeneratorPositionForStart(int index, out int childIndex)
{
IItemContainerGenerator generator = Generator;
GeneratorPosition position = (generator != null) ? generator.GeneratorPositionFromIndex(index) : new GeneratorPosition(-1, index + 1);
// determine the position in the children collection for the first
// generated container. This assumes that generator.StartAt will be called
// with direction=Forward and allowStartAtRealizedItem=true.
childIndex = (position.Offset == 0) ? position.Index : position.Index + 1;
return position;
}
private void OnDelayCleanup(object sender, EventArgs e)
{
Debug.Assert(_cleanupDelay != null);
bool needsMoreCleanup = false;
try
{
needsMoreCleanup = CleanUp();
}
finally
{
// Cleanup the timer if more cleanup is unnecessary
if (!needsMoreCleanup)
{
_cleanupDelay.Stop();
_cleanupDelay = null;
}
}
}
private object OnCleanUp(object args)
{
Debug.Assert(_cleanupOperation != null);
bool needsMoreCleanup = false;
try
{
needsMoreCleanup = CleanUp();
}
finally
{
// Keeping this non-null until here in case cleaning up causes re-entrancy
_cleanupOperation = null;
}
if (needsMoreCleanup)
{
EnsureCleanupOperation(true /* delay */);
}
return null;
}
private bool CleanUp()
{
ItemsControl itemsControl = ItemsControl.GetItemsOwner(this);
if ((itemsControl != null) && !GetIsVirtualizing(itemsControl))
{
// Virtualization is turned off, no need to cleanup.
return false;
}
int startMilliseconds = Environment.TickCount;
bool needsMoreCleanup = false;
UIElementCollection children = InternalChildren;
int minDesiredGenerated = MinDesiredGenerated;
int maxDesiredGenerated = MaxDesiredGenerated;
int pageSize = maxDesiredGenerated - minDesiredGenerated;
int extraChildren = GetGeneratedCount(children) - pageSize;
if (extraChildren > (pageSize * 2))
{
if ((Mouse.LeftButton == MouseButtonState.Pressed) &&
(extraChildren < 1000))
{
// An optimization for when we are dragging the mouse.
needsMoreCleanup = true;
}
else
{
bool trailingFocus = IsKeyboardFocusWithin;
bool keepForwardTrail = false;
int focusIndex = -1;
IItemContainerGenerator generator = Generator;
int cleanupRangeStart = 0;
int cleanupCount = 0;
int lastGeneratedIndex = -1;
int counterAdjust;
for (int i = 0; i < GetGeneratedCount(children); i++)
{
// It is possible for TickCount to wrap around about every 30 days.
// If that were to occur, then this particular cleanup may not be interrupted.
// That is OK since the worst that can happen is that there is more of a stutter than normal.
int totalMilliseconds = Environment.TickCount - startMilliseconds;
if ((totalMilliseconds > 50) && (cleanupCount > 0))
{
// Cleanup has been working for 50ms already and the user might start
// noticing a lag. Stop cleaning up and release the thread for other work.
// Cleanup will continue later.
// Don't break out until after at least one item has been found to cleanup.
// Otherwise, we might end up in an infinite loop.
needsMoreCleanup = true;
break;
}
int childIndex = i;
if (trailingFocus)
{
// Focus lies somewhere within the panel, but it has not been found yet.
UIElement child = children[i];
if (child.IsKeyboardFocusWithin)
{
// Focus has been found, we can now re-virtualize items before the focus.
trailingFocus = false;
keepForwardTrail = true;
focusIndex = i;
if (i > 0)
{
// Go through the trailing items and find a focusable item to keep.
int trailIndex = i - 1;
int end = Math.Max(0, i - FocusTrail);
for (; trailIndex >= end; trailIndex--)
{
child = children[trailIndex];
if (Keyboard.IsFocusable(child))
{
trailIndex--;
break;
}
}
// The rest of the trailing items can be re-virtualized.
for (childIndex = end; childIndex <= trailIndex; childIndex++)
{
ManageCleanup(
children,
itemsControl,
generator,
childIndex,
minDesiredGenerated,
maxDesiredGenerated,
ref childIndex,
ref cleanupRangeStart,
ref cleanupCount,
ref lastGeneratedIndex,
out counterAdjust);
if (counterAdjust > 0)
{
i -= counterAdjust;
trailIndex -= counterAdjust;
}
}
if (cleanupCount > 0)
{
// Cleanup the last batch for the focused item
CleanupRange(children, generator, cleanupRangeStart, cleanupCount);
i -= cleanupCount;
cleanupCount = 0;
}
cleanupRangeStart = i + 1;
// At this point, we are caught up and should go to the next item
continue;
}
}
else if (i >= FocusTrail)
{
childIndex = i - FocusTrail;
}
else
{
continue;
}
}
if (keepForwardTrail)
{
// Find a focusable item after the focused item to keep
if (childIndex <= (focusIndex + FocusTrail))
{
UIElement child = children[childIndex];
if (Keyboard.IsFocusable(child))
{
// A focusable item was found, all items after this one can be re-virtualized
keepForwardTrail = false;
cleanupRangeStart = childIndex + 1;
cleanupCount = 0;
}
continue;
}
else
{
keepForwardTrail = false;
}
}
ManageCleanup(
children,
itemsControl,
generator,
childIndex,
minDesiredGenerated,
maxDesiredGenerated,
ref i,
ref cleanupRangeStart,
ref cleanupCount,
ref lastGeneratedIndex,
out counterAdjust);
}
if (cleanupCount > 0)
{
// Cleanup the final batch
CleanupRange(children, generator, cleanupRangeStart, cleanupCount);
}
}
}
return needsMoreCleanup;
}
private void ManageCleanup(
UIElementCollection children,
ItemsControl itemsControl,
IItemContainerGenerator generator,
int childIndex,
int minDesiredGenerated,
int maxDesiredGenerated,
ref int counter,
ref int cleanupRangeStart,
ref int cleanupCount,
ref int lastGeneratedIndex,
out int counterAdjust)
{
counterAdjust = 0;
bool performCleanup = false;
bool countThisChild = false;
int generatedIndex = GetGeneratedIndex(childIndex);
if (OutsideMinMax(generatedIndex, minDesiredGenerated, maxDesiredGenerated) &&
NotifyCleanupItem(childIndex, children, itemsControl, generator))
{
// The item can be re-virtualized.
if ((generatedIndex - lastGeneratedIndex) == 1)
{
// Add another to the current batch.
cleanupCount++;
}
else
{
// There was a gap in generated items. Cleanup any from the previous batch.
performCleanup = countThisChild = true;
}
}
else
{
// The item cannot be re-virtualized. Cleanup any from the previous batch.
performCleanup = true;
}
if (performCleanup)
{
// Cleanup a batch of items
if (cleanupCount > 0)
{
CleanupRange(children, generator, cleanupRangeStart, cleanupCount);
counterAdjust = cleanupCount;
counter -= counterAdjust;
childIndex -= counterAdjust;
cleanupCount = 0;
}
if (countThisChild)
{
// The current child was not included in the batch and should be saved for later
cleanupRangeStart = childIndex;
cleanupCount = 1;
}
else
{
// The next child will start the next batch.
cleanupRangeStart = childIndex + 1;
}
}
lastGeneratedIndex = generatedIndex;
}
private bool NotifyCleanupItem(int childIndex, UIElementCollection children, ItemsControl itemsControl, IItemContainerGenerator generator)
{
UIElement child = children[childIndex];
CleanUpVirtualizedItemEventArgs e = new CleanUpVirtualizedItemEventArgs(itemsControl.ItemContainerGenerator.ItemFromContainer(child), child);
e.Source = this;
OnCleanUpVirtualizedItem(e);
return !e.Cancel;
}
private void CleanupRange(UIElementCollection children, IItemContainerGenerator generator, int startIndex, int count)
{
// Remove the desired range of children
VirtualizingPanel.RemoveInternalChildRange(children, startIndex, count);
generator.Remove(new GeneratorPosition(startIndex, 0), count);
// Update the index of the first visible generated child
if (startIndex < _firstVisibleChildIndex)
{
int endIndex = startIndex + count - 1;
if (endIndex < _firstVisibleChildIndex)
{
// The first visible index is after the items that were removed
_firstVisibleChildIndex -= count;
}
else
{
// The first visible index was within the items that were removed
_firstVisibleChildIndex = startIndex;
}
}
}
private static bool OutsideMinMax(int i, int min, int max)
{
return ((i < min) || (i > max));
}
private void EnsureTopCapGenerated(Size layoutSlotSize)
{
// Ensure that a focusable item is generated above the first visible item
// so that keyboard navigation works.
_beforeTrail = 0;
if (_visibleStart > 0)
{
int childIndex = _firstVisibleChildIndex;
UIElementCollection children = InternalChildren;
UIElement child;
// At most, we will search FocusTrail number of items for a focusable item
for (; _beforeTrail < FocusTrail; _beforeTrail++)
{
if (PreviousChildIsGenerated(childIndex))
{
// The previous child is already generated, check its focusability
childIndex--;
child = children[childIndex];
}
else
{
// Generate the previous child
child = GeneratePreviousChild(childIndex, layoutSlotSize);
}
if ((child == null) || Keyboard.IsFocusable(child))
{
// Either a focusable item was found, or no child was generated
_beforeTrail++;
break;
}
}
}
}
private int MinDesiredGenerated
{
get
{
return Math.Max(0, _visibleStart - _beforeTrail);
}
}
private int MaxDesiredGenerated
{
get
{
return Math.Min(ItemCount, _visibleStart + _visibleCount + _afterTrail);
}
}
private int ItemCount
{
get
{
ItemsControl itemsControl = ItemsControl.GetItemsOwner(this);
return (itemsControl != null) ? itemsControl.Items.Count : 0;
}
}
///
/// Content arrangement.
///
/// Arrange size
protected override Size ArrangeOverride(Size arrangeSize)
{
ItemsControl itemsControl = ItemsControl.GetItemsOwner(this);
bool isVirtualizing = (itemsControl != null) ? GetIsVirtualizing(itemsControl) : true;
bool fHorizontal = (Orientation == Orientation.Horizontal);
Rect rcChild = new Rect(arrangeSize);
double previousChildSize = 0.0;
bool etwTracingEnabled = IsScrolling && EventTrace.IsEnabled(EventTrace.Flags.performance, EventTrace.Level.normal);
if (etwTracingEnabled)
{
EventTrace.EventProvider.TraceEvent(EventTrace.GuidFromId(EventTraceGuidId.GENERICSTRINGGUID), MS.Utility.EventType.StartEvent, "VirtualizingStackPanel :ArrangeOverride");
}
//
// Compute scroll offset and seed it into rcChild.
//
if (IsScrolling)
{
if (fHorizontal)
{
rcChild.X = ComputePhysicalFromLogicalOffset(isVirtualizing ? _firstVisibleChildIndex : _scrollData._computedOffset.X, true);
rcChild.Y = -1.0 * _scrollData._computedOffset.Y;
}
else
{
rcChild.X = -1.0 * _scrollData._computedOffset.X;
rcChild.Y = ComputePhysicalFromLogicalOffset(isVirtualizing ? _firstVisibleChildIndex : _scrollData._computedOffset.Y, false);
}
}
//
// Arrange and Position Children.
//
int childrenCount = InternalChildren.Count;
for (int i = 0; i < childrenCount; ++i)
{
UIElement child = InternalChildren[i];
if (child != null)
{
if (fHorizontal)
{
rcChild.X += previousChildSize;
previousChildSize = child.DesiredSize.Width;
rcChild.Width = previousChildSize;
rcChild.Height = Math.Max(arrangeSize.Height, child.DesiredSize.Height);
}
else
{
rcChild.Y += previousChildSize;
previousChildSize = child.DesiredSize.Height;
rcChild.Height = previousChildSize;
rcChild.Width = Math.Max(arrangeSize.Width, child.DesiredSize.Width);
}
child.Arrange(rcChild);
}
}
if (etwTracingEnabled)
{
EventTrace.EventProvider.TraceEvent(EventTrace.GuidFromId(EventTraceGuidId.GENERICSTRINGGUID), MS.Utility.EventType.EndEvent, "VirtualizingStackPanel :ArrangeOverride");
}
return arrangeSize;
}
#endregion Protected Methods
//------------------------------------------------------
//
// Private Methods
//
//-----------------------------------------------------
#region Private Methods
private void EnsureScrollData()
{
if (_scrollData == null) { _scrollData = new ScrollData(); }
}
private static void ResetScrolling(VirtualizingStackPanel element)
{
element.InvalidateMeasure();
// Clear scrolling data. Because of thrash (being disconnected & reconnected, &c...), we may
if (element.IsScrolling)
{
element._scrollData.ClearLayout();
}
}
// OnScrollChange is an override called whenever the IScrollInfo exposed scrolling state changes on this element.
// At the time this method is called, scrolling state is in its new, valid state.
private void OnScrollChange()
{
if (ScrollOwner != null) { ScrollOwner.InvalidateScrollInfo(); }
}
private void VerifyScrollingData(Size viewport, Size extent, Vector offset)
{
bool fValid = true;
Debug.Assert(IsScrolling);
fValid &= DoubleUtil.AreClose(viewport, _scrollData._viewport);
fValid &= DoubleUtil.AreClose(extent, _scrollData._extent);
fValid &= DoubleUtil.AreClose(offset, _scrollData._computedOffset);
_scrollData._offset = offset;
if (!fValid)
{
_scrollData._viewport = viewport;
_scrollData._extent = extent;
_scrollData._computedOffset = offset;
OnScrollChange();
}
}
// Translates a logical (child index) offset to a physical (1/96") when scrolling.
// If virtualizing, it makes the assumption that the logicalOffset is always the first in the visual collection
// and thus returns 0.
// If not virtualizing, it assumes that children are Measure clean; should only be called after running Measure.
private double ComputePhysicalFromLogicalOffset(double logicalOffset, bool fHorizontal)
{
double physicalOffset = 0.0;
int childrenCount = InternalChildren.Count;
Debug.Assert(logicalOffset == 0 || (logicalOffset > 0 && logicalOffset < childrenCount));
for (int i = 0; i < logicalOffset; i++)
{
physicalOffset -= (fHorizontal)
? InternalChildren[i].DesiredSize.Width
: InternalChildren[i].DesiredSize.Height;
}
return physicalOffset;
}
private int FindChildIndexThatParentsVisual(Visual v)
{
DependencyObject child = v;
DependencyObject parent = VisualTreeHelper.GetParent(child);
while (parent != this)
{
child = parent;
parent = VisualTreeHelper.GetParent(child);
}
UIElementCollection children = InternalChildren;
for (int i = 0; i < children.Count; i++)
{
if (children[i] == child)
{
return GetGeneratedIndex(i);
}
}
return -1;
}
private void MakeVisiblePhysicalHelper(Rect r, ref Vector newOffset, ref Rect newRect)
{
double viewportOffset;
double viewportSize;
double targetRectOffset;
double targetRectSize;
double minPhysicalOffset;
bool fHorizontal = (Orientation == Orientation.Horizontal);
if (fHorizontal)
{
viewportOffset = _scrollData._computedOffset.Y;
viewportSize = ViewportHeight;
targetRectOffset = r.Y;
targetRectSize = r.Height;
}
else
{
viewportOffset = _scrollData._computedOffset.X;
viewportSize = ViewportWidth;
targetRectOffset = r.X;
targetRectSize = r.Width;
}
targetRectOffset += viewportOffset;
minPhysicalOffset = ScrollContentPresenter.ComputeScrollOffsetWithMinimalScroll(
viewportOffset, viewportOffset + viewportSize, targetRectOffset, targetRectOffset + targetRectSize);
// Compute the visible rectangle of the child relative to the viewport.
double left = Math.Max(targetRectOffset, minPhysicalOffset);
targetRectSize = Math.Max(Math.Min(targetRectSize + targetRectOffset, minPhysicalOffset + viewportSize) - left, 0);
targetRectOffset = left;
targetRectOffset -= viewportOffset;
if (fHorizontal)
{
newOffset.Y = minPhysicalOffset;
newRect.Y = targetRectOffset;
newRect.Height = targetRectSize;
}
else
{
newOffset.X = minPhysicalOffset;
newRect.X = targetRectOffset;
newRect.Width = targetRectSize;
}
}
private void MakeVisibleLogicalHelper(int childIndex, Rect r, ref Vector newOffset, ref Rect newRect)
{
bool fHorizontal = (Orientation == Orientation.Horizontal);
int firstChildInView;
int newFirstChild;
int viewportSize;
double childOffsetWithinViewport = r.Y;
if (fHorizontal)
{
firstChildInView = (int)_scrollData._computedOffset.X;
viewportSize = (int)_scrollData._viewport.Width;
}
else
{
firstChildInView = (int)_scrollData._computedOffset.Y;
viewportSize = (int)_scrollData._viewport.Height;
}
newFirstChild = firstChildInView;
// If the target child is before the current viewport, move the viewport to put the child at the top.
if (childIndex < firstChildInView)
{
childOffsetWithinViewport = 0;
newFirstChild = childIndex;
}
// If the target child is after the current viewport, move the viewport to put the child at the bottom.
else if (childIndex > firstChildInView + viewportSize - 1)
{
newFirstChild = childIndex - viewportSize + 1;
double pixelSize = fHorizontal ? ActualWidth : ActualHeight;
childOffsetWithinViewport = pixelSize * (1.0 - (1.0 / viewportSize));
}
if (fHorizontal)
{
newOffset.X = newFirstChild;
newRect.X = childOffsetWithinViewport;
newRect.Width = r.Width;
}
else
{
newOffset.Y = newFirstChild;
newRect.Y = childOffsetWithinViewport;
newRect.Height = r.Height;
}
}
static private int CoerceOffsetToInteger(double offset, int numberOfItems)
{
int iNewOffset;
if (Double.IsNegativeInfinity(offset))
{
iNewOffset = 0;
}
else if (Double.IsPositiveInfinity(offset))
{
iNewOffset = numberOfItems - 1;
}
else
{
iNewOffset = (int)offset;
iNewOffset = Math.Max(Math.Min(numberOfItems - 1, iNewOffset), 0);
}
return iNewOffset;
}
private int GetGeneratedCount(UIElementCollection children)
{
return IsItemsHost ? children.Count : 0;
}
private int GetGeneratedIndex(int childIndex)
{
return Generator.IndexFromGeneratorPosition(new GeneratorPosition(childIndex, 0));
}
//------------------------------------------------------------
// Avalon Property Callbacks/Overrides
//-----------------------------------------------------------
#region Avalon Property Callbacks/Overrides
///
///
private static void OnOrientationChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
// Since Orientation is so essential to logical scrolling/virtualization, we synchronously check if
// the new value is different and clear all scrolling data if so.
ResetScrolling(d as VirtualizingStackPanel);
}
#endregion
#endregion Private Methods
//-----------------------------------------------------
//
// Private Properties
//
//-----------------------------------------------------
#region Private Properties
private bool IsScrolling
{
get { return (_scrollData != null) && (_scrollData._scrollOwner != null); }
}
#endregion Private Properties
//------------------------------------------------------
//
// Private Fields
//
//-----------------------------------------------------
#region Private Fields
// Logical scrolling and virtualization data.
private ScrollData _scrollData;
// Virtualization state
private int _visibleStart;
private int _visibleCount;
private int _firstVisibleChildIndex;
// Cleanup
private DispatcherOperation _cleanupOperation;
private DispatcherTimer _cleanupDelay;
private int _beforeTrail = 0;
private int _afterTrail = 0;
private const int FocusTrail = 5; // The maximum number of items off the edge we will generate to get a focused item (so that keyboard navigation can work)
#endregion Private Fields
//------------------------------------------------------
//
// Private Structures / Classes
//
//------------------------------------------------------
#region Private Structures Classes
//-----------------------------------------------------------
// ScrollData class
//------------------------------------------------------------
#region ScrollData
// Helper class to hold scrolling data.
// This class exists to reduce working set when VirtualizingStackPanel is used outside a scrolling situation.
// Standard "extra pointer always for less data sometimes" cache savings model:
// !Scroll [1xReference]
// Scroll [1xReference] + [6xDouble + 1xReference]
private class ScrollData
{
// Clears layout generated data.
// Does not clear scrollOwner, because unless resetting due to a scrollOwner change, we won't get reattached.
internal void ClearLayout()
{
_offset = new Vector();
_viewport = _extent = _maxDesiredSize = new Size();
_physicalViewport = 0;
}
// For Stack/Flow, the two dimensions of properties are in different units:
// 1. The "logically scrolling" dimension uses items as units.
// 2. The other dimension physically scrolls. Units are in Avalon pixels (1/96").
internal bool _allowHorizontal;
internal bool _allowVertical;
internal Vector _offset; // Scroll offset of content. Positive corresponds to a visually upward offset.
internal Vector _computedOffset = new Vector(0,0);
internal Size _viewport; // ViewportSize is in {pixels x items} (or vice-versa).
internal Size _extent; // Extent is the total number of children (logical dimension) or physical size
internal double _physicalViewport; // The physical size of the viewport for the items dimension above.
internal ScrollViewer _scrollOwner; // ScrollViewer to which we're attached.
internal Size _maxDesiredSize; // Hold onto the maximum desired size to avoid re-laying out the parent ScrollViewer.
}
#endregion ScrollData
#endregion Private Structures Classes
}
}
// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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