public void SetContext(VirtualizingLayoutContext virtualContext) => _context = virtualContext;
/// <summary>
/// Provides the behavior for the "Measure" pass of the layout cycle. Classes can override
/// this method to define their own "Measure" pass behavior.
/// </summary>
/// <param name="context">
/// The context object that facilitates communication between the layout and its host
/// container.
/// </param>
/// <param name="availableSize">
/// The available size that this object can give to child objects. Infinity can be
/// specified as a value to indicate that the object will size to whatever content is
/// available.
/// </param>
/// <returns>
/// The size that this object determines it needs during layout, based on its calculations
/// of the allocated sizes for child objects or based on other considerations such as a
/// fixed container size.
/// </returns>
protected internal abstract Size MeasureOverride(
VirtualizingLayoutContext context,
Size availableSize);
/// <summary>
/// When implemented in a derived class, provides the behavior for the "Arrange" pass of
/// layout. Classes can override this method to define their own "Arrange" pass behavior.
/// </summary>
/// <param name="context">
/// The context object that facilitates communication between the layout and its host
/// container.
/// </param>
/// <param name="finalSize">
/// The final area within the container that this object should use to arrange itself and
/// its children.
/// </param>
/// <returns>The actual size that is used after the element is arranged in layout.</returns>
protected internal virtual Size ArrangeOverride(
VirtualizingLayoutContext context,
Size finalSize) => finalSize;
/// <summary>
/// Notifies the layout when the data collection assigned to the container element (Items)
/// has changed.
/// </summary>
/// <param name="context">
/// The context object that facilitates communication between the layout and its host
/// container.
/// </param>
/// <param name="source">The data source.</param>
/// <param name="args">Data about the collection change.</param>
/// <remarks>
/// Override <see cref="OnItemsChangedCore(VirtualizingLayoutContext, object, NotifyCollectionChangedEventArgs)"/>
/// to provide the behavior for this method in a derived class.
/// </remarks>
public void OnItemsChanged(
VirtualizingLayoutContext context,
object?source,
NotifyCollectionChangedEventArgs args) => OnItemsChangedCore(context, source, args);
/// <summary>
/// When overridden in a derived class, removes any state the layout previously stored on
/// the ILayoutable container.
/// </summary>
/// <param name="context">
/// The context object that facilitates communication between the layout and its host
/// container.
/// </param>
protected internal virtual void UninitializeForContextCore(VirtualizingLayoutContext context)
{
}
/// <inheritdoc />
protected internal override void UninitializeForContextCore(VirtualizingLayoutContext context)
{
context.LayoutState = null;
base.UninitializeForContextCore(context);
}
/// <summary>
/// Notifies the layout when the data collection assigned to the container element (Items)
/// has changed.
/// </summary>
/// <param name="context">
/// The context object that facilitates communication between the layout and its host
/// container.
/// </param>
/// <param name="source">The data source.</param>
/// <param name="args">Data about the collection change.</param>
protected internal virtual void OnItemsChangedCore(
VirtualizingLayoutContext context,
object?source,
NotifyCollectionChangedEventArgs args) => InvalidateMeasure();
/// <inheritdoc />
protected internal override Size MeasureOverride(VirtualizingLayoutContext context, Size availableSize)
{
var totalMeasure = UvMeasure.Zero;
var parentMeasure = new UvMeasure(Orientation, availableSize.Width, availableSize.Height);
var spacingMeasure = new UvMeasure(Orientation, HorizontalSpacing, VerticalSpacing);
var realizationBounds = new UvBounds(Orientation, context.RealizationRect);
var position = UvMeasure.Zero;
var state = (WrapLayoutState)context.LayoutState !;
if (state.Orientation != Orientation)
{
state.SetOrientation(Orientation);
}
if (spacingMeasure.Equals(state.Spacing) == false)
{
state.ClearPositions();
state.Spacing = spacingMeasure;
}
if (state.AvailableU != parentMeasure.U)
{
state.ClearPositions();
state.AvailableU = parentMeasure.U;
}
double currentV = 0;
for (int i = 0; i < context.ItemCount; i++)
{
bool measured = false;
WrapItem item = state.GetItemAt(i);
if (item.Measure == null)
{
item.Element = context.GetOrCreateElementAt(i);
item.Element.Measure(availableSize);
item.Measure = new UvMeasure(Orientation, item.Element.DesiredSize.Width, item.Element.DesiredSize.Height);
measured = true;
}
UvMeasure currentMeasure = item.Measure.Value;
if (currentMeasure.U == 0)
{
continue; // ignore collapsed items
}
if (item.Position == null)
{
if (parentMeasure.U < position.U + currentMeasure.U)
{
// New Row
position.U = 0;
position.V += currentV + spacingMeasure.V;
currentV = 0;
}
item.Position = position;
}
position = item.Position.Value;
double vEnd = position.V + currentMeasure.V;
if (vEnd < realizationBounds.VMin)
{
// Item is "above" the bounds
if (item.Element != null)
{
context.RecycleElement(item.Element);
item.Element = null;
}
}
else if (position.V > realizationBounds.VMax)
{
// Item is "below" the bounds.
if (item.Element != null)
{
context.RecycleElement(item.Element);
item.Element = null;
}
// We don't need to measure anything below the bounds
break;
}
else if (measured == false)
{
// Always measure elements that are within the bounds
item.Element = context.GetOrCreateElementAt(i);
item.Element.Measure(availableSize);
currentMeasure = new UvMeasure(Orientation, item.Element.DesiredSize.Width, item.Element.DesiredSize.Height);
if (currentMeasure.Equals(item.Measure) == false)
{
// this item changed size; we need to recalculate layout for everything after this
state.RemoveFromIndex(i + 1);
item.Measure = currentMeasure;
// did the change make it go into the new row?
if (parentMeasure.U < position.U + currentMeasure.U)
{
// New Row
position.U = 0;
position.V += currentV + spacingMeasure.V;
currentV = 0;
}
item.Position = position;
}
}
position.U += currentMeasure.U + spacingMeasure.U;
currentV = Math.Max(currentMeasure.V, currentV);
}
// update value with the last line
// if the the last loop is(parentMeasure.U > currentMeasure.U + lineMeasure.U) the total isn't calculated then calculate it
// if the last loop is (parentMeasure.U > currentMeasure.U) the currentMeasure isn't added to the total so add it here
// for the last condition it is zeros so adding it will make no difference
// this way is faster than an if condition in every loop for checking the last item
totalMeasure.U = parentMeasure.U;
// Propagating an infinite size causes a crash. This can happen if the parent is scrollable and infinite in the opposite
// axis to the panel. Clearing to zero prevents the crash.
// This is likely an incorrect use of the control by the developer, however we need stability here so setting a default that wont crash.
if (double.IsInfinity(totalMeasure.U))
{
totalMeasure.U = 0.0;
}
totalMeasure.V = state.GetHeight();
totalMeasure.U = Math.Ceiling(totalMeasure.U);
return(Orientation == Orientation.Horizontal ? new Size(totalMeasure.U, totalMeasure.V) : new Size(totalMeasure.V, totalMeasure.U));
}
/// <inheritdoc />
protected internal override Size ArrangeOverride(VirtualizingLayoutContext context, Size finalSize)
{
if (context.ItemCount > 0)
{
var parentMeasure = new UvMeasure(Orientation, finalSize.Width, finalSize.Height);
var spacingMeasure = new UvMeasure(Orientation, HorizontalSpacing, VerticalSpacing);
var realizationBounds = new UvBounds(Orientation, context.RealizationRect);
var state = (WrapLayoutState)context.LayoutState !;
bool Arrange(WrapItem item, bool isLast = false)
{
if (item.Measure.HasValue == false)
{
return(false);
}
if (item.Position == null)
{
return(false);
}
var desiredMeasure = item.Measure.Value;
if (desiredMeasure.U == 0)
{
return(true); // if an item is collapsed, avoid adding the spacing
}
UvMeasure position = item.Position.Value;
// Stretch the last item to fill the available space
if (isLast)
{
desiredMeasure.U = parentMeasure.U - position.U;
}
if (((position.V + desiredMeasure.V) >= realizationBounds.VMin) && (position.V <= realizationBounds.VMax))
{
// place the item
var child = context.GetOrCreateElementAt(item.Index);
if (Orientation == Orientation.Horizontal)
{
child.Arrange(new Rect(position.U, position.V, desiredMeasure.U, desiredMeasure.V));
}
else
{
child.Arrange(new Rect(position.V, position.U, desiredMeasure.V, desiredMeasure.U));
}
}
else if (position.V > realizationBounds.VMax)
{
return(false);
}
return(true);
}
for (var i = 0; i < context.ItemCount; i++)
{
bool continueArranging = Arrange(state.GetItemAt(i));
if (continueArranging == false)
{
break;
}
}
}
return(finalSize);
}
public void InitializeForContext(VirtualizingLayoutContext context, IFlowLayoutAlgorithmDelegates callbacks)
{
_algorithmCallbacks = callbacks;
_context = context;
_elementManager.SetContext(context);
}
internal void InitializeForContext(VirtualizingLayoutContext context, IFlowLayoutAlgorithmDelegates callbacks)
{
FlowAlgorithm.InitializeForContext(context, callbacks);
context.LayoutState = this;
}
internal void UninitializeForContext(VirtualizingLayoutContext context)
{
FlowAlgorithm.UninitializeForContext(context);
}
internal VirtualizingLayoutContext GetVirtualizingContextAdapter() => _contextAdapter ?? (_contextAdapter = new LayoutContextAdapter(this));
public WrapLayoutState(VirtualizingLayoutContext context)
{
this._context = context;
}
