public Size Measure(
Size availableSize,
VirtualizingLayoutContext context,
bool isWrapping,
double minItemSpacing,
double lineSpacing,
uint maxItemsPerLine,
ScrollOrientation orientation,
bool disableVirtualization,
string layoutId)
{
OM.ScrollOrientation = orientation;
// If minor size is infinity, there is only one line and no need to align that line.
m_scrollOrientationSameAsFlow = double.IsInfinity(OM.Minor(availableSize));
var suggestedAnchorIndex = m_context.RecommendedAnchorIndex;
if (m_elementManager.IsIndexValidInData(suggestedAnchorIndex))
{
var anchorRealized = m_elementManager.IsDataIndexRealized(suggestedAnchorIndex);
if (!anchorRealized)
{
MakeAnchor(m_context, suggestedAnchorIndex, availableSize);
}
}
m_elementManager.OnBeginMeasure(orientation);
int anchorIndex = GetAnchorIndex(availableSize, isWrapping, minItemSpacing, layoutId);
Generate(GenerateDirection.Forward, anchorIndex, availableSize, minItemSpacing, lineSpacing, maxItemsPerLine, disableVirtualization, layoutId);
Generate(GenerateDirection.Backward, anchorIndex, availableSize, minItemSpacing, lineSpacing, maxItemsPerLine, disableVirtualization, layoutId);
if (isWrapping && IsReflowRequired)
{
var firstElementBounds = m_elementManager.GetLayoutBoundsForRealizedIndex(0);
OM.SetMinorStart(ref firstElementBounds, 0);
m_elementManager.SetLayoutBoundsForRealizedIndex(0, firstElementBounds);
Generate(GenerateDirection.Forward, 0 /*anchorIndex*/, availableSize, minItemSpacing, lineSpacing, maxItemsPerLine, disableVirtualization, layoutId);
}
RaiseLineArranged();
m_collectionChangePending = false;
m_lastExtent = EstimateExtent(availableSize, layoutId);
SetLayoutOrigin();
return(new Size(m_lastExtent.Width, m_lastExtent.Height));
}
private void ArrangeVirtualizingLayout(
Size finalSize,
LineAlignment lineAlignment,
bool isWrapping,
string layoutId)
{
// Walk through the realized elements one line at a time and
// align them, Then call element.Arrange with the arranged bounds.
int realizedElementCount = m_elementManager.GetRealizedElementCount();
if (realizedElementCount > 0)
{
int countInLine = 1;
var previousElementBounds = m_elementManager.GetLayoutBoundsForRealizedIndex(0);
var currentLineOffset = OM.MajorStart(previousElementBounds);
var spaceAtLineStart = OM.MinorStart(previousElementBounds);
double spaceAtLineEnd = 0;
double currentLineSize = OM.MajorSize(previousElementBounds);
for (int i = 1; i < realizedElementCount; i++)
{
var currentBounds = m_elementManager.GetLayoutBoundsForRealizedIndex(i);
if (OM.MajorStart(currentBounds) != currentLineOffset)
{
spaceAtLineEnd = OM.Minor(finalSize) - OM.MinorStart(previousElementBounds) - OM.MinorSize(previousElementBounds);
PerformLineAlignment(i - countInLine, countInLine, spaceAtLineStart, spaceAtLineEnd, currentLineSize, lineAlignment, isWrapping, finalSize, layoutId);
spaceAtLineStart = OM.MinorStart(currentBounds);
countInLine = 0;
currentLineOffset = OM.MajorStart(currentBounds);
currentLineSize = 0;
}
countInLine++; // for current element
currentLineSize = Math.Max(currentLineSize, OM.MajorSize(currentBounds));
previousElementBounds = currentBounds;
}
// Last line - potentially have a property to customize
// aligning the last line or not.
if (countInLine > 0)
{
double spaceAtEnd = OM.Minor(finalSize) - OM.MinorStart(previousElementBounds) - OM.MinorSize(previousElementBounds);
PerformLineAlignment(realizedElementCount - countInLine, countInLine, spaceAtLineStart, spaceAtEnd, currentLineSize, lineAlignment, isWrapping, finalSize, layoutId);
}
}
}
// Align elements within a line. Note that this does not modify LayoutBounds. So if we get
// repeated measures, the LayoutBounds remain the same in each layout.
private void PerformLineAlignment(
int lineStartIndex,
int countInLine,
double spaceAtLineStart,
double spaceAtLineEnd,
double lineSize,
LineAlignment lineAlignment,
bool isWrapping,
Size finalSize,
string layoutId)
{
for (int rangeIndex = lineStartIndex; rangeIndex < lineStartIndex + countInLine; ++rangeIndex)
{
var bounds = m_elementManager.GetLayoutBoundsForRealizedIndex(rangeIndex);
OM.SetMajorSize(ref bounds, lineSize);
if (!m_scrollOrientationSameAsFlow)
{
// Note: Space at start could potentially be negative
if (spaceAtLineStart != 0 || spaceAtLineEnd != 0)
{
double totalSpace = spaceAtLineStart + spaceAtLineEnd;
switch (lineAlignment)
{
case LineAlignment.Start:
{
OM.SetMinorStart(ref bounds, OM.MinorStart(bounds) - spaceAtLineStart);
break;
}
case LineAlignment.End:
{
OM.SetMinorStart(ref bounds, OM.MinorStart(bounds) + spaceAtLineEnd);
break;
}
case LineAlignment.Center:
{
OM.SetMinorStart(ref bounds, OM.MinorStart(bounds) - spaceAtLineStart);
OM.SetMinorStart(ref bounds, OM.MinorStart(bounds) + totalSpace / 2);
break;
}
case LineAlignment.SpaceAround:
{
double interItemSpace = countInLine >= 1 ? totalSpace / (countInLine * 2) : 0;
OM.SetMinorStart(ref bounds, OM.MinorStart(bounds) - spaceAtLineStart);
OM.SetMinorStart(ref bounds, OM.MinorStart(bounds) + interItemSpace * ((rangeIndex - lineStartIndex + 1) * 2 - 1));
break;
}
case LineAlignment.SpaceBetween:
{
double interItemSpace = countInLine > 1 ? totalSpace / (countInLine - 1) : 0;
OM.SetMinorStart(ref bounds, OM.MinorStart(bounds) - spaceAtLineStart);
OM.SetMinorStart(ref bounds, OM.MinorStart(bounds) + interItemSpace * (rangeIndex - lineStartIndex));
break;
}
case LineAlignment.SpaceEvenly:
{
double interItemSpace = countInLine >= 1 ? totalSpace / (countInLine + 1) : 0;
OM.SetMinorStart(ref bounds, OM.MinorStart(bounds) - spaceAtLineStart);
OM.SetMinorStart(ref bounds, OM.MinorStart(bounds) + interItemSpace * (rangeIndex - lineStartIndex + 1));
break;
}
}
}
}
bounds.X -= m_lastExtent.X;
bounds.Y -= m_lastExtent.Y;
if (!isWrapping)
{
OM.SetMinorSize(ref bounds, Math.Max(OM.MinorSize(bounds), OM.Minor(finalSize)));
}
var element = m_elementManager.GetAt(rangeIndex);
element.Arrange(bounds);
}
}
private void Generate(
GenerateDirection direction,
int anchorIndex,
Size availableSize,
double minItemSpacing,
double lineSpacing,
uint maxItemsPerLine,
bool disableVirtualization,
string layoutId)
{
if (anchorIndex != -1)
{
int step = (direction == GenerateDirection.Forward) ? 1 : -1;
int previousIndex = anchorIndex;
int currentIndex = anchorIndex + step;
var anchorBounds = m_elementManager.GetLayoutBoundsForDataIndex(anchorIndex);
double lineOffset = OM.MajorStart(anchorBounds);
double lineMajorSize = OM.MajorSize(anchorBounds);
uint countInLine = 1;
bool lineNeedsReposition = false;
while (m_elementManager.IsIndexValidInData(currentIndex) &&
(disableVirtualization || ShouldContinueFillingUpSpace(previousIndex, direction)))
{
// Ensure layout element.
m_elementManager.EnsureElementRealized(direction == GenerateDirection.Forward, currentIndex, layoutId);
var currentElement = m_elementManager.GetRealizedElement(currentIndex);
var desiredSize = MeasureElement(currentElement, currentIndex, availableSize, m_context);
// Lay it out.
var previousElement = m_elementManager.GetRealizedElement(previousIndex);
Rect currentBounds = new Rect(0, 0, desiredSize.Width, desiredSize.Height);
var previousElementBounds = m_elementManager.GetLayoutBoundsForDataIndex(previousIndex);
if (direction == GenerateDirection.Forward)
{
double remainingSpace = OM.Minor(availableSize) - (OM.MinorStart(previousElementBounds) + OM.MinorSize(previousElementBounds) + minItemSpacing + OM.Minor(desiredSize));
if (countInLine >= maxItemsPerLine || m_algorithmCallbacks.Algorithm_ShouldBreakLine(currentIndex, remainingSpace))
{
// No more space in this row. wrap to next row.
OM.SetMinorStart(ref currentBounds, 0);
OM.SetMajorStart(ref currentBounds, OM.MajorStart(previousElementBounds) + lineMajorSize + lineSpacing);
if (lineNeedsReposition)
{
// reposition the previous line (countInLine items)
for (uint i = 0; i < countInLine; i++)
{
var dataIndex = currentIndex - 1 - i;
var bounds = m_elementManager.GetLayoutBoundsForDataIndex((int)dataIndex);
OM.SetMajorSize(ref bounds, lineMajorSize);
m_elementManager.SetLayoutBoundsForDataIndex((int)dataIndex, bounds);
}
}
// Setup for next line.
lineMajorSize = OM.MajorSize(currentBounds);
lineOffset = OM.MajorStart(currentBounds);
lineNeedsReposition = false;
countInLine = 1;
}
else
{
// More space is available in this row.
OM.SetMinorStart(ref currentBounds, OM.MinorStart(previousElementBounds) + OM.MinorSize(previousElementBounds) + (minItemSpacing));
OM.SetMajorStart(ref currentBounds, lineOffset);
lineMajorSize = Math.Max(lineMajorSize, OM.MajorSize(currentBounds));
lineNeedsReposition = OM.MajorSize(previousElementBounds) != OM.MajorSize(currentBounds);
countInLine++;
}
}
else
{
// Backward
double remainingSpace = OM.MinorStart(previousElementBounds) - (OM.Minor(desiredSize) + minItemSpacing);
if (countInLine >= maxItemsPerLine || m_algorithmCallbacks.Algorithm_ShouldBreakLine(currentIndex, remainingSpace))
{
// Does not fit, wrap to the previous row
var availableSizeMinor = OM.Minor(availableSize);
OM.SetMinorStart(ref currentBounds, !double.IsInfinity(availableSizeMinor) ? availableSizeMinor - OM.Minor(desiredSize) : 0.0);
OM.SetMajorStart(ref currentBounds, lineOffset - OM.Major(desiredSize) - lineSpacing);
if (lineNeedsReposition)
{
var previousLineOffset = OM.MajorStart(m_elementManager.GetLayoutBoundsForDataIndex((int)(currentIndex + countInLine + 1)));
// reposition the previous line (countInLine items)
for (uint i = 0; i < countInLine; i++)
{
var dataIndex = currentIndex + 1 + (int)i;
if (dataIndex != anchorIndex)
{
var bounds = m_elementManager.GetLayoutBoundsForDataIndex(dataIndex);
OM.SetMajorStart(ref bounds, previousLineOffset - lineMajorSize - lineSpacing);
OM.SetMajorSize(ref bounds, lineMajorSize);
m_elementManager.SetLayoutBoundsForDataIndex(dataIndex, bounds);
}
}
}
// Setup for next line.
lineMajorSize = OM.MajorSize(currentBounds);
lineOffset = OM.MajorStart(currentBounds);
lineNeedsReposition = false;
countInLine = 1;
}
else
{
// Fits in this row. put it in the previous position
OM.SetMinorStart(ref currentBounds, OM.MinorStart(previousElementBounds) - OM.Minor(desiredSize) - minItemSpacing);
OM.SetMajorStart(ref currentBounds, lineOffset);
lineMajorSize = Math.Max(lineMajorSize, OM.MajorSize(currentBounds));
lineNeedsReposition = OM.MajorSize(previousElementBounds) != OM.MajorSize(currentBounds);
countInLine++;
}
}
m_elementManager.SetLayoutBoundsForDataIndex(currentIndex, currentBounds);
previousIndex = currentIndex;
currentIndex += step;
}
// If we did not reach the top or bottom of the extent, we realized one
// extra item before we knew we were outside the realization window. Do not
// account for that element in the indicies inside the realization window.
if (direction == GenerateDirection.Forward)
{
int dataCount = m_context.ItemCount;
m_lastRealizedDataIndexInsideRealizationWindow = previousIndex == dataCount - 1 ? dataCount - 1 : previousIndex - 1;
m_lastRealizedDataIndexInsideRealizationWindow = Math.Max(0, m_lastRealizedDataIndexInsideRealizationWindow);
}
else
{
int dataCount = m_context.ItemCount;
m_firstRealizedDataIndexInsideRealizationWindow = previousIndex == 0 ? 0 : previousIndex + 1;
m_firstRealizedDataIndexInsideRealizationWindow = Math.Min(dataCount - 1, m_firstRealizedDataIndexInsideRealizationWindow);
}
m_elementManager.DiscardElementsOutsideWindow(direction == GenerateDirection.Forward, currentIndex);
}
}
private int GetAnchorIndex(
Size availableSize,
bool isWrapping,
double minItemSpacing,
string layoutId)
{
int anchorIndex = -1;
Point anchorPosition = default;
if (!IsVirtualizingContext)
{
// Non virtualizing host, start generating from the element 0
anchorIndex = ((IVirtualizingLayoutContextOverrides)m_context).ItemCountCore() > 0 ? 0 : -1;
}
else
{
bool isRealizationWindowConnected = m_elementManager.IsWindowConnected(RealizationRect, OM.ScrollOrientation, m_scrollOrientationSameAsFlow);
// Item spacing and size in non-virtualizing direction change can cause elements to reflow
// and get a new column position. In that case we need the anchor to be positioned in the
// correct column.
bool needAnchorColumnRevaluation = isWrapping && (
OM.Minor(m_lastAvailableSize) != OM.Minor(availableSize) ||
m_lastItemSpacing != minItemSpacing ||
m_collectionChangePending);
var suggestedAnchorIndex = m_context.RecommendedAnchorIndex;
bool isAnchorSuggestionValid = suggestedAnchorIndex >= 0 &&
m_elementManager.IsDataIndexRealized(suggestedAnchorIndex);
if (isAnchorSuggestionValid)
{
anchorIndex = m_algorithmCallbacks.Algorithm_GetAnchorForTargetElement(
suggestedAnchorIndex,
availableSize,
m_context).Index;
if (m_elementManager.IsDataIndexRealized(anchorIndex))
{
var anchorBounds = m_elementManager.GetLayoutBoundsForDataIndex(anchorIndex);
if (needAnchorColumnRevaluation)
{
// We were provided a valid anchor, but its position might be incorrect because for example it is in
// the wrong column. We do know that the anchor is the first element in the row, so we can force the minor position
// to start at 0.
anchorPosition = OM.MinorMajorPoint(0, OM.MajorStart(anchorBounds));
}
else
{
anchorPosition = new Point(anchorBounds.X, anchorBounds.Y);
}
}
else
{
// It is possible to end up in a situation during a collection change where GetAnchorForTargetElement returns an index
// which is not in the realized range. Eg. insert one item at index 0 for a grid layout.
// SuggestedAnchor will be 1 (used to be 0) and GetAnchorForTargetElement will return 0 (left most item in row). However 0 is not in the
// realized range yet. In this case we realize the gap between the target anchor and the suggested anchor.
int firstRealizedDataIndex = m_elementManager.GetDataIndexFromRealizedRangeIndex(0);
Debug.Assert(anchorIndex < firstRealizedDataIndex);
for (int i = firstRealizedDataIndex - 1; i >= anchorIndex; --i)
{
m_elementManager.EnsureElementRealized(false /*forward*/, i, layoutId);
}
var anchorBounds = m_elementManager.GetLayoutBoundsForDataIndex(suggestedAnchorIndex);
anchorPosition = OM.MinorMajorPoint(0, OM.MajorStart(anchorBounds));
}
}
else if (needAnchorColumnRevaluation || !isRealizationWindowConnected)
{
// The anchor is based on the realization window because a connected ItemsRepeater might intersect the realization window
// but not the visible window. In that situation, we still need to produce a valid anchor.
var anchorInfo = m_algorithmCallbacks.Algorithm_GetAnchorForRealizationRect(availableSize, m_context);
anchorIndex = anchorInfo.Index;
anchorPosition = OM.MinorMajorPoint(0, anchorInfo.Offset);
}
else
{
// No suggestion - just pick first in realized range
anchorIndex = m_elementManager.GetDataIndexFromRealizedRangeIndex(0);
var firstElementBounds = m_elementManager.GetLayoutBoundsForRealizedIndex(0);
anchorPosition = new Point(firstElementBounds.X, firstElementBounds.Y);
}
}
Debug.Assert(anchorIndex == -1 || m_elementManager.IsIndexValidInData(anchorIndex));
m_firstRealizedDataIndexInsideRealizationWindow = m_lastRealizedDataIndexInsideRealizationWindow = anchorIndex;
if (m_elementManager.IsIndexValidInData(anchorIndex))
{
if (!m_elementManager.IsDataIndexRealized(anchorIndex))
{
// Disconnected, throw everything and create new anchor
m_elementManager.ClearRealizedRange();
var anchor = m_context.GetOrCreateElementAt(anchorIndex, ElementRealizationOptions.ForceCreate | ElementRealizationOptions.SuppressAutoRecycle);
m_elementManager.Add(anchor, anchorIndex);
}
var anchorElement = m_elementManager.GetRealizedElement(anchorIndex);
var desiredSize = MeasureElement(anchorElement, anchorIndex, availableSize, m_context);
var layoutBounds = new Rect(anchorPosition.X, anchorPosition.Y, desiredSize.Width, desiredSize.Height);
m_elementManager.SetLayoutBoundsForDataIndex(anchorIndex, layoutBounds);
}
else
{
// Throw everything away
m_elementManager.ClearRealizedRange();
}
// TODO: Perhaps we can track changes in the property setter
m_lastAvailableSize = availableSize;
m_lastItemSpacing = minItemSpacing;
return(anchorIndex);
}
