9539if (_scrollData == null) { _scrollData = new ScrollData(); }

449_scrollData._computedOffset.X = startingOffset; 453_scrollData._computedOffset.Y = startingOffset; 483if (!DoubleUtil.AreClose(scrollX, _scrollData._offset.X)) 485Vector oldViewportOffset = _scrollData._offset; 488_scrollData._offset.X = scrollX; 491OnViewportOffsetChanged(oldViewportOffset, _scrollData._offset); 496_scrollData.SetHorizontalScrollType(oldViewportOffset.X, scrollX); 523_scrollData._offset.X = Math.Floor(_scrollData._offset.X); 524_scrollData._computedOffset.X = Math.Floor(_scrollData._computedOffset.X); 532_scrollData._offset.X = UIElement.RoundLayoutValue(_scrollData._offset.X, dpi.DpiScaleX); 533_scrollData._computedOffset.X = UIElement.RoundLayoutValue(_scrollData._computedOffset.X, dpi.DpiScaleX); 555_scrollData._computedOffset.X = startingOffset; 569_scrollData._offset.X = ScrollContentPresenter.CoerceOffset(scrollX, _scrollData._extent.Width, _scrollData._viewport.Width); 570_scrollData._computedOffset.X = _scrollData._offset.X; 578_scrollData._offset, _scrollData._extent, _scrollData._computedOffset); 611if (!DoubleUtil.AreClose(scrollY, _scrollData._offset.Y)) 613Vector oldViewportOffset = _scrollData._offset; 616_scrollData._offset.Y = scrollY; 619OnViewportOffsetChanged(oldViewportOffset, _scrollData._offset); 625_scrollData.SetVerticalScrollType(oldViewportOffset.Y, scrollY); 651_scrollData._offset.Y = Math.Floor(_scrollData._offset.Y); 652_scrollData._computedOffset.Y = Math.Floor(_scrollData._computedOffset.Y); 660_scrollData._offset.Y = UIElement.RoundLayoutValue(_scrollData._offset.Y, dpi.DpiScaleY); 661_scrollData._computedOffset.Y = UIElement.RoundLayoutValue(_scrollData._computedOffset.Y, dpi.DpiScaleY); 683_scrollData._computedOffset.Y = startingOffset; 697_scrollData._offset.Y = ScrollContentPresenter.CoerceOffset(scrollY, _scrollData._extent.Height, _scrollData._viewport.Height); 698_scrollData._computedOffset.Y = _scrollData._offset.Y; 712_scrollData._offset, _scrollData._extent, _scrollData._computedOffset); 750double expectedDistanceBetweenViewports = (isHorizontal ? _scrollData._offset.X - _scrollData._computedOffset.X : _scrollData._offset.Y - _scrollData._computedOffset.Y); 758if (_scrollData._firstContainerInViewport != null) 770_scrollData._offset.X += expectedDistanceBetweenViewports; 774_scrollData._offset.Y += expectedDistanceBetweenViewports; 778if (_scrollData._firstContainerInViewport == null) 780_scrollData._firstContainerInViewport = ComputeFirstContainerInViewport( 791out _scrollData._firstContainerOffsetFromViewport); 793if (_scrollData._firstContainerInViewport != null) 795_scrollData._expectedDistanceBetweenViewports = expectedDistanceBetweenViewports; 804_scrollData._expectedDistanceBetweenViewports += expectedDistanceBetweenViewports; 810_scrollData._expectedDistanceBetweenViewports, 811_scrollData._firstContainerInViewport, 812_scrollData._firstContainerOffsetFromViewport); 829Debug.Assert(_scrollData._firstContainerInViewport != null, "Must have an anchor element"); 833if (itemsControl == null || !VisualTreeHelper.IsAncestorOf(this, _scrollData._firstContainerInViewport)) 844_scrollData._expectedDistanceBetweenViewports, 845_scrollData._firstContainerInViewport); 874FrameworkElement prevFirstContainerInViewport = _scrollData._firstContainerInViewport; 875double prevFirstContainerOffsetFromViewport = _scrollData._firstContainerOffsetFromViewport; 876double prevFirstContainerOffset = FindScrollOffset(_scrollData._firstContainerInViewport); 892bool success = (LayoutDoubleUtil.AreClose(_scrollData._expectedDistanceBetweenViewports, actualDistanceBetweenViewports)); 909double diff = actualDistanceBetweenViewports - _scrollData._expectedDistanceBetweenViewports; 931computedOffset = _scrollData._computedOffset.X; 932maxOffset = _scrollData._extent.Width - _scrollData._viewport.Width; 936computedOffset = _scrollData._computedOffset.Y; 937maxOffset = _scrollData._extent.Height - _scrollData._viewport.Height; 949_scrollData._computedOffset.X = currFirstContainerOffset - currFirstContainerOffsetFromViewport; 950_scrollData._offset.X = _scrollData._computedOffset.X; 954_scrollData._computedOffset.Y = currFirstContainerOffset - currFirstContainerOffsetFromViewport; 955_scrollData._offset.Y = _scrollData._computedOffset.Y; 967_scrollData._offset); 977_scrollData._computedOffset.X = prevFirstContainerOffset - prevFirstContainerOffsetFromViewport; 979actualOffset = _scrollData._computedOffset.X + actualDistanceBetweenViewports; 980expectedOffset = _scrollData._computedOffset.X + _scrollData._expectedDistanceBetweenViewports; 981maxOffset = _scrollData._extent.Width - _scrollData._viewport.Width; 990_scrollData._computedOffset.X = actualOffset; 991_scrollData._offset.X = actualOffset; 996_scrollData._offset.X = expectedOffset; 1002_scrollData._offset.X = expectedOffset; 1007_scrollData._computedOffset.Y = prevFirstContainerOffset - prevFirstContainerOffsetFromViewport; 1009actualOffset = _scrollData._computedOffset.Y + actualDistanceBetweenViewports; 1010expectedOffset = _scrollData._computedOffset.Y + _scrollData._expectedDistanceBetweenViewports; 1011maxOffset = _scrollData._extent.Height - _scrollData._viewport.Height; 1020_scrollData._computedOffset.Y = actualOffset; 1021_scrollData._offset.Y = actualOffset; 1026_scrollData._offset.Y = expectedOffset; 1032_scrollData._offset.Y = expectedOffset; 1039remeasure, expectedOffset, actualOffset, _scrollData._offset, _scrollData._computedOffset); 1085if (_scrollData == null) 1088if (_scrollData._firstContainerInViewport != null) 1090DependencyObject element = _scrollData._firstContainerInViewport; 1104_scrollData._firstContainerInViewport = null; 1105_scrollData._firstContainerOffsetFromViewport = 0; 1106_scrollData._expectedDistanceBetweenViewports = 0; 1513alignTop = (_scrollData._bringIntoViewLeafContainer == visual && AlignTopOfBringIntoViewContainer); 1514alignBottom = (_scrollData._bringIntoViewLeafContainer == visual && 1531newOffset.X = ScrollContentPresenter.CoerceOffset(newOffset.X, _scrollData._extent.Width, _scrollData._viewport.Width); 1532newOffset.Y = ScrollContentPresenter.CoerceOffset(newOffset.Y, _scrollData._extent.Height, _scrollData._viewport.Height); 1534if (!LayoutDoubleUtil.AreClose(newOffset.X, _scrollData._offset.X) || 1535!LayoutDoubleUtil.AreClose(newOffset.Y, _scrollData._offset.Y)) 1538if (visual != _scrollData._bringIntoViewLeafContainer) 1540_scrollData._bringIntoViewLeafContainer = visual; 1545Vector oldOffset = _scrollData._offset; 1546_scrollData._offset = newOffset; 1551_scrollData._offset, 1553_scrollData._bringIntoViewLeafContainer); 1561_scrollData.SetHorizontalScrollType(oldOffset.X, newOffset.X); 1562_scrollData.SetVerticalScrollType(oldOffset.Y, newOffset.Y); 1571_scrollData._computedOffset = newOffset; 1586_scrollData._bringIntoViewLeafContainer = null; 1810if (_scrollData == null) { return false; } 1811return _scrollData._allowHorizontal; 1816if (_scrollData._allowHorizontal != value) 1818_scrollData._allowHorizontal = value; 1833if (_scrollData == null) { return false; } 1834return _scrollData._allowVertical; 1839if (_scrollData._allowVertical != value) 1841_scrollData._allowVertical = value; 1854if (_scrollData == null) { return 0.0; } 1855return _scrollData._extent.Width; 1866if (_scrollData == null) { return 0.0; } 1867return _scrollData._extent.Height; 1878if (_scrollData == null) { return 0.0; } 1879return _scrollData._viewport.Width; 1890if (_scrollData == null) { return 0.0; } 1891return _scrollData._viewport.Height; 1903if (_scrollData == null) { return 0.0; } 1904return _scrollData._computedOffset.X; 1916if (_scrollData == null) { return 0.0; } 1917return _scrollData._computedOffset.Y; 1930if (_scrollData == null) return null; 1931return _scrollData._scrollOwner; 1936if (value != _scrollData._scrollOwner) 1939_scrollData._scrollOwner = value; 2597if (IsScrolling && _scrollData._firstContainerInViewport != null && !areContainersUniformlySized) 2638_scrollData._offset.X += delta; 2642_scrollData._offset.Y += delta; 2653"newVpOff:", _scrollData._offset); 3256return StackPanel.StackMeasureHelper(this, _scrollData, constraint); 3261return StackPanel.StackArrangeHelper(this, _scrollData, arrangeSize); 3546"ext:", IsScrolling ? _scrollData._extent : Size.Empty, 3610_scrollData._maxDesiredSize = new Size(); 3878_scrollData._extent.Width = distance; 3882_scrollData._extent.Height = distance; 3887ScrollTracer.Trace(this, ScrollTraceOp.UpdateExtent, "ext:", _scrollData._extent); 4310offsetX = _scrollData._offset.X; 4311offsetY = _scrollData._offset.Y; 4312extent = _scrollData._extent; 4313viewportSize = _scrollData._viewport; 4314scrollGeneration = _scrollData._scrollGeneration; 4318_scrollData._maxDesiredSize = new Size(); 4343WasLastMeasurePassAnchored = (_scrollData._firstContainerInViewport != null) || (_scrollData._bringIntoViewLeafContainer != null); 4641_scrollData._bringIntoViewLeafContainer = null; 4649_scrollData._offset = _scrollData._computedOffset; 4775if (DoubleUtil.GreaterThan(extendedViewport.X + extendedViewport.Width, _scrollData._extent.Width)) 4782extendedViewport.Width = Math.Max(_scrollData._extent.Width - extendedViewport.X, 0.0); 4815if (DoubleUtil.GreaterThan(extendedViewport.X + extendedViewport.Width / approxSizeOfLogicalUnit, _scrollData._extent.Width)) 4822extendedViewport.Width = Math.Max(_scrollData._extent.Width - extendedViewport.X, 0.0) * approxSizeOfLogicalUnit; 4891if (DoubleUtil.GreaterThan(extendedViewport.Y + extendedViewport.Height, _scrollData._extent.Height)) 4898extendedViewport.Height = Math.Max(_scrollData._extent.Height - extendedViewport.Y, 0.0); 4931if (DoubleUtil.GreaterThan(extendedViewport.Y + extendedViewport.Height / approxSizeOfLogicalUnit, _scrollData._extent.Height)) 4938extendedViewport.Height = Math.Max(_scrollData._extent.Height - extendedViewport.Y, 0.0) * approxSizeOfLogicalUnit; 4963if (!_scrollData.IsEmpty) 4972if (!_scrollData.IsEmpty) 5722++_scrollData._scrollGeneration; 8407rcChild.Y = -1.0 * _scrollData._computedOffset.Y; 8413rcChild.X = -1.0 * _scrollData._computedOffset.X; 8418rcChild.X = -1.0 * _scrollData._computedOffset.X; 8419rcChild.Y = -1.0 * _scrollData._computedOffset.Y; 9539if (_scrollData == null) { _scrollData = new ScrollData(); } 9549element._scrollData.ClearLayout(); 9591Vector offsetForScrollViewerRemeasure = _scrollData._offset; 9635stackPixelSize.Height = _scrollData._extent.Height; 9642_scrollData._maxDesiredSize.Height = Math.Max(_scrollData._maxDesiredSize.Height, stackPixelSize.Height); 9643stackPixelSize.Height = _scrollData._maxDesiredSize.Height; 9662stackPixelSize.Width = _scrollData._extent.Width; 9669_scrollData._maxDesiredSize.Width = Math.Max(_scrollData._maxDesiredSize.Width, stackPixelSize.Width); 9670stackPixelSize.Width = _scrollData._maxDesiredSize.Width; 9726"o:", _scrollData._offset, 9742isHorizontal ? (!DoubleUtil.AreClose(computedViewportOffset.X, _scrollData._offset.X) || 9743(IsScrollActive && computedViewportOffset.X > 0.0 && DoubleUtil.GreaterThanOrClose(computedViewportOffset.X, _scrollData.Extent.Width-_scrollData.Viewport.Width))) 9744: (!DoubleUtil.AreClose(computedViewportOffset.Y, _scrollData._offset.Y) || 9745(IsScrollActive && computedViewportOffset.Y > 0.0 && DoubleUtil.GreaterThanOrClose(computedViewportOffset.Y, _scrollData.Extent.Height-_scrollData.Viewport.Height))); 9747isHorizontal ? (!DoubleUtil.AreClose(computedViewportOffset.Y, _scrollData._offset.Y) || 9748(IsScrollActive && computedViewportOffset.Y > 0.0 && DoubleUtil.GreaterThanOrClose(computedViewportOffset.Y, _scrollData.Extent.Height-_scrollData.Viewport.Height))) 9749: (!DoubleUtil.AreClose(computedViewportOffset.X, _scrollData._offset.X) || 9750(IsScrollActive && computedViewportOffset.X > 0.0 && DoubleUtil.GreaterThanOrClose(computedViewportOffset.X, _scrollData.Extent.Width-_scrollData.Viewport.Width))); 9786_scrollData.HorizontalScrollType = ScrollType.ToEnd; 9809_scrollData.VerticalScrollType = ScrollType.ToEnd; 9843bool viewportSizeChanged = !DoubleUtil.AreClose(viewportSize, _scrollData._viewport); 9844bool extentSizeChanged = !DoubleUtil.AreClose(extentSize, _scrollData._extent); 9845bool computedViewportOffsetChanged = !DoubleUtil.AreClose(computedViewportOffset, _scrollData._computedOffset); 9850extentWidthChanged = !DoubleUtil.AreClose(extentSize.Width, _scrollData._extent.Width); 9851extentHeightChanged = !DoubleUtil.AreClose(extentSize.Height, _scrollData._extent.Height); 9990!DoubleUtil.AreClose(_scrollData._viewport.Width, viewportSize.Width)) 9996"vpSz:", _scrollData._viewport.Width, viewportSize.Width, 9997"newOff:", _scrollData._offset); 10006viewportSize.Width = _scrollData._viewport.Width; 10020if (_scrollData.HorizontalScrollType == ScrollType.ToEnd || 10028"ext:", _scrollData._extent.Width, extentSize.Width, 10034_scrollData.HorizontalScrollType = ScrollType.ToEnd; 10043else if (_scrollData.HorizontalScrollType == ScrollType.Absolute) 10045if (!DoubleUtil.AreClose(_scrollData._extent.Width, 0) && 10050if (!LayoutDoubleUtil.AreClose(computedViewportOffset.X/extentSize.Width, _scrollData._offset.X/_scrollData._extent.Width)) 10053viewportOffset.X = (extentSize.Width * _scrollData._offset.X) / _scrollData._extent.Width; 10059if (!LayoutDoubleUtil.AreClose(Math.Floor(computedViewportOffset.X)/extentSize.Width, Math.Floor(_scrollData._offset.X)/_scrollData._extent.Width)) 10062viewportOffset.X = Math.Floor((extentSize.Width * Math.Floor(_scrollData._offset.X)) / _scrollData._extent.Width); 10070"expRat:", _scrollData._offset.X, _scrollData._extent.Width, (_scrollData._offset.X/_scrollData._extent.Width), 10087if (_scrollData.VerticalScrollType == ScrollType.ToEnd || 10096"ext:", _scrollData._extent.Height, extentSize.Height, 10102_scrollData.VerticalScrollType = ScrollType.ToEnd; 10110else if (_scrollData.VerticalScrollType == ScrollType.Absolute) 10112if (!DoubleUtil.AreClose(_scrollData._extent.Height, 0) && 10115if (!LayoutDoubleUtil.AreClose(computedViewportOffset.Y/extentSize.Height, _scrollData._offset.Y/_scrollData._extent.Height)) 10118viewportOffset.Y = (extentSize.Height * _scrollData._offset.Y) / _scrollData._extent.Height; 10125"expRat:", _scrollData._offset.Y, _scrollData._extent.Height, (_scrollData._offset.Y/_scrollData._extent.Height), 10207!DoubleUtil.AreClose(_scrollData._viewport.Height, viewportSize.Height)) 10213"vpSz:", _scrollData._viewport.Height, viewportSize.Height, 10214"newOff:", _scrollData._offset); 10223viewportSize.Height = _scrollData._viewport.Height; 10237if (_scrollData.VerticalScrollType == ScrollType.ToEnd || 10245"ext:", _scrollData._extent.Height, extentSize.Height, 10251_scrollData.VerticalScrollType = ScrollType.ToEnd; 10260else if (_scrollData.VerticalScrollType == ScrollType.Absolute) 10262if (!DoubleUtil.AreClose(_scrollData._extent.Height, 0) && 10267if (!LayoutDoubleUtil.AreClose(computedViewportOffset.Y/extentSize.Height, _scrollData._offset.Y/_scrollData._extent.Height)) 10270viewportOffset.Y = (extentSize.Height * _scrollData._offset.Y) / _scrollData._extent.Height; 10276if (!LayoutDoubleUtil.AreClose(Math.Floor(computedViewportOffset.Y)/extentSize.Height, Math.Floor(_scrollData._offset.Y)/_scrollData._extent.Height)) 10279viewportOffset.Y = Math.Floor((extentSize.Height * Math.Floor(_scrollData._offset.Y)) / _scrollData._extent.Height); 10286"expRat:", _scrollData._offset.Y, _scrollData._extent.Height, (_scrollData._offset.Y/_scrollData._extent.Height), 10303if (_scrollData.HorizontalScrollType == ScrollType.ToEnd || 10312"ext:", _scrollData._extent.Width, extentSize.Width, 10318_scrollData.HorizontalScrollType = ScrollType.ToEnd; 10326else if (_scrollData.HorizontalScrollType == ScrollType.Absolute) 10328if (!DoubleUtil.AreClose(_scrollData._extent.Width, 0) && 10331if (!LayoutDoubleUtil.AreClose(computedViewportOffset.X/extentSize.Width, _scrollData._offset.X/_scrollData._extent.Width)) 10334viewportOffset.X = (extentSize.Width * _scrollData._offset.X) / _scrollData._extent.Width; 10341"expRat:", _scrollData._offset.X, _scrollData._extent.Width, (_scrollData._offset.X/_scrollData._extent.Width), 10357if (isHorizontal && _scrollData.HorizontalScrollType == ScrollType.ToEnd) 10361if (!isHorizontal && _scrollData.VerticalScrollType == ScrollType.ToEnd) 10375viewportSizeChanged = !DoubleUtil.AreClose(viewportSize, _scrollData._viewport); 10380"off:", _scrollData._offset, viewportOffset, 10381"ext:", _scrollData._extent, extentSize, 10382"co:", _scrollData._computedOffset, computedViewportOffset, 10383"vp:", _scrollData._viewport, viewportSize); 10389Vector oldViewportOffset = _scrollData._computedOffset; 10390Size oldViewportSize = _scrollData._viewport; 10392_scrollData._viewport = viewportSize; 10393_scrollData._extent = extentSize; 10394_scrollData._computedOffset = computedViewportOffset; 10411_scrollData._offset = viewportOffset; 10484stackPixelSize.Height = _scrollData._extent.Height; 10491_scrollData._maxDesiredSize.Height = Math.Max(_scrollData._maxDesiredSize.Height, stackPixelSize.Height); 10492stackPixelSize.Height = _scrollData._maxDesiredSize.Height; 10511stackPixelSize.Width = _scrollData._extent.Width; 10518_scrollData._maxDesiredSize.Width = Math.Max(_scrollData._maxDesiredSize.Width, stackPixelSize.Width); 10519stackPixelSize.Width = _scrollData._maxDesiredSize.Width; 10571bool viewportSizeChanged = !DoubleUtil.AreClose(viewportSize, _scrollData._viewport); 10572bool extentSizeChanged = !DoubleUtil.AreClose(extentSize, _scrollData._extent); 10573bool computedViewportOffsetChanged = !DoubleUtil.AreClose(computedViewportOffset, _scrollData._computedOffset); 10601viewportOffset = _scrollData._offset; 10617viewportOffset = _scrollData._offset; 10630bool wasViewportOffsetCoerced = !DoubleUtil.AreClose(computedViewportOffset.X, _scrollData._offset.X); 10663!DoubleUtil.AreClose(_scrollData._viewport.Width, viewportSize.Width)) 10666viewportOffset.X = _scrollData._offset.X; 10671viewportSize.Width = _scrollData._viewport.Width; 10676if (!remeasure && extentSizeChanged && !DoubleUtil.AreClose(_scrollData._extent.Width, extentSize.Width)) 10699viewportOffset.X = _scrollData._offset.X; 10713(_scrollData._firstContainerInViewport == null && computedViewportOffsetChanged && !LayoutDoubleUtil.AreClose(computedViewportOffset.X, _scrollData._computedOffset.X)); 10716!DoubleUtil.AreClose(_scrollData._extent.Width, 0) && 10721if (!LayoutDoubleUtil.AreClose(computedViewportOffset.X/extentSize.Width, _scrollData._offset.X/_scrollData._extent.Width)) 10724viewportOffset.X = (extentSize.Width * _scrollData._offset.X) / _scrollData._extent.Width; 10730if (!LayoutDoubleUtil.AreClose(Math.Floor(computedViewportOffset.X)/extentSize.Width, Math.Floor(_scrollData._offset.X)/_scrollData._extent.Width)) 10733viewportOffset.X = Math.Floor((extentSize.Width * Math.Floor(_scrollData._offset.X)) / _scrollData._extent.Width); 10761bool wasViewportOffsetCoerced = !DoubleUtil.AreClose(computedViewportOffset.Y, _scrollData._offset.Y); 10794!DoubleUtil.AreClose(_scrollData._viewport.Height, viewportSize.Height)) 10797viewportOffset.Y = _scrollData._offset.Y; 10802viewportSize.Height = _scrollData._viewport.Height; 10807if (!remeasure && extentSizeChanged && !DoubleUtil.AreClose(_scrollData._extent.Height, extentSize.Height)) 10830viewportOffset.Y = _scrollData._offset.Y; 10844(_scrollData._firstContainerInViewport == null && computedViewportOffsetChanged && !LayoutDoubleUtil.AreClose(computedViewportOffset.Y, _scrollData._computedOffset.Y)); 10847!DoubleUtil.AreClose(_scrollData._extent.Height, 0) && 10852if (!LayoutDoubleUtil.AreClose(computedViewportOffset.Y/extentSize.Height, _scrollData._offset.Y/_scrollData._extent.Height)) 10855viewportOffset.Y = (extentSize.Height * _scrollData._offset.Y) / _scrollData._extent.Height; 10861if (!LayoutDoubleUtil.AreClose(Math.Floor(computedViewportOffset.Y)/extentSize.Height, Math.Floor(_scrollData._offset.Y)/_scrollData._extent.Height)) 10864viewportOffset.Y = Math.Floor((extentSize.Height * Math.Floor(_scrollData._offset.Y)) / _scrollData._extent.Height); 10887viewportSizeChanged = !DoubleUtil.AreClose(viewportSize, _scrollData._viewport); 10892Vector oldViewportOffset = _scrollData._computedOffset; 10893Size oldViewportSize = _scrollData._viewport; 10895_scrollData._viewport = viewportSize; 10896_scrollData._extent = extentSize; 10897_scrollData._computedOffset = computedViewportOffset; 10914_scrollData._offset = viewportOffset; 11141viewportOffset = _scrollData._computedOffset.X; 11148viewportOffset = _scrollData._computedOffset.Y; 11189firstChildInView = (int)_scrollData._computedOffset.X; 11190viewportSize = (int)_scrollData._viewport.Width; 11194firstChildInView = (int)_scrollData._computedOffset.Y; 11195viewportSize = (int)_scrollData._viewport.Height; 11320get { return (_scrollData != null) && (_scrollData._scrollOwner != null); } 11487_scrollData.HorizontalScrollType = ScrollType.None; 11488_scrollData.VerticalScrollType = ScrollType.None; 11592get { return _scrollData?._bringIntoViewLeafContainer ?? null; } 11597get { return _scrollData?._firstContainerInViewport ?? null; } 11602get { return _scrollData?._firstContainerOffsetFromViewport ?? 0.0; } 11607get { return _scrollData?._expectedDistanceBetweenViewports ?? 0.0; } 12961_offset = _scrollData._offset, 12962_extent = _scrollData._extent, 12963_computedOffset = _scrollData._computedOffset, 12964_viewport = _scrollData._viewport