public ScrollViewer()
{
// put the scroll bars above the presenter and add them to the grid canvas
foreach (var bar in scrollBars)
{
bar.Measure(Vector3.Zero); // set is measure valid to true
VisualChildrenCollection.Add(bar);
SetVisualParent(bar, this);
}
CanBeHitByUser = TouchScrollingEnabled;
ClipToBounds = true;
}
/// <summary>
/// Action to perform when a logical child is added.
/// </summary>
/// <param name="newElement">The element that has been added</param>
/// <param name="index">The index in the collection where the child has been added</param>
protected virtual void OnLogicalChildAdded(UIElement newElement, int index)
{
if (newElement == null)
{
throw new InvalidOperationException("Cannot add a null UIElement to the children list.");
}
SetParent(newElement, this);
SetVisualParent(newElement, this);
VisualChildrenCollection.Sort(PanelChildrenSorter);
if (Children.Count > childrenArrangeWorldMatrix.Length)
{
childrenArrangeWorldMatrix = new Matrix[2 * Children.Count];
}
}
private void UpdateAndArrangeVisibleChildren()
{
var axis = (int)Orientation;
// cache the initial list of children
cachedVisibleChildren.Clear();
foreach (var child in visibleChildren)
{
cachedVisibleChildren.Add(child);
}
// reset the list
visibleChildren.Clear();
// remove all the current visual children
while (VisualChildrenCollection.Count > 0)
{
SetVisualParent(VisualChildrenCollection[0], null);
}
// determine first element index and size
var elementIndex = (int)Math.Floor(scrollPosition);
var firstChildSize = GetSafeChildSize(elementIndex, axis);
// create the next visual children collection to display
var currentSize = -(scrollPosition - elementIndex) * firstChildSize;
while (elementIndex < Children.Count && currentSize <= Viewport[axis])
{
currentSize += GetSafeChildSize(elementIndex, axis);
visibleChildren.Add(Children[elementIndex]);
SetVisualParent(Children[elementIndex], this);
++elementIndex;
}
// reorder visual children by z-Order
VisualChildrenCollection.Sort(PanelChildrenSorter);
// re-arrange the children if they changed
if (visibleChildren.Count > 0)
{
var shouldRearrangeChildren = cachedVisibleChildren.Count == 0 || cachedVisibleChildren.Count != visibleChildren.Count;
// determine if the two list are equals
if (!shouldRearrangeChildren)
{
for (int i = 0; i < visibleChildren.Count; i++)
{
if (cachedVisibleChildren[i] != visibleChildren[i])
{
shouldRearrangeChildren = true;
break;
}
}
}
if (shouldRearrangeChildren)
{
ArrangeChildren();
}
}
}
