Added SliverPrototypeExtentList et al (#10097)

packages/flutter/lib/src/rendering/sliver_fixed_extent_list.dart

@@ -28,6 +28,8 @@ import 'sliver_multi_box_adaptor.dart';
 /// See also:
 ///
 ///  * [RenderSliverFixedExtentList], which has a configurable [itemExtent].
+///  * [RenderSliverPrototypeExtentList], which uses a prototype list item
+///    instead of a pixel value, to define the extent of each item.
 ///  * [RenderSliverFillViewport], which determines the [itemExtent] based on
 ///    [SliverConstraints.viewportMainAxisExtent].
 ///  * [RenderSliverFillRemaining], which determines the [itemExtent] based on
@@ -231,6 +233,8 @@ abstract class RenderSliverFixedExtentBoxAdaptor extends RenderSliverMultiBoxAda
 ///
 /// See also:
 ///
+///  * [RenderSliverPrototypeExtentList], which uses a prototype list item
+///    instead of a pixel value, to define the extent of each item.
 ///  * [RenderSliverList], which does not require its children to have the same
 ///    extent in the main axis.
 ///  * [RenderSliverFillViewport], which determines the [itemExtent] based on

packages/flutter/lib/src/widgets/basic.dart

@@ -1557,9 +1557,9 @@ class Baseline extends SingleChildRenderObjectWidget {
 ///
 /// Rather than using multiple [SliverToBoxAdapter] widgets to display multiple
 /// box widgets in a [CustomScrollView], consider using [SliverList],
-/// [SliverFixedExtentList], or [SliverGrid], which are more efficient because
-/// they instantiate only those children that are actually visible through the
-/// scroll view's viewport.
+/// [SliverFixedExtentList], [SliverPrototypeExtentList], or [SliverGrid],
+/// which are more efficient because they instantiate only those children that
+/// are actually visible through the scroll view's viewport.
 ///
 /// See also:
 ///
@@ -1567,6 +1567,8 @@ class Baseline extends SingleChildRenderObjectWidget {
 ///  * [SliverList], which displays multiple box widgets in a linear array.
 ///  * [SliverFixedExtentList], which displays multiple box widgets with the
 ///    same main-axis extent in a linear array.
+///  * [SliverPrototypeExtentList], which displays multiple box widgets with the
+///    same main-axis extent as a prototype item, in a linear array.
 ///  * [SliverGrid], which displays multiple box widgets in arbitrary positions.
 class SliverToBoxAdapter extends SingleChildRenderObjectWidget {
   /// Creates a sliver that contains a single box widget.

packages/flutter/lib/src/widgets/sliver.dart

@@ -304,6 +304,9 @@ abstract class SliverMultiBoxAdaptorWidget extends RenderObjectWidget {
 ///
 ///  * [SliverFixedExtentList], which is more efficient for children with
 ///    the same extent in the main axis.
+///  * [SliverPrototypeExtentList], which is similar to [SliverFixedExtentList]
+///    except that it uses a prototype list item intead a pixel value to define
+///    the main axis extent of each item.
 ///  * [SliverGrid], which places its children in arbitrary positions.
 class SliverList extends SliverMultiBoxAdaptorWidget {
   /// Creates a sliver that places box children in a linear array.
@@ -333,6 +336,9 @@ class SliverList extends SliverMultiBoxAdaptorWidget {
 ///
 /// See also:
 ///
+///  * [SliverPrototypeExtentList], which is similar to [SliverFixedExtentList]
+///    except that it uses a prototype list item intead a pixel value to define
+///    the main axis extent of each item.
 ///  * [SliverFillViewport], which determines the [itemExtent] based on
 ///    [SliverConstraints.viewportMainAxisExtent].
 ///  * [SliverList], which does not require its children to have the same
@@ -372,6 +378,9 @@ class SliverFixedExtentList extends SliverMultiBoxAdaptorWidget {
 ///  * [SliverList], which places its children in a linear array.
 ///  * [SliverFixedExtentList], which places its children in a linear
 ///    array with a fixed extent in the main axis.
+///  * [SliverPrototypeExtentList], which is similar to [SliverFixedExtentList]
+///    except that it uses a prototype list item intead a pixel value to define
+///    the main axis extent of each item.
 class SliverGrid extends SliverMultiBoxAdaptorWidget {
   /// Creates a sliver that places multiple box children in a two dimensional
   /// arrangement.
@@ -423,6 +432,9 @@ class SliverGrid extends SliverMultiBoxAdaptorWidget {
 ///
 ///  * [SliverFixedExtentList], which has a configurable
 ///    [SliverFixedExtentList.itemExtent].
+///  * [SliverPrototypeExtentList], which is similar to [SliverFixedExtentList]
+///    except that it uses a prototype list item intead a pixel value to define
+///    the main axis extent of each item.
 ///  * [SliverList], which does not require its children to have the same
 ///    extent in the main axis.
 class SliverFillViewport extends SliverMultiBoxAdaptorWidget {
@@ -469,7 +481,7 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
   RenderSliverMultiBoxAdaptor get renderObject => super.renderObject;
 
   @override
-  void update(SliverMultiBoxAdaptorWidget newWidget) {
+  void update(covariant SliverMultiBoxAdaptorWidget newWidget) {
     final SliverMultiBoxAdaptorWidget oldWidget = widget;
     super.update(newWidget);
     final SliverChildDelegate newDelegate = newWidget.delegate;

packages/flutter/lib/src/widgets/sliver_prototype_item_list.dart

@@ -0,0 +1,183 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/rendering.dart';
+
+import 'basic.dart';
+import 'framework.dart';
+import 'sliver.dart';
+
+/// A sliver that places its box children in a linear array and constrains them
+/// to have the same extent as a prototype item along the main axis.
+///
+/// [SliverPrototypeExtentList] arranges its children in a line along
+/// the main axis starting at offset zero and without gaps. Each child is
+/// constrained to the same extent as the [prototypeItem] along the main axis
+/// and the [SliverConstraints.crossAxisExtent] along the cross axis.
+///
+/// [SliverPrototypeExtentList] is more efficient than [SliverList] because
+/// [SliverPrototypeExtentList] does not need to lay out its children to obtain
+/// their extent along the main axis. It's a little more flexible than
+/// [SliverFixedExtentList] because there's no need to determine the approriate
+/// item extent in pixels.
+///
+/// See also:
+///
+///  * [SliverFixedExtentList], whose [itemExtent] is a pixel value.
+///  * [SliverList], which does not require its children to have the same
+///    extent in the main axis.
+///  * [SliverFillViewport], which sizes its children based on the
+///    size of the viewport, regardless of what else is in the scroll view.
+///  * [SliverList], which shows a list of variable-sized children in a
+///    viewport.
+class SliverPrototypeExtentList extends SliverMultiBoxAdaptorWidget {
+  /// Creates a sliver that places its box children in a linear array and
+  /// constrains them to have the same extent as a prototype item along
+  /// the main axis.
+  const SliverPrototypeExtentList({
+    Key key,
+    @required SliverChildDelegate delegate,
+    @required this.prototypeItem,
+  }) : assert(prototypeItem != null), super(key: key, delegate: delegate);
+
+  /// Defines the main axis extent of all of this sliver's children.
+  ///
+  /// The [prototypeItem] is laid out before the rest of the sliver's children
+  /// and its size along the main axis fixes the size of each child. The
+  /// [prototypeItem] is essentially [Offstage]: it is not painted and it
+  /// cannot respond to input.
+  final Widget prototypeItem;
+
+  @override
+  _RenderSliverPrototypeExtentList createRenderObject(BuildContext context) {
+    final _SliverPrototypeExtentListElement element = context;
+    return new _RenderSliverPrototypeExtentList(childManager: element);
+  }
+
+  @override
+  _SliverPrototypeExtentListElement createElement() => new _SliverPrototypeExtentListElement(this);
+}
+
+class _SliverPrototypeExtentListElement extends SliverMultiBoxAdaptorElement {
+  _SliverPrototypeExtentListElement(SliverPrototypeExtentList widget) : super(widget);
+
+  @override
+  SliverPrototypeExtentList get widget => super.widget;
+
+  @override
+  _RenderSliverPrototypeExtentList get renderObject => super.renderObject;
+
+  Element _prototype;
+  static final Object _prototypeSlot = new Object();
+
+  @override
+  void insertChildRenderObject(covariant RenderObject child, covariant dynamic slot) {
+    if (slot == _prototypeSlot) {
+      assert(child is RenderBox);
+      renderObject.child = child;
+    } else {
+      super.insertChildRenderObject(child, slot);
+    }
+  }
+
+  @override
+  void didAdoptChild(RenderBox child) {
+    if (child != renderObject.child)
+      super.didAdoptChild(child);
+  }
+
+  @override
+  void moveChildRenderObject(RenderBox child, dynamic slot) {
+    if (slot == _prototypeSlot)
+      assert(false); // There's only one prototype child so it cannot be moved.
+    else
+      super.moveChildRenderObject(child, slot);
+  }
+
+  @override
+  void removeChildRenderObject(RenderBox child) {
+    if (renderObject.child == child)
+      renderObject.child = null;
+    else
+      super.removeChildRenderObject(child);
+  }
+
+  @override
+  void visitChildren(ElementVisitor visitor) {
+    if (_prototype != null)
+      visitor(_prototype);
+    super.visitChildren(visitor);
+  }
+
+  @override
+  void mount(Element parent, dynamic newSlot) {
+    super.mount(parent, newSlot);
+    _prototype = updateChild(_prototype, widget.prototypeItem, _prototypeSlot);
+  }
+
+  @override
+  void update(SliverPrototypeExtentList newWidget) {
+    super.update(newWidget);
+    assert(widget == newWidget);
+    _prototype = updateChild(_prototype, widget.prototypeItem, _prototypeSlot);
+  }
+}
+
+class _RenderSliverPrototypeExtentList extends RenderSliverFixedExtentBoxAdaptor {
+  _RenderSliverPrototypeExtentList({
+    @required _SliverPrototypeExtentListElement childManager,
+  }) : super(childManager: childManager);
+
+  RenderBox _child;
+  RenderBox get child => _child;
+  set child(RenderBox value) {
+    if (_child != null)
+      dropChild(_child);
+    _child = value;
+    if (_child != null)
+      adoptChild(_child);
+    markNeedsLayout();
+  }
+
+  @override
+  void performLayout() {
+    child.layout(constraints.asBoxConstraints(), parentUsesSize: true);
+    super.performLayout();
+  }
+
+  @override
+  void attach(PipelineOwner owner) {
+    super.attach(owner);
+    if (_child != null)
+      _child.attach(owner);
+  }
+
+  @override
+  void detach() {
+    super.detach();
+    if (_child != null)
+      _child.detach();
+  }
+
+  @override
+  void redepthChildren() {
+    if (_child != null)
+      redepthChild(_child);
+    super.redepthChildren();
+  }
+
+  @override
+  void visitChildren(RenderObjectVisitor visitor) {
+    if (_child != null)
+      visitor(_child);
+    super.visitChildren(visitor);
+  }
+
+  @override
+  double get itemExtent {
+    assert(child != null && child.hasSize);
+    return constraints.axis == Axis.vertical ? child.size.height : child.size.width;
+  }
+}

packages/flutter/lib/widgets.dart

@@ -72,6 +72,7 @@ export 'src/widgets/single_child_scroll_view.dart';
 export 'src/widgets/size_changed_layout_notifier.dart';
 export 'src/widgets/sliver.dart';
 export 'src/widgets/sliver_persistent_header.dart';
+export 'src/widgets/sliver_prototype_item_list.dart';
 export 'src/widgets/status_transitions.dart';
 export 'src/widgets/table.dart';
 export 'src/widgets/text.dart';

packages/flutter/test/widgets/sliver_prototype_item_extent_test.dart

@@ -0,0 +1,133 @@
+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/widgets.dart';
+
+class TestItem extends StatelessWidget {
+  const TestItem({ Key key, this.item, this.width, this.height }) : super(key: key);
+  final int item;
+  final double width;
+  final double height;
+  @override
+  Widget build(BuildContext context) {
+    return new Container(
+      width: width,
+      height: height,
+      alignment: FractionalOffset.center,
+      child: new Text('Item $item'),
+    );
+  }
+}
+
+Widget buildFrame({ int count, double width, double height, Axis scrollDirection }) {
+  return new CustomScrollView(
+    scrollDirection: scrollDirection ?? Axis.vertical,
+    slivers: <Widget>[
+      new SliverPrototypeExtentList(
+        prototypeItem: new TestItem(item: -1, width: width, height: height),
+        delegate: new SliverChildBuilderDelegate(
+          (BuildContext context, int index) => new TestItem(item: index),
+          childCount: count,
+        ),
+      ),
+    ],
+  );
+}
+
+void main() {
+  testWidgets('SliverPrototypeExtentList vertical scrolling basics', (WidgetTester tester) async {
+    await tester.pumpWidget(buildFrame(count: 20, height: 100.0));
+
+    // The viewport is 600 pixels high, lazily created items are 100 pixels high.
+    for (int i = 0; i < 6; i += 1) {
+      final Finder item = find.widgetWithText(Container, 'Item $i');
+      expect(item, findsOneWidget);
+      expect(tester.getTopLeft(item).dy, i * 100.0);
+      expect(tester.getSize(item).height, 100.0);
+    }
+    for (int i = 7; i < 20; i += 1)
+      expect(find.text('Item $i'), findsNothing);
+
+    // Fling scroll to the end.
+    await tester.fling(find.text('Item 2'), const Offset(0.0, -200.0), 5000.0);
+    await tester.pumpAndSettle();
+
+    for (int i = 19; i >= 14; i -= 1)
+      expect(find.text('Item $i'), findsOneWidget);
+    for (int i = 13; i >= 0; i -= 1)
+      expect(find.text('Item $i'), findsNothing);
+  });
+
+  testWidgets('SliverPrototypeExtentList horizontal scrolling basics', (WidgetTester tester) async {
+    await tester.pumpWidget(buildFrame(count: 20, width: 100.0, scrollDirection: Axis.horizontal));
+
+    // The viewport is 800 pixels wide, lazily created items are 100 pixels wide.
+    for (int i = 0; i < 8; i += 1) {
+      final Finder item = find.widgetWithText(Container, 'Item $i');
+      expect(item, findsOneWidget);
+      expect(tester.getTopLeft(item).dx, i * 100.0);
+      expect(tester.getSize(item).width, 100.0);
+    }
+    for (int i = 9; i < 20; i += 1)
+      expect(find.text('Item $i'), findsNothing);
+
+    // Fling scroll to the end.
+    await tester.fling(find.text('Item 3'), const Offset(-200.0, 0.0), 5000.0);
+    await tester.pumpAndSettle();
+
+    for (int i = 19; i >= 12; i -= 1)
+      expect(find.text('Item $i'), findsOneWidget);
+    for (int i = 11; i >= 0; i -= 1)
+      expect(find.text('Item $i'), findsNothing);
+  });
+
+  testWidgets('SliverPrototypeExtentList change the prototype item', (WidgetTester tester) async {
+    await tester.pumpWidget(buildFrame(count: 10, height: 60.0));
+
+    // The viewport is 600 pixels high, each of the 10 items is 60 pixels high
+    for (int i = 0; i < 10; i += 1)
+      expect(find.text('Item $i'), findsOneWidget);
+
+    await tester.pumpWidget(buildFrame(count: 10, height: 120.0));
+
+    // Now the items are 120 pixels high, so only 5 fit.
+    for (int i = 0; i < 5; i += 1)
+      expect(find.text('Item $i'), findsOneWidget);
+    for (int i = 5; i < 10; i += 1)
+      expect(find.text('Item $i'), findsNothing);
+
+    await tester.pumpWidget(buildFrame(count: 10, height: 60.0));
+
+    // Now they all fit again
+    for (int i = 0; i < 10; i += 1)
+      expect(find.text('Item $i'), findsOneWidget);
+  });
+
+  testWidgets('SliverPrototypeExtentList first item is also the prototype', (WidgetTester tester) async {
+    final List<Widget> items = new List<Widget>.generate(10, (int index) {
+      return new TestItem(key: new ValueKey<int>(index), item: index, height: index == 0 ? 60.0 : null);
+    }).toList();
+
+    await tester.pumpWidget(
+      new CustomScrollView(
+        slivers: <Widget>[
+          new SliverPrototypeExtentList(
+            prototypeItem: items[0],
+            delegate: new SliverChildBuilderDelegate(
+              (BuildContext context, int index) => items[index],
+              childCount: 10,
+            ),
+          ),
+        ],
+      )
+    );
+
+    // Item 0 exists in the list and as the prototype item.
+    expect(tester.widgetList(find.text('Item 0')).length, 2);
+
+    for (int i = 1; i < 10; i += 1)
+      expect(find.text('Item $i'), findsOneWidget);
+  });
+}