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Provide a fast path for MultiChildRenderObjectWrapper.syncRenderObject() when the children lists are identical.

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This isn't so much for performance so much as because I don't want to
have to keep checking that the main syncChildren() function maintains
the invariant of not screwing up when the two lists are actually the
same list.
This commit is contained in:
Hixie 2015-08-27 14:49:29 -07:00
parent 338ca571b2
commit 204c073615
1 changed files with 16 additions and 1 deletions
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17
packages/flutter/lib/widgets/framework.dart
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@ -1001,6 +1001,9 @@ abstract class RenderObjectWrapper extends Widget {
// for use by subclasses that manage their children using lists
void syncChildren(List<Widget> newChildren, List<Widget> oldChildren) {
assert(newChildren != null);
assert(oldChildren != null);
assert(!identical(newChildren, oldChildren));
// This attempts to diff the new child list (this.children) with
// the old child list (old.children), and update our renderObject
@ -1260,7 +1263,19 @@ abstract class MultiChildRenderObjectWrapper extends RenderObjectWrapper {
void syncRenderObject(MultiChildRenderObjectWrapper old) {
super.syncRenderObject(old);
syncChildren(children, old == null ? const <Widget>[] : old.children);
List<Widget> oldChildren = old == null ? const <Widget>[] : old.children;
if (oldChildren == children) {
int index = children.length;
Widget nextSibling = null;
while (index > 0) {
index -= 1;
Widget child = children[index];
nextSibling = syncChild(child, child, nextSibling);
children[index] = nextSibling;
}
} else {
syncChildren(children, oldChildren);
}
}
}