public override IEnumerable <FocusNode> sortDescendants(IEnumerable <FocusNode> descendants)
{
FocusTraversalPolicy secondaryPolicy = secondary ?? new ReadingOrderTraversalPolicy();
IEnumerable <FocusNode> sortedDescendants = secondaryPolicy.sortDescendants(descendants);
List <FocusNode> unordered = new List <FocusNode>();
List <_OrderedFocusInfo> ordered = new List <_OrderedFocusInfo>();
foreach (FocusNode node in sortedDescendants)
{
FocusOrder order = FocusTraversalOrder.of(node.context, nullOk: true);
if (order != null)
{
ordered.Add(new _OrderedFocusInfo(node: node, order: order));
}
else
{
unordered.Add(node);
}
}
FocusTravesalUtils.mergeSort <_OrderedFocusInfo>(ordered, compare: (_OrderedFocusInfo a, _OrderedFocusInfo b) => {
D.assert(
a.order.GetType() == b.order.GetType(), () =>
$"When sorting nodes for determining focus order, the order ({a.order}) of " +
$"node {a.node}, isn't the same type as the order ({b.order}) of {b.node}. " +
"Incompatible order types can't be compared. Use a FocusTraversalGroup to group " +
"similar orders together."
);
return(a.order.CompareTo(b.order));
});
return(LinqUtils <FocusNode, _OrderedFocusInfo> .SelectList(ordered, ((_OrderedFocusInfo info) => info.node)).Concat(unordered));
}
public static FocusOrder of(BuildContext context, bool nullOk = false)
{
D.assert(context != null);
FocusTraversalOrder marker = context.getElementForInheritedWidgetOfExactType <FocusTraversalOrder>()?.widget as FocusTraversalOrder;
FocusOrder order = marker?.order;
if (order == null && !nullOk)
{
throw new UIWidgetsError("FocusTraversalOrder.of() was called with a context that " +
"does not contain a TraversalOrder widget. No TraversalOrder widget " +
"ancestor could be found starting from the context that was passed to " +
"FocusTraversalOrder.of().\n" +
"The context used was:\n" +
$" {context}");
}
return(order);
}