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updateChildren() needs to walk the list forward
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This patch changes the framework to walk the child list forwards so that build
functions with global side effects do sensible things. Specifically, if you
have a number of autofocusable children, the first one the list will acquire
the focus because it gets built first now.

Fixes flutter#182
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@abarth
abarth committed Jan 27, 2016
1 parent 594e700 commit 05839e5
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Showing 6 changed files with 118 additions and 118 deletions.
71 changes: 37 additions & 34 deletions packages/flutter/lib/src/rendering/object.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -1294,59 +1294,62 @@ abstract class ContainerRenderObjectMixin<ChildType extends RenderObject, Parent

ChildType _firstChild;
ChildType _lastChild;
void _addToChildList(ChildType child, { ChildType before }) {
void _insertIntoChildList(ChildType child, { ChildType after }) {
final ParentDataType childParentData = child.parentData;
assert(childParentData.nextSibling == null);
assert(childParentData.previousSibling == null);
_childCount += 1;
assert(_childCount > 0);
if (before == null) {
// append at the end (_lastChild)
childParentData.previousSibling = _lastChild;
if (_lastChild != null) {
final ParentDataType _lastChildParentData = _lastChild.parentData;
_lastChildParentData.nextSibling = child;
if (after == null) {
// insert at the start (_firstChild)
childParentData.nextSibling = _firstChild;
if (_firstChild != null) {
final ParentDataType _firstChildParentData = _firstChild.parentData;
_firstChildParentData.previousSibling = child;
}
_lastChild = child;
if (_firstChild == null)
_firstChild = child;
_firstChild = child;
if (_lastChild == null)
_lastChild = child;
} else {
assert(_firstChild != null);
assert(_lastChild != null);
assert(_debugUltimatePreviousSiblingOf(before, equals: _firstChild));
assert(_debugUltimateNextSiblingOf(before, equals: _lastChild));
final ParentDataType beforeParentData = before.parentData;
if (beforeParentData.previousSibling == null) {
// insert at the start (_firstChild); we'll end up with two or more children
assert(before == _firstChild);
childParentData.nextSibling = before;
beforeParentData.previousSibling = child;
_firstChild = child;
assert(_debugUltimatePreviousSiblingOf(after, equals: _firstChild));
assert(_debugUltimateNextSiblingOf(after, equals: _lastChild));
final ParentDataType afterParentData = after.parentData;
if (afterParentData.nextSibling == null) {
// insert at the end (_lastChild); we'll end up with two or more children
assert(after == _lastChild);
childParentData.previousSibling = after;
afterParentData.nextSibling = child;
_lastChild = child;
} else {
// insert in the middle; we'll end up with three or more children
// set up links from child to siblings
childParentData.previousSibling = beforeParentData.previousSibling;
childParentData.nextSibling = before;
childParentData.nextSibling = afterParentData.nextSibling;
childParentData.previousSibling = after;
// set up links from siblings to child
final ParentDataType childPreviousSiblingParentData = childParentData.previousSibling.parentData;
final ParentDataType childNextSiblingParentData = childParentData.nextSibling.parentData;
childPreviousSiblingParentData.nextSibling = child;
childNextSiblingParentData.previousSibling = child;
assert(beforeParentData.previousSibling == child);
assert(afterParentData.nextSibling == child);
}
}
}
/// Insert child into this render object's child list before the given child.
///
/// To insert a child at the end of the child list, omit the before parameter.
void add(ChildType child, { ChildType before }) {
/// Insert child into this render object's child list after the given child.
void insert(ChildType child, { ChildType after }) {
assert(child != this);
assert(before != this);
assert(child != before);
assert(after != this);
assert(child != after);
assert(child != _firstChild);
assert(child != _lastChild);
adoptChild(child);
_addToChildList(child, before: before);
_insertIntoChildList(child, after: after);
}

/// Append child to the end of this render object's child list.
void add(ChildType child) {
insert(child, after: _lastChild);
}

/// Add all the children to the end of this render object's child list.
Expand Down Expand Up @@ -1411,16 +1414,16 @@ abstract class ContainerRenderObjectMixin<ChildType extends RenderObject, Parent
/// More efficient than removing and re-adding the child. Requires the child
/// to already be in the child list at some position. Pass null for before to
/// move the child to the end of the child list.
void move(ChildType child, { ChildType before }) {
void move(ChildType child, { ChildType after }) {
assert(child != this);
assert(before != this);
assert(child != before);
assert(after != this);
assert(child != after);
assert(child.parent == this);
final ParentDataType childParentData = child.parentData;
if (childParentData.nextSibling == before)
if (childParentData.previousSibling == after)
return;
_removeFromChildList(child);
_addToChildList(child, before: before);
_insertIntoChildList(child, after: after);
}

void attach() {
Expand Down
117 changes: 61 additions & 56 deletions packages/flutter/lib/src/widgets/framework.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -1507,79 +1507,80 @@ abstract class RenderObjectElement<T extends RenderObjectWidget> extends Buildab
// Widgets without keys might be synced but there is no guarantee.

// The general approach is to sync the entire new list backwards, as follows:
// 1. Walk the lists from the top until you no longer have
// matching nodes. We don't sync these yet, but we now know to
// skip them below. We do this because at each sync we need to
// pass the pointer to the new next widget as the slot, which
// we can't do until we've synced the next child.
// 2. Walk the lists from the bottom, syncing nodes, until you no
// longer have matching nodes.
// 1. Walk the lists from the top, syncing nodes, until you no longer have
// matching nodes.
// 2. Walk the lists from the bottom, without syncing nodes, until you no
// longer have matching nodes. We'll sync these nodes at the end. We
// don't sync them now because we want to sync all the nodes in order
// from beginning ot end.
// At this point we narrowed the old and new lists to the point
// where the nodes no longer match.
// 3. Walk the narrowed part of the old list to get the list of
// keys and sync null with non-keyed items.
// 4. Walk the narrowed part of the new list backwards:
// 4. Walk the narrowed part of the new list forwards:
// * Sync unkeyed items with null
// * Sync keyed items with the source if it exists, else with null.
// 5. Walk the top list again but backwards, syncing the nodes.
// 5. Walk the bottom of the list again, syncing the nodes.
// 6. Sync null with any items in the list of keys that are still
// mounted.

int childrenTop = 0;
int newChildrenTop = 0;
int oldChildrenTop = 0;
int newChildrenBottom = newWidgets.length - 1;
int oldChildrenBottom = oldChildren.length - 1;

// top of the lists
while ((childrenTop <= oldChildrenBottom) && (childrenTop <= newChildrenBottom)) {
Element oldChild = oldChildren[childrenTop];
Widget newWidget = newWidgets[childrenTop];
List<Element> newChildren = oldChildren.length == newWidgets.length ?
oldChildren : new List<Element>(newWidgets.length);

Element previousChild;

// Update the top of the list.
while ((oldChildrenTop <= oldChildrenBottom) && (newChildrenTop <= newChildrenBottom)) {
Element oldChild = oldChildren[oldChildrenTop];
Widget newWidget = newWidgets[newChildrenTop];
assert(oldChild._debugLifecycleState == _ElementLifecycle.active);
if (!Widget.canUpdate(oldChild.widget, newWidget))
break;
childrenTop += 1;
Element newChild = updateChild(oldChild, newWidget, previousChild);
assert(newChild._debugLifecycleState == _ElementLifecycle.active);
newChildren[newChildrenTop] = newChild;
previousChild = newChild;
newChildrenTop += 1;
oldChildrenTop += 1;
}

List<Element> newChildren = oldChildren.length == newWidgets.length ?
oldChildren : new List<Element>(newWidgets.length);

Element nextSibling;

// bottom of the lists
while ((childrenTop <= oldChildrenBottom) && (childrenTop <= newChildrenBottom)) {
// Scan the bottom of the list.
while ((oldChildrenTop <= oldChildrenBottom) && (newChildrenTop <= newChildrenBottom)) {
Element oldChild = oldChildren[oldChildrenBottom];
Widget newWidget = newWidgets[newChildrenBottom];
assert(oldChild._debugLifecycleState == _ElementLifecycle.active);
if (!Widget.canUpdate(oldChild.widget, newWidget))
break;
Element newChild = updateChild(oldChild, newWidget, nextSibling);
assert(newChild._debugLifecycleState == _ElementLifecycle.active);
newChildren[newChildrenBottom] = newChild;
nextSibling = newChild;
oldChildrenBottom -= 1;
newChildrenBottom -= 1;
}

// middle of the lists - old list
bool haveOldNodes = childrenTop <= oldChildrenBottom;
// Scan the old children in the middle of the list.
bool haveOldChildren = oldChildrenTop <= oldChildrenBottom;
Map<Key, Element> oldKeyedChildren;
if (haveOldNodes) {
if (haveOldChildren) {
oldKeyedChildren = new Map<Key, Element>();
while (childrenTop <= oldChildrenBottom) {
Element oldChild = oldChildren[oldChildrenBottom];
while (oldChildrenTop <= oldChildrenBottom) {
Element oldChild = oldChildren[oldChildrenTop];
assert(oldChild._debugLifecycleState == _ElementLifecycle.active);
if (oldChild.widget.key != null)
oldKeyedChildren[oldChild.widget.key] = oldChild;
else
_deactivateChild(oldChild);
oldChildrenBottom -= 1;
oldChildrenTop += 1;
}
}

// middle of the lists - new list
while (childrenTop <= newChildrenBottom) {
// Update the middle of the list.
while (newChildrenTop <= newChildrenBottom) {
Element oldChild;
Widget newWidget = newWidgets[newChildrenBottom];
if (haveOldNodes) {
Widget newWidget = newWidgets[newChildrenTop];
if (haveOldChildren) {
Key key = newWidget.key;
if (key != null) {
oldChild = oldKeyedChildren[newWidget.key];
Expand All @@ -1596,32 +1597,38 @@ abstract class RenderObjectElement<T extends RenderObjectWidget> extends Buildab
}
}
assert(oldChild == null || Widget.canUpdate(oldChild.widget, newWidget));
Element newChild = updateChild(oldChild, newWidget, nextSibling);
Element newChild = updateChild(oldChild, newWidget, previousChild);
assert(newChild._debugLifecycleState == _ElementLifecycle.active);
assert(oldChild == newChild || oldChild == null || oldChild._debugLifecycleState != _ElementLifecycle.active);
newChildren[newChildrenBottom] = newChild;
nextSibling = newChild;
newChildrenBottom -= 1;
newChildren[newChildrenTop] = newChild;
previousChild = newChild;
newChildrenTop += 1;
}
assert(oldChildrenBottom == newChildrenBottom);
assert(childrenTop == newChildrenBottom + 1);

// now sync the top of the list
while (childrenTop > 0) {
childrenTop -= 1;
Element oldChild = oldChildren[childrenTop];
// We've scaned the whole list.
assert(oldChildrenTop == oldChildrenBottom + 1);
assert(newChildrenTop == newChildrenBottom + 1);
assert(newWidgets.length - newChildrenTop == oldChildren.length - oldChildrenTop);
newChildrenBottom = newWidgets.length - 1;
oldChildrenBottom = oldChildren.length - 1;

// Update the bottom of the list.
while ((oldChildrenTop <= oldChildrenBottom) && (newChildrenTop <= newChildrenBottom)) {
Element oldChild = oldChildren[oldChildrenTop];
assert(oldChild._debugLifecycleState == _ElementLifecycle.active);
Widget newWidget = newWidgets[childrenTop];
Widget newWidget = newWidgets[newChildrenTop];
assert(Widget.canUpdate(oldChild.widget, newWidget));
Element newChild = updateChild(oldChild, newWidget, nextSibling);
Element newChild = updateChild(oldChild, newWidget, previousChild);
assert(newChild._debugLifecycleState == _ElementLifecycle.active);
assert(oldChild == newChild || oldChild == null || oldChild._debugLifecycleState != _ElementLifecycle.active);
newChildren[childrenTop] = newChild;
nextSibling = newChild;
newChildren[newChildrenTop] = newChild;
previousChild = newChild;
newChildrenTop += 1;
oldChildrenTop += 1;
}

// clean up any of the remaining middle nodes from the old list
if (haveOldNodes && !oldKeyedChildren.isEmpty) {
if (haveOldChildren && !oldKeyedChildren.isEmpty) {
for (Element oldChild in oldKeyedChildren.values)
_deactivateChild(oldChild);
}
Expand Down Expand Up @@ -1755,15 +1762,13 @@ class MultiChildRenderObjectElement<T extends MultiChildRenderObjectWidget> exte

void insertChildRenderObject(RenderObject child, Element slot) {
final ContainerRenderObjectMixin renderObject = this.renderObject;
final RenderObject nextSibling = slot?.renderObject;
renderObject.add(child, before: nextSibling);
renderObject.insert(child, after: slot?.renderObject);
assert(renderObject == this.renderObject);
}

void moveChildRenderObject(RenderObject child, dynamic slot) {
final ContainerRenderObjectMixin renderObject = this.renderObject;
final RenderObject nextSibling = slot?.renderObject;
renderObject.move(child, before: nextSibling);
renderObject.move(child, after: slot?.renderObject);
assert(renderObject == this.renderObject);
}

Expand Down Expand Up @@ -1797,7 +1802,7 @@ class MultiChildRenderObjectElement<T extends MultiChildRenderObjectWidget> exte
super.mount(parent, newSlot);
_children = new List<Element>(widget.children.length);
Element previousChild;
for (int i = _children.length - 1; i >= 0; --i) {
for (int i = 0; i < _children.length; ++i) {
Element newChild = _inflateWidget(widget.children[i], previousChild);
_children[i] = newChild;
previousChild = newChild;
Expand Down
6 changes: 2 additions & 4 deletions packages/flutter/lib/src/widgets/homogeneous_viewport.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -118,14 +118,12 @@ abstract class _ViewportBaseElement<T extends _ViewportBase> extends RenderObjec
}

void insertChildRenderObject(RenderObject child, Element slot) {
RenderObject nextSibling = slot?.renderObject;
renderObject.add(child, before: nextSibling);
renderObject.insert(child, after: slot?.renderObject);
}

void moveChildRenderObject(RenderObject child, Element slot) {
assert(child.parent == renderObject);
RenderObject nextSibling = slot?.renderObject;
renderObject.move(child, before: nextSibling);
renderObject.move(child, after: slot?.renderObject);
}

void removeChildRenderObject(RenderObject child) {
Expand Down
25 changes: 11 additions & 14 deletions packages/flutter/lib/src/widgets/mixed_viewport.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -552,14 +552,12 @@ class _MixedViewportElement extends RenderObjectElement<MixedViewport> {
if (haveChildren) {
// Place all our children in our RenderObject.
// All the children we are placing are in builtChildren and newChildren.
// We will walk them backwards so we can set the slots at the same time.
Element nextSibling = null;
while (index > startIndex) {
index -= 1;
final Element element = builtChildren[index];
if (element.slot != nextSibling)
updateSlotForChild(element, nextSibling);
nextSibling = element;
Element previousChild = null;
for (int i = startIndex; i < index; ++i) {
final Element element = builtChildren[i];
if (element.slot != previousChild)
updateSlotForChild(element, previousChild);
previousChild = element;
}
}

Expand All @@ -577,20 +575,19 @@ class _MixedViewportElement extends RenderObjectElement<MixedViewport> {
if (slot == _omit)
return;
assert(slot == null || slot is Element);
RenderObject nextSibling = slot?.renderObject;
renderObject.add(child, before: nextSibling);
renderObject.insert(child, after: slot?.renderObject);
}

void moveChildRenderObject(RenderObject child, dynamic slot) {
if (slot == _omit)
return;
assert(slot == null || slot is Element);
RenderObject nextSibling = slot?.renderObject;
assert(nextSibling == null || nextSibling.parent == renderObject);
RenderObject previousSibling = slot?.renderObject;
assert(previousSibling == null || previousSibling.parent == renderObject);
if (child.parent == renderObject)
renderObject.move(child, before: nextSibling);
renderObject.move(child, after: previousSibling);
else
renderObject.add(child, before: nextSibling);
renderObject.insert(child, after: previousSibling);
}

void removeChildRenderObject(RenderObject child) {
Expand Down
6 changes: 2 additions & 4 deletions packages/flutter/lib/src/widgets/virtual_viewport.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -149,14 +149,12 @@ abstract class VirtualViewportElement<T extends VirtualViewport> extends RenderO
}

void insertChildRenderObject(RenderObject child, Element slot) {
RenderObject nextSibling = slot?.renderObject;
renderObject.add(child, before: nextSibling);
renderObject.insert(child, after: slot?.renderObject);
}

void moveChildRenderObject(RenderObject child, Element slot) {
assert(child.parent == renderObject);
RenderObject nextSibling = slot?.renderObject;
renderObject.move(child, before: nextSibling);
renderObject.move(child, after: slot?.renderObject);
}

void removeChildRenderObject(RenderObject child) {
Expand Down
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