internal void RemoveRange(int startIndex, int endIndex)
{
for (int i = startIndex; i <= endIndex; i++)
{
if (i > _items.Count)
{
break;
}
StaggeredItem item = _items[i];
item.Height = 0;
item.Top = 0;
// We must recycle all elements to ensure that it gets the correct context
RecycleElementAt(i);
}
foreach (var kvp in _columnLayout)
{
StaggeredColumnLayout layout = kvp.Value;
for (int i = 0; i < layout.Count; i++)
{
if ((startIndex <= layout[i].Index) && (layout[i].Index <= endIndex))
{
int numToRemove = layout.Count - i;
layout.RemoveRange(i, numToRemove);
break;
}
}
}
}
internal void AddItemToColumn(StaggeredItem item, int columnIndex)
{
if (_columnLayout.TryGetValue(columnIndex, out StaggeredColumnLayout columnLayout) == false)
{
columnLayout = new StaggeredColumnLayout();
_columnLayout[columnIndex] = columnLayout;
}
if (columnLayout.Contains(item) == false)
{
columnLayout.Add(item);
}
}
internal StaggeredItem GetItemAt(int index)
{
if (index < 0)
{
throw new IndexOutOfRangeException();
}
if (index <= (_items.Count - 1))
{
return(_items[index]);
}
else
{
StaggeredItem item = new StaggeredItem(index);
_items.Add(item);
return(item);
}
}
/// <inheritdoc/>
protected override Size ArrangeOverride(VirtualizingLayoutContext context, Size finalSize)
{
if ((context.RealizationRect.Width == 0) && (context.RealizationRect.Height == 0))
{
return(finalSize);
}
var state = (StaggeredLayoutState)context.LayoutState;
// Cycle through each column and arrange the items that are within the realization bounds
for (int columnIndex = 0; columnIndex < state.NumberOfColumns; columnIndex++)
{
StaggeredColumnLayout layout = state.GetColumnLayout(columnIndex);
for (int i = 0; i < layout.Count; i++)
{
StaggeredItem item = layout[i];
double bottom = item.Top + item.Height;
if (bottom < context.RealizationRect.Top)
{
// element is above the realization bounds
continue;
}
if (item.Top <= context.RealizationRect.Bottom)
{
double itemHorizontalOffset = (state.ColumnWidth * columnIndex) + (ColumnSpacing * columnIndex);
Rect bounds = new Rect(itemHorizontalOffset, item.Top, state.ColumnWidth, item.Height);
UIElement element = context.GetOrCreateElementAt(item.Index);
element.Arrange(bounds);
}
else
{
break;
}
}
}
return(finalSize);
}
/// <inheritdoc/>
protected override Size MeasureOverride(VirtualizingLayoutContext context, Size availableSize)
{
if (context.ItemCount == 0)
{
return(new Size(availableSize.Width, 0));
}
if ((context.RealizationRect.Width == 0) && (context.RealizationRect.Height == 0))
{
return(new Size(availableSize.Width, 0.0));
}
var state = (StaggeredLayoutState)context.LayoutState;
double availableWidth = availableSize.Width;
double availableHeight = availableSize.Height;
double columnWidth = Math.Min(DesiredColumnWidth, availableWidth);
if (columnWidth != state.ColumnWidth)
{
// The items will need to be remeasured
state.Clear();
}
state.ColumnWidth = Math.Min(DesiredColumnWidth, availableWidth);
int numColumns = Math.Max(1, (int)Math.Floor(availableWidth / state.ColumnWidth));
// adjust for column spacing on all columns expect the first
double totalWidth = state.ColumnWidth + ((numColumns - 1) * (state.ColumnWidth + ColumnSpacing));
if (totalWidth > availableWidth)
{
numColumns--;
}
else if (double.IsInfinity(availableWidth))
{
availableWidth = totalWidth;
}
if (numColumns != state.NumberOfColumns)
{
// The items will not need to be remeasured, but they will need to go into new columns
state.ClearColumns();
}
if (RowSpacing != state.RowSpacing)
{
// If the RowSpacing changes the height of the rows will be different.
// The columns stores the height so we'll want to clear them out to
// get the proper height
state.ClearColumns();
state.RowSpacing = RowSpacing;
}
var columnHeights = new double[numColumns];
var itemsPerColumn = new int[numColumns];
var deadColumns = new HashSet <int>();
for (int i = 0; i < context.ItemCount; i++)
{
var columnIndex = GetColumnIndex(columnHeights);
bool measured = false;
StaggeredItem item = state.GetItemAt(i);
if (item.Height == 0)
{
// Item has not been measured yet. Get the element and store the values
item.Element = context.GetOrCreateElementAt(i);
item.Element.Measure(new Size(state.ColumnWidth, availableHeight));
item.Height = item.Element.DesiredSize.Height;
measured = true;
}
double spacing = itemsPerColumn[columnIndex] > 0 ? RowSpacing : 0;
item.Top = columnHeights[columnIndex] + spacing;
double bottom = item.Top + item.Height;
columnHeights[columnIndex] = bottom;
itemsPerColumn[columnIndex]++;
state.AddItemToColumn(item, columnIndex);
if (bottom < context.RealizationRect.Top)
{
// The bottom of the element is above the realization area
if (item.Element != null)
{
context.RecycleElement(item.Element);
item.Element = null;
}
}
else if (item.Top > context.RealizationRect.Bottom)
{
// The top of the element is below the realization area
if (item.Element != null)
{
context.RecycleElement(item.Element);
item.Element = null;
}
deadColumns.Add(columnIndex);
}
else if (measured == false)
{
// We ALWAYS want to measure an item that will be in the bounds
item.Element = context.GetOrCreateElementAt(i);
item.Element.Measure(new Size(state.ColumnWidth, availableHeight));
if (item.Height != item.Element.DesiredSize.Height)
{
// this item changed size; we need to recalculate layout for everything after this
state.RemoveFromIndex(i + 1);
item.Height = item.Element.DesiredSize.Height;
columnHeights[columnIndex] = item.Top + item.Height;
}
}
if (deadColumns.Count == numColumns)
{
break;
}
}
double desiredHeight = state.GetHeight();
return(new Size(availableWidth, desiredHeight));
}