/// <summary>
/// Get the range of children that are visible
/// </summary>
/// <param name="firstVisibleItemIndex">The item index of the first visible item</param>
/// <param name="lastVisibleItemIndex">The item index of the last visible item</param>
private VisibleRange GetVisibleRange()
{
ItemsControl itemsControl = ItemsControl.GetItemsOwner(this);
int itemCount = itemsControl.HasItems ? itemsControl.Items.Count : 0;
if (itemCount == 0)
{
return VisibleRange.Empty;
}
else {
int columns = DataSource.Source.Columns.Length;
VisibleRange range = new VisibleRange();
range.firstRow = Math.Max(0,(int)Math.Floor(_offset.Y / PropertiesGridControl.RowHeight) - CREATE_MARGIN_ELEMENTS);
range.firstCol = (int)Math.Floor(_offset.X / PropertiesGridControl.DataItemWidth);
range.rowCount = (int)Math.Ceiling((_viewport.Height) / PropertiesGridControl.RowHeight) + (CREATE_MARGIN_ELEMENTS*2) + 1; //Anstatt +1 wäre korrekterweise der ausgeblendete Teil der ersten Zeile zu beachten
range.colCount = Math.Min(columns-range.firstCol,(int)Math.Ceiling((_viewport.Width) / PropertiesGridControl.DataItemWidth) + 1); //--||--
int lastIndex = (range.firstRow + range.rowCount) * columns + range.firstCol + range.colCount;
if (lastIndex >= itemCount)
{
//Anzeige kann nicht komplett ausgefüllt werden
int maxRowCount = Math.Max(0, itemCount / columns - range.firstRow);
range.rowCount = Math.Min(maxRowCount, range.rowCount);
}
return range;
}
}
/// <summary>
/// Revirtualize items that are no longer visible
/// </summary>
private void CleanUpItems(VisibleRange visibleRange, int columCount)
{
UIElementCollection children = this.InternalChildren;
if (children.Count > 0)
{
ItemsControl itemsControl = ItemsControl.GetItemsOwner(this);
IItemContainerGenerator generator = this.ItemContainerGenerator;
int firstVisibleIndex = visibleRange.firstRow * columCount + visibleRange.firstCol;
int lastVisibleIndex = (visibleRange.firstRow + visibleRange.rowCount) * columCount + visibleRange.firstCol + visibleRange.colCount;
for (int i = children.Count - 1; i >= 0; i--)
{
GeneratorPosition childGeneratorPos = new GeneratorPosition(i, 0);
int itemIndex = generator.IndexFromGeneratorPosition(childGeneratorPos);
if (itemIndex < firstVisibleIndex || itemIndex > lastVisibleIndex)
{
if (!((ItemViewModel)itemsControl.Items.GetItemAt(itemIndex)).InEditMode)
{
generator.Remove(childGeneratorPos, 1);
RemoveInternalChildRange(i, 1);
}
}
}
}
}
protected override Size MeasureOverride(Size availableSize)
{
UpdateScrollInfo(availableSize);
// Figure out range that's visible based on layout algorithm
VisibleRange visibleRange = GetVisibleRange();
_prevVisibleRange = visibleRange;
if (SCROLL_CREATE_ITEMS_DELAY_MS == 0)
{
CalculateChildren(visibleRange);
}
else
{
Task.Delay(SCROLL_CREATE_ITEMS_DELAY_MS).ContinueWith((t) =>
{
//Wartet für die angegeben Zeitspanne
//Falls sich der angezeigte Bereich in dieser Zeit nicht geändert hat
// -> Child-Element erzeugen
if (visibleRange.Equals(_prevVisibleRange) && !visibleRange.Equals(_calculatedVisibleRange))
{
_calculatedVisibleRange = visibleRange;
CalculateChildren(visibleRange);
}
}, TaskScheduler.FromCurrentSynchronizationContext());
}
return availableSize;
}
private void CalculateChildren(VisibleRange visibleRange)
{
// We need to access InternalChildren before the generator to work around a bug
UIElementCollection children = this.InternalChildren;
IItemContainerGenerator generator = this.ItemContainerGenerator;
int columCount = DataSource.Source.Columns.Length;
ItemsControl itemsControl = ItemsControl.GetItemsOwner(this);
int lastRow = visibleRange.firstRow + visibleRange.rowCount;
for (int r = visibleRange.firstRow; r < lastRow; r++)
{
int firstVisibleItemInRow = r * columCount + visibleRange.firstCol;
int lastVisibleItemInRow = firstVisibleItemInRow + visibleRange.colCount - 1;
GeneratorPosition startPos = generator.GeneratorPositionFromIndex(firstVisibleItemInRow);
// Get index where we'd insert the child for this position. If the item is realized
// (position.Offset == 0), it's just position.Index, otherwise we have to add one to
// insert after the corresponding child
int childIndex = (startPos.Offset == 0) ? startPos.Index : startPos.Index + 1;
using (generator.StartAt(startPos, GeneratorDirection.Forward, true))
{
for (int itemIndex = firstVisibleItemInRow; itemIndex <= lastVisibleItemInRow; ++itemIndex, ++childIndex)
{
if (((ItemViewModel)itemsControl.Items[itemIndex]).Item != null)
{
bool newlyRealized;
// Get or create the child
UIElement child = generator.GenerateNext(out newlyRealized) as UIElement;
if (newlyRealized)
{
// Figure out if we need to insert the child at the end or somewhere in the middle
if (childIndex >= children.Count)
{
base.AddInternalChild(child);
}
else
{
base.InsertInternalChild(childIndex, child);
}
generator.PrepareItemContainer(child);
this.DataSource.HoverManager.RegisterItem(child);
}
else
{
// The child has already been created, let's be sure it's in the right spot
//Debug.Assert(child == children[childIndex], "Wrong child was generated");
}
// Measurements will depend on layout algorithm
if (child != null)
child.Measure(GetChildSize());
}
}
}
}
// Note: this could be deferred to idle time for efficiency
CleanUpItems(visibleRange, columCount);
}
public void Refresh()
{
_calculatedVisibleRange = VisibleRange.Empty;
}