Add SliverFill (#7776)

SliverFill fills the remaining space in the viewport with each box
child. We'll use this sliver as a building block for pageable lists.

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

@@ -10,30 +10,21 @@ import 'box.dart';
 import 'sliver.dart';
 import 'sliver_multi_box_adaptor.dart';
 
-class RenderSliverList extends RenderSliverMultiBoxAdaptor {
-  RenderSliverList({
+abstract class RenderSliverFixedExtentBoxAdaptor extends RenderSliverMultiBoxAdaptor {
+  RenderSliverFixedExtentBoxAdaptor({
     @required RenderSliverBoxChildManager childManager,
-    double itemExtent,
-  }) : _itemExtent = itemExtent, super(childManager: childManager) {
-    assert(itemExtent != null);
-  }
-
-  /// The main-axis extent of each item in the list.
-  double get itemExtent => _itemExtent;
-  double _itemExtent;
-  set itemExtent (double newValue) {
-    assert(newValue != null);
-    if (_itemExtent == newValue)
-      return;
-    _itemExtent = newValue;
-    markNeedsLayout();
-  }
+  }) : super(childManager: childManager);
 
-  double _indexToScrollOffset(int index) => _itemExtent * index;
+  /// The main-axis extent of each item.
+  double get itemExtent;
 
   @override
   void performLayout() {
     assert(childManager.debugAssertChildListLocked());
+
+    final double itemExtent = this.itemExtent;
+    double indexToScrollOffset(int index) => itemExtent * index;
+
     final double scrollOffset = constraints.scrollOffset;
     assert(scrollOffset >= 0.0);
     final double remainingPaintExtent = constraints.remainingPaintExtent;
@@ -45,8 +36,8 @@ class RenderSliverList extends RenderSliverMultiBoxAdaptor {
       maxExtent: itemExtent,
     );
 
-    final int firstIndex = math.max(0, scrollOffset ~/ _itemExtent);
-    final int targetLastIndex = math.max(0, (targetEndScrollOffset / itemExtent).ceil());
+    final int firstIndex = math.max(0, scrollOffset ~/ itemExtent);
+    final int targetLastIndex = math.max(0, (targetEndScrollOffset / itemExtent).ceil() - 1);
 
     if (firstChild != null) {
       final int oldFirstIndex = indexOf(firstChild);
@@ -58,7 +49,7 @@ class RenderSliverList extends RenderSliverMultiBoxAdaptor {
     }
 
     if (firstChild == null) {
-      if (!addInitialChild(index: firstIndex, scrollOffset: _indexToScrollOffset(firstIndex))) {
+      if (!addInitialChild(index: firstIndex, scrollOffset: indexToScrollOffset(firstIndex))) {
         // There are no children.
         geometry = SliverGeometry.zero;
         return;
@@ -70,7 +61,7 @@ class RenderSliverList extends RenderSliverMultiBoxAdaptor {
     for (int index = indexOf(firstChild) - 1; index >= firstIndex; --index) {
       final RenderBox child = insertAndLayoutLeadingChild(childConstraints);
       final SliverMultiBoxAdaptorParentData childParentData = child.parentData;
-      childParentData.scrollOffset = _indexToScrollOffset(index);
+      childParentData.scrollOffset = indexToScrollOffset(index);
       assert(childParentData.index == index);
       trailingChildWithLayout ??= child;
     }
@@ -96,12 +87,12 @@ class RenderSliverList extends RenderSliverMultiBoxAdaptor {
       trailingChildWithLayout = child;
       assert(child != null);
       final SliverMultiBoxAdaptorParentData childParentData = child.parentData;
-      childParentData.scrollOffset = _indexToScrollOffset(childParentData.index);
+      childParentData.scrollOffset = indexToScrollOffset(childParentData.index);
     }
 
     final int lastIndex = indexOf(lastChild);
-    final double leadingScrollOffset = _indexToScrollOffset(firstIndex);
-    final double trailingScrollOffset = _indexToScrollOffset(lastIndex + 1);
+    final double leadingScrollOffset = indexToScrollOffset(firstIndex);
+    final double trailingScrollOffset = indexToScrollOffset(lastIndex + 1);
 
     assert(debugAssertChildListIsNonEmptyAndContiguous());
     assert(indexOf(firstChild) == firstIndex);
@@ -132,3 +123,30 @@ class RenderSliverList extends RenderSliverMultiBoxAdaptor {
     assert(childManager.debugAssertChildListLocked());
   }
 }
+
+class RenderSliverList extends RenderSliverFixedExtentBoxAdaptor {
+  RenderSliverList({
+    @required RenderSliverBoxChildManager childManager,
+    double itemExtent,
+  }) : _itemExtent = itemExtent, super(childManager: childManager);
+
+  @override
+  double get itemExtent => _itemExtent;
+  double _itemExtent;
+  set itemExtent (double newValue) {
+    assert(newValue != null);
+    if (_itemExtent == newValue)
+      return;
+    _itemExtent = newValue;
+    markNeedsLayout();
+  }
+}
+
+class RenderSliverFill extends RenderSliverFixedExtentBoxAdaptor {
+  RenderSliverFill({
+    @required RenderSliverBoxChildManager childManager,
+  }) : super(childManager: childManager);
+
+  @override
+  double get itemExtent => constraints.remainingPaintExtent;
+}

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

@@ -188,6 +188,19 @@ class SliverGrid extends SliverMultiBoxAdaptorWidget {
   }
 }
 
+class SliverFill extends SliverMultiBoxAdaptorWidget {
+  SliverFill({
+    Key key,
+    @required SliverChildDelegate delegate,
+  }) : super(key: key, delegate: delegate);
+
+  @override
+  RenderSliverFill createRenderObject(BuildContext context) {
+    final SliverMultiBoxAdaptorElement element = context;
+    return new RenderSliverFill(childManager: element);
+  }
+}
+
 class SliverMultiBoxAdaptorElement extends RenderObjectElement implements RenderSliverBoxChildManager {
   SliverMultiBoxAdaptorElement(SliverMultiBoxAdaptorWidget widget) : super(widget);
 

packages/flutter/test/widgets/list_test.dart

@@ -24,7 +24,7 @@ void main() {
     expect(find.text('0'), findsOneWidget);
     expect(find.text('1'), findsOneWidget);
     expect(find.text('2'), findsOneWidget);
-    expect(find.text('3'), findsOneWidget);
+    expect(find.text('3'), findsNothing);
     expect(find.text('4'), findsNothing);
 
     await tester.scroll(find.byType(ScrollView), const Offset(0.0, -250.0));
@@ -35,7 +35,7 @@ void main() {
     expect(find.text('2'), findsOneWidget);
     expect(find.text('3'), findsOneWidget);
     expect(find.text('4'), findsOneWidget);
-    expect(find.text('5'), findsOneWidget);
+    expect(find.text('5'), findsNothing);
     expect(find.text('6'), findsNothing);
 
     await tester.scroll(find.byType(ScrollView), const Offset(0.0, 200.0));
@@ -45,7 +45,7 @@ void main() {
     expect(find.text('1'), findsOneWidget);
     expect(find.text('2'), findsOneWidget);
     expect(find.text('3'), findsOneWidget);
-    expect(find.text('4'), findsOneWidget);
+    expect(find.text('4'), findsNothing);
     expect(find.text('5'), findsNothing);
   });
 
@@ -68,7 +68,7 @@ void main() {
       ),
     );
 
-    expect(log, equals(<int>[0, 1, 2, 3]));
+    expect(log, equals(<int>[0, 1, 2]));
     log.clear();
 
     Scrollable2State state = tester.state(find.byType(Scrollable2));
@@ -78,7 +78,7 @@ void main() {
     expect(log, isEmpty);
     await tester.pump();
 
-    expect(log, equals(<int>[10, 11, 12, 13, 14]));
+    expect(log, equals(<int>[10, 11, 12, 13]));
     log.clear();
 
     position.jumpTo(975.0);
@@ -86,7 +86,7 @@ void main() {
     expect(log, isEmpty);
     await tester.pump();
 
-    expect(log, equals(<int>[4, 5, 6, 7, 8]));
+    expect(log, equals(<int>[4, 5, 6, 7]));
     log.clear();
   });
 }

packages/flutter/test/widgets/sliver_fill_remaining_test.dart

+// 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';
+
+void main() {
+  testWidgets('SliverFillRemaining control test', (WidgetTester tester) async {
+    List<Widget> children = new List<Widget>.generate(20, (int i) {
+      return new Container(child: new Text('$i'));
+    });
+
+    await tester.pumpWidget(
+      new ScrollableViewport2(
+        slivers: <Widget>[
+          new SliverFill(
+            delegate: new SliverChildListDelegate(children),
+          ),
+        ],
+      ),
+    );
+
+    RenderBox box = tester.renderObject<RenderBox>(find.byType(Container).first);
+    expect(box.size.height, equals(600.0));
+
+    expect(find.text('0'), findsOneWidget);
+    expect(find.text('1'), findsNothing);
+    expect(find.text('2'), findsNothing);
+
+    await tester.scroll(find.byType(ScrollableViewport2), const Offset(0.0, -700.0));
+    await tester.pump();
+
+    expect(find.text('0'), findsNothing);
+    expect(find.text('1'), findsOneWidget);
+    expect(find.text('2'), findsOneWidget);
+    expect(find.text('3'), findsNothing);
+    expect(find.text('4'), findsNothing);
+
+    await tester.scroll(find.byType(ScrollableViewport2), const Offset(0.0, 200.0));
+    await tester.pump();
+
+    expect(find.text('0'), findsOneWidget);
+    expect(find.text('1'), findsOneWidget);
+    expect(find.text('2'), findsNothing);
+    expect(find.text('3'), findsNothing);
+  });
+}