protected override void ArrangeChildren()
{
bool fireScrolled = false;
lock (Children.SyncRoot)
{
if (ItemProvider == null)
{
base.ArrangeChildren();
return;
}
_totalHeight = 0;
_totalWidth = 0;
int numItems = ItemProvider.NumItems;
if (numItems > 0)
{
PointF actualPosition = ActualPosition;
SizeF actualSize = new SizeF((float)ActualWidth, (float)ActualHeight);
// For Orientation == vertical, this is ActualHeight, for horizontal it is ActualWidth
float actualExtendsInOrientationDirection = GetExtendsInOrientationDirection(Orientation, actualSize);
// For Orientation == vertical, this is ActualWidth, for horizontal it is ActualHeight
float actualExtendsInNonOrientationDirection = GetExtendsInNonOrientationDirection(Orientation, actualSize);
// Hint: We cannot skip the arrangement of lines above _actualFirstVisibleLineIndex or below _actualLastVisibleLineIndex
// because the rendering and focus system also needs the bounds of the currently invisible children
float startPosition = 0;
// If set to true, we'll check available space from the last to first visible child.
// That is necessary if we want to scroll a specific child to the last visible position.
bool invertLayouting = false;
lock (_renderLock)
if (_pendingScrollIndex.HasValue)
{
fireScrolled = true;
int pendingSI = _pendingScrollIndex.Value;
if (_scrollToFirst)
{
_actualFirstVisibleLineIndex = pendingSI;
}
else
{
_actualLastVisibleLineIndex = pendingSI;
invertLayouting = true;
}
_pendingScrollIndex = null;
}
int itemsPerLine = 0;
// if we haven't arranged any lines previously - items per line can't be calculated yet, but is not needed
if (_firstArrangedLineIndex >= 0)
{
// to calculate the starting index of elements for a line we assume that every line (until the last) has the same number of items
itemsPerLine = _arrangedLines[_firstArrangedLineIndex].EndIndex - _arrangedLines[_firstArrangedLineIndex].StartIndex + 1;
_assumedLineExtendsInNonOrientationDirection = _arrangedLines[_firstArrangedLineIndex].TotalExtendsInNonOrientationDirection;
}
// scrolling may have set an invalid index for the first visible line
if (_actualFirstVisibleLineIndex < 0)
{
_actualFirstVisibleLineIndex = 0;
}
if (itemsPerLine > 0)
{
int linesPerPage = (int)Math.Floor(actualExtendsInNonOrientationDirection / _assumedLineExtendsInNonOrientationDirection);
int maxLineIndex = (int)Math.Ceiling((float)numItems / itemsPerLine);
if (_actualFirstVisibleLineIndex > maxLineIndex - linesPerPage)
{
_actualFirstVisibleLineIndex = Math.Max(maxLineIndex - linesPerPage, 0);
}
}
// clear values from previous arrange
_arrangedItems = new FrameworkElement[numItems];
_arrangedLines.Clear();
_firstArrangedLineIndex = 0;
_lastArrangedLineIndex = 0;
// 1) Calculate scroll indices
if (_doScroll)
{ // Calculate last visible child
float spaceLeft = actualExtendsInNonOrientationDirection;
if (invertLayouting)
{
if (_actualLastVisibleLineIndex == int.MaxValue) // when scroll to last item (END) was requested
{
_actualLastVisibleLineIndex = (int)Math.Ceiling((float)numItems / itemsPerLine) - 1;
}
_actualFirstVisibleLineIndex = _actualLastVisibleLineIndex + 1;
int currentLineIndex = _actualLastVisibleLineIndex;
_lastArrangedLineIndex = currentLineIndex;
while (_arrangedLines.Count <= currentLineIndex)
{
_arrangedLines.Add(new LineMeasurement()); // add "unarranged lines" up to the last visible
}
int itemIndex = currentLineIndex * itemsPerLine;
int additionalLinesBefore = 0;
while (currentLineIndex >= 0 && additionalLinesBefore < NUM_ADD_MORE_FOCUS_LINES)
{
LineMeasurement line = CalculateLine(itemIndex, _innerRect.Size, false);
_arrangedLines[currentLineIndex] = line;
_firstArrangedLineIndex = currentLineIndex;
currentLineIndex--;
itemIndex = line.StartIndex - itemsPerLine;
spaceLeft -= line.TotalExtendsInNonOrientationDirection;
if (spaceLeft + DELTA_DOUBLE < 0)
{
additionalLinesBefore++;
}
else
{
_actualFirstVisibleLineIndex--;
}
}
// now add NUM_ADD_MORE_FOCUS_LINES after last visible
itemIndex = _arrangedLines[_lastArrangedLineIndex].EndIndex + 1;
int additionalLinesAfterwards = 0;
while (itemIndex < numItems && additionalLinesAfterwards < NUM_ADD_MORE_FOCUS_LINES)
{
LineMeasurement line = CalculateLine(itemIndex, _innerRect.Size, false);
_arrangedLines.Add(line);
_lastArrangedLineIndex = _arrangedLines.Count - 1;
itemIndex = line.EndIndex + 1;
additionalLinesAfterwards++;
}
}
else
{
_actualLastVisibleLineIndex = _actualFirstVisibleLineIndex - 1;
_firstArrangedLineIndex = Math.Max(_actualFirstVisibleLineIndex - NUM_ADD_MORE_FOCUS_LINES, 0);
int currentLineIndex = _firstArrangedLineIndex;
// add "unarranges lines" up until where we start
while (_arrangedLines.Count < currentLineIndex)
{
_arrangedLines.Add(new LineMeasurement());
}
int itemIndex = currentLineIndex * itemsPerLine;
int additionalLinesAfterwards = 0;
while (itemIndex < numItems && additionalLinesAfterwards < NUM_ADD_MORE_FOCUS_LINES)
{
LineMeasurement line = CalculateLine(itemIndex, _innerRect.Size, false);
_arrangedLines.Add(line);
_lastArrangedLineIndex = currentLineIndex;
currentLineIndex++;
itemIndex = line.EndIndex + 1;
if (currentLineIndex > _actualFirstVisibleLineIndex)
{
spaceLeft -= line.TotalExtendsInNonOrientationDirection;
if (spaceLeft + DELTA_DOUBLE < 0)
{
additionalLinesAfterwards++;
}
else
{
_actualLastVisibleLineIndex++;
}
}
}
}
}
else
{
_actualFirstVisibleLineIndex = 0;
_actualLastVisibleLineIndex = _arrangedLines.Count - 1;
}
// now we know items per line for sure so just calculate it
itemsPerLine = _arrangedLines[_firstArrangedLineIndex].EndIndex - _arrangedLines[_firstArrangedLineIndex].StartIndex + 1;
_assumedLineExtendsInNonOrientationDirection = _arrangedLines[_firstArrangedLineIndex].TotalExtendsInNonOrientationDirection;
// 2) Calculate start position (so the first visible line starts at 0)
startPosition -= (_actualFirstVisibleLineIndex - _firstArrangedLineIndex) * _assumedLineExtendsInNonOrientationDirection;
// 3) Arrange children
if (Orientation == Orientation.Vertical)
{
_totalHeight = actualExtendsInOrientationDirection;
}
else
{
_totalWidth = actualExtendsInOrientationDirection;
}
PointF position = Orientation == Orientation.Vertical ?
new PointF(actualPosition.X + startPosition, actualPosition.Y) :
new PointF(actualPosition.X, actualPosition.Y + startPosition);
foreach (LineMeasurement line in _arrangedLines.Skip(_firstArrangedLineIndex).Take(_lastArrangedLineIndex - _firstArrangedLineIndex + 1))
{
LayoutLine(position, line);
startPosition += line.TotalExtendsInNonOrientationDirection;
if (Orientation == Orientation.Vertical)
{
position = new PointF(actualPosition.X + startPosition, actualPosition.Y);
}
else
{
position = new PointF(actualPosition.X, actualPosition.Y + startPosition);
}
}
// estimate the desired size
var estimatedExtendsInNonOrientationDirection = (float)Math.Ceiling((float)numItems / itemsPerLine) * _assumedLineExtendsInNonOrientationDirection;
if (Orientation == Orientation.Horizontal)
{
_totalHeight = estimatedExtendsInNonOrientationDirection;
}
else
{
_totalWidth = estimatedExtendsInNonOrientationDirection;
}
// keep one more item, because we did use it in CalcLine (and need always one more to find the last item not fitting on the line)
// -> if we dont, it will always be newlyCreated and we keep calling Arrange since the new item recursively sets the parent invalid
_itemProvider.Keep(_arrangedLines[_firstArrangedLineIndex].StartIndex, _arrangedLines[_lastArrangedLineIndex].EndIndex + 1);
}
else
{
_actualFirstVisibleLineIndex = 0;
_actualLastVisibleLineIndex = -1;
}
}
if (fireScrolled)
{
InvokeScrolled();
}
}