Implicit a11y scrolling for iOS (and caching in Viewports) (#17021)

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

@@ -140,11 +140,11 @@ abstract class RenderSliverFixedExtentBoxAdaptor extends RenderSliverMultiBoxAda
 
     final double itemExtent = this.itemExtent;
 
-    final double scrollOffset = constraints.scrollOffset;
+    final double scrollOffset = constraints.scrollOffset + constraints.cacheOrigin;
     assert(scrollOffset >= 0.0);
-    final double remainingPaintExtent = constraints.remainingPaintExtent;
-    assert(remainingPaintExtent >= 0.0);
-    final double targetEndScrollOffset = scrollOffset + remainingPaintExtent;
+    final double remainingExtent = constraints.remainingCacheExtent;
+    assert(remainingExtent >= 0.0);
+    final double targetEndScrollOffset = scrollOffset + remainingExtent;
 
     final BoxConstraints childConstraints = constraints.asBoxConstraints(
       minExtent: itemExtent,
@@ -242,9 +242,16 @@ abstract class RenderSliverFixedExtentBoxAdaptor extends RenderSliverMultiBoxAda
       to: trailingScrollOffset,
     );
 
+    final double cacheExtent = calculateCacheOffset(
+      constraints,
+      from: leadingScrollOffset,
+      to: trailingScrollOffset,
+    );
+
     geometry = new SliverGeometry(
       scrollExtent: estimatedMaxScrollOffset,
       paintExtent: paintExtent,
+      cacheExtent: cacheExtent,
       maxPaintExtent: estimatedMaxScrollOffset,
       // Conservative to avoid flickering away the clip during scroll.
       hasVisualOverflow: (targetLastIndex != null && lastIndex >= targetLastIndex)

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

@@ -513,11 +513,11 @@ class RenderSliverGrid extends RenderSliverMultiBoxAdaptor {
     childManager.didStartLayout();
     childManager.setDidUnderflow(false);
 
-    final double scrollOffset = constraints.scrollOffset;
+    final double scrollOffset = constraints.scrollOffset + constraints.cacheOrigin;
     assert(scrollOffset >= 0.0);
-    final double remainingPaintExtent = constraints.remainingPaintExtent;
-    assert(remainingPaintExtent >= 0.0);
-    final double targetEndScrollOffset = scrollOffset + remainingPaintExtent;
+    final double remainingExtent = constraints.remainingCacheExtent;
+    assert(remainingExtent >= 0.0);
+    final double targetEndScrollOffset = scrollOffset + remainingExtent;
 
     final SliverGridLayout layout = _gridDelegate.getLayout(constraints);
 
@@ -617,11 +617,17 @@ class RenderSliverGrid extends RenderSliverMultiBoxAdaptor {
       from: leadingScrollOffset,
       to: trailingScrollOffset,
     );
+    final double cacheExtent = calculateCacheOffset(
+      constraints,
+      from: leadingScrollOffset,
+      to: trailingScrollOffset,
+    );
 
     geometry = new SliverGeometry(
       scrollExtent: estimatedTotalExtent,
       paintExtent: paintExtent,
       maxPaintExtent: estimatedTotalExtent,
+      cacheExtent: cacheExtent,
       // Conservative to avoid complexity.
       hasVisualOverflow: true,
     );

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

@@ -47,11 +47,11 @@ class RenderSliverList extends RenderSliverMultiBoxAdaptor {
     childManager.didStartLayout();
     childManager.setDidUnderflow(false);
 
-    final double scrollOffset = constraints.scrollOffset;
+    final double scrollOffset = constraints.scrollOffset + constraints.cacheOrigin;
     assert(scrollOffset >= 0.0);
-    final double remainingPaintExtent = constraints.remainingPaintExtent;
-    assert(remainingPaintExtent >= 0.0);
-    final double targetEndScrollOffset = scrollOffset + remainingPaintExtent;
+    final double remainingExtent = constraints.remainingCacheExtent;
+    assert(remainingExtent >= 0.0);
+    final double targetEndScrollOffset = scrollOffset + remainingExtent;
     final BoxConstraints childConstraints = constraints.asBoxConstraints();
     int leadingGarbage = 0;
     int trailingGarbage = 0;
@@ -269,9 +269,15 @@ class RenderSliverList extends RenderSliverMultiBoxAdaptor {
       from: childScrollOffset(firstChild),
       to: endScrollOffset,
     );
+    final double cacheExtent = calculateCacheOffset(
+      constraints,
+      from: childScrollOffset(firstChild),
+      to: endScrollOffset,
+    );
     geometry = new SliverGeometry(
       scrollExtent: estimatedMaxScrollOffset,
       paintExtent: paintExtent,
+      cacheExtent: cacheExtent,
       maxPaintExtent: estimatedMaxScrollOffset,
       // Conservative to avoid flickering away the clip during scroll.
       hasVisualOverflow: endScrollOffset > targetEndScrollOffset || constraints.scrollOffset > 0.0,

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

@@ -298,36 +298,6 @@ abstract class RenderSliverMultiBoxAdaptor extends RenderSliver
     _keepAliveBucket.values.forEach(visitor);
   }
 
-  @override
-  void visitChildrenForSemantics(RenderObjectVisitor visitor) {
-    switch (constraints.normalizedGrowthDirection) {
-      case GrowthDirection.forward:
-        super.visitChildrenForSemantics((RenderObject child) {
-          // The sliver is overlapped at the leading edge; check if trailing edge is visible.
-          final Offset bottomRightInViewport = MatrixUtils.transformPoint(
-              child.getTransformTo(parent), child.semanticBounds.bottomRight
-          );
-          final double endOverlap = constraints.overlap;
-          if ((constraints.axis == Axis.vertical && bottomRightInViewport.dy > endOverlap) ||
-              (constraints.axis == Axis.horizontal && bottomRightInViewport.dx > endOverlap))
-            visitor(child);
-        });
-        break;
-      case GrowthDirection.reverse:
-        super.visitChildrenForSemantics((RenderObject child) {
-          // The sliver is overlapped at the trailing edge; check if leading edge is visible.
-          final Offset topLeftInViewport = MatrixUtils.transformPoint(
-              child.getTransformTo(parent), child.semanticBounds.topLeft
-          );
-          final double startOverlap = constraints.remainingPaintExtent - constraints.overlap;
-          if ((constraints.axis == Axis.vertical && topLeftInViewport.dy < startOverlap) ||
-              (constraints.axis == Axis.horizontal && topLeftInViewport.dx < startOverlap))
-            visitor(child);
-        });
-        break;
-    }
-  }
-
   /// Called during layout to create and add the child with the given index and
   /// scroll offset.
   ///

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

@@ -182,8 +182,10 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
     child.layout(
       constraints.copyWith(
         scrollOffset: math.max(0.0, constraints.scrollOffset - beforePadding),
+        cacheOrigin: math.min(0.0, constraints.cacheOrigin + beforePadding),
         overlap: 0.0,
         remainingPaintExtent: constraints.remainingPaintExtent - calculatePaintOffset(constraints, from: 0.0, to: beforePadding),
+        remainingCacheExtent: constraints.remainingCacheExtent - calculateCacheOffset(constraints, from: 0.0, to: beforePadding),
         crossAxisExtent: math.max(0.0, constraints.crossAxisExtent - crossAxisPadding),
       ),
       parentUsesSize: true,
@@ -206,6 +208,17 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
       to: mainAxisPadding + childLayoutGeometry.scrollExtent,
     );
     final double mainAxisPaddingPaintExtent = beforePaddingPaintExtent + afterPaddingPaintExtent;
+    final double beforePaddingCacheExtent = calculateCacheOffset(
+      constraints,
+      from: 0.0,
+      to: beforePadding,
+    );
+    final double afterPaddingCacheExtent = calculateCacheOffset(
+      constraints,
+      from: beforePadding + childLayoutGeometry.scrollExtent,
+      to: mainAxisPadding + childLayoutGeometry.scrollExtent,
+    );
+    final double mainAxisPaddingCacheExtent = afterPaddingCacheExtent + beforePaddingCacheExtent;
     final double paintExtent = math.min(
       beforePaddingPaintExtent + math.max(childLayoutGeometry.paintExtent, childLayoutGeometry.layoutExtent + afterPaddingPaintExtent),
       constraints.remainingPaintExtent,
@@ -214,6 +227,7 @@ class RenderSliverPadding extends RenderSliver with RenderObjectWithChildMixin<R
       scrollExtent: mainAxisPadding + childLayoutGeometry.scrollExtent,
       paintExtent: paintExtent,
       layoutExtent: math.min(mainAxisPaddingPaintExtent + childLayoutGeometry.layoutExtent, paintExtent),
+      cacheExtent: math.min(mainAxisPaddingCacheExtent + childLayoutGeometry.cacheExtent, constraints.remainingCacheExtent),
       maxPaintExtent: mainAxisPadding + childLayoutGeometry.maxPaintExtent,
       hitTestExtent: math.max(
         mainAxisPaddingPaintExtent + childLayoutGeometry.paintExtent,

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

@@ -292,13 +292,15 @@ abstract class RenderSliverPinnedPersistentHeader extends RenderSliverPersistent
     final bool overlapsContent = constraints.overlap > 0.0;
     excludeFromSemanticsScrolling = overlapsContent || (constraints.scrollOffset > maxExtent - minExtent);
     layoutChild(constraints.scrollOffset, maxExtent, overlapsContent: overlapsContent);
+    final double layoutExtent = (maxExtent - constraints.scrollOffset).clamp(0.0, constraints.remainingPaintExtent);
     geometry = new SliverGeometry(
       scrollExtent: maxExtent,
       paintOrigin: constraints.overlap,
       paintExtent: math.min(childExtent, constraints.remainingPaintExtent),
-      layoutExtent: (maxExtent - constraints.scrollOffset).clamp(0.0, constraints.remainingPaintExtent),
+      layoutExtent: layoutExtent,
       maxPaintExtent: maxExtent,
       maxScrollObstructionExtent: minExtent,
+      cacheExtent: layoutExtent > 0.0 ? -constraints.cacheOrigin + layoutExtent : layoutExtent,
       hasVisualOverflow: true, // Conservatively say we do have overflow to avoid complexity.
     );
   }

packages/flutter/lib/src/semantics/semantics.dart

@@ -794,11 +794,39 @@ class SemanticsNode extends AbstractNode with DiagnosticableTreeMixin {
     }
   }
 
-  /// The clip rect from an ancestor that was applied to this node.
+  /// The semantic clip from an ancestor that was applied to this node.
   ///
   /// Expressed in the coordinate system of the node. May be null if no clip has
   /// been applied.
-  Rect parentClipRect;
+  ///
+  /// Descendant [SemanticsNode]s that are positioned outside of this rect will
+  /// be excluded from the semantics tree. Descendant [SemanticsNode]s that are
+  /// overlapping with this rect, but are outside of [parentPaintClipRect] will
+  /// be included in the tree, but they will be marked as hidden because they
+  /// are assumed to be not visible on screen.
+  ///
+  /// If this rect is null, all descendant [SemanticsNode]s outside of
+  /// [parentPaintClipRect] will be excluded from the tree.
+  ///
+  /// If this rect is non-null it has to completely enclose
+  /// [parentPaintClipRect]. If [parentPaintClipRect] is null this property is
+  /// also null.
+  Rect parentSemanticsClipRect;
+
+  /// The paint clip from an ancestor that was applied to this node.
+  ///
+  /// Expressed in the coordinate system of the node. May be null if no clip has
+  /// been applied.
+  ///
+  /// Descendant [SemanticsNode]s that are positioned outside of this rect will
+  /// either be excluded from the semantics tree (if they have no overlap with
+  /// [parentSemanticsClipRect]) or they will be included and marked as hidden
+  /// (if they are overlapping with [parentSemanticsClipRect]).
+  ///
+  /// This rect is completely enclosed by [parentSemanticsClipRect].
+  ///
+  /// If this rect is null [parentSemanticsClipRect] also has to be null.
+  Rect parentPaintClipRect;
 
   /// Whether the node is invisible.
   ///

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

@@ -564,6 +564,7 @@ class _PageViewState extends State<PageView> {
         physics: physics,
         viewportBuilder: (BuildContext context, ViewportOffset position) {
           return new Viewport(
+            cacheExtent: 0.0,
             axisDirection: axisDirection,
             offset: position,
             slivers: <Widget>[

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

@@ -56,6 +56,7 @@ abstract class ScrollView extends StatelessWidget {
     bool primary,
     ScrollPhysics physics,
     this.shrinkWrap: false,
+    this.cacheExtent,
   }) : assert(reverse != null),
        assert(shrinkWrap != null),
        assert(!(controller != null && primary == true),
@@ -165,6 +166,9 @@ abstract class ScrollView extends StatelessWidget {
   /// Defaults to false.
   final bool shrinkWrap;
 
+  /// {@macro flutter.rendering.viewport.cacheExtent}
+  final double cacheExtent;
+
   /// Returns the [AxisDirection] in which the scroll view scrolls.
   ///
   /// Combines the [scrollDirection] with the [reverse] boolean to obtain the
@@ -211,6 +215,7 @@ abstract class ScrollView extends StatelessWidget {
       axisDirection: axisDirection,
       offset: offset,
       slivers: slivers,
+      cacheExtent: cacheExtent,
     );
   }
 
@@ -333,6 +338,7 @@ class CustomScrollView extends ScrollView {
     bool primary,
     ScrollPhysics physics,
     bool shrinkWrap: false,
+    double cacheExtent,
     this.slivers: const <Widget>[],
   }) : super(
     key: key,
@@ -342,6 +348,7 @@ class CustomScrollView extends ScrollView {
     primary: primary,
     physics: physics,
     shrinkWrap: shrinkWrap,
+    cacheExtent: cacheExtent,
   );
 
   /// The slivers to place inside the viewport.
@@ -372,6 +379,7 @@ abstract class BoxScrollView extends ScrollView {
     ScrollPhysics physics,
     bool shrinkWrap: false,
     this.padding,
+    double cacheExtent,
   }) : super(
     key: key,
     scrollDirection: scrollDirection,
@@ -380,6 +388,7 @@ abstract class BoxScrollView extends ScrollView {
     primary: primary,
     physics: physics,
     shrinkWrap: shrinkWrap,
+    cacheExtent: cacheExtent,
   );
 
   /// The amount of space by which to inset the children.
@@ -594,6 +603,7 @@ class ListView extends BoxScrollView {
     this.itemExtent,
     bool addAutomaticKeepAlives: true,
     bool addRepaintBoundaries: true,
+    double cacheExtent,
     List<Widget> children: const <Widget>[],
   }) : childrenDelegate = new SliverChildListDelegate(
          children,
@@ -608,6 +618,7 @@ class ListView extends BoxScrollView {
     physics: physics,
     shrinkWrap: shrinkWrap,
     padding: padding,
+    cacheExtent: cacheExtent,
   );
 
   /// Creates a scrollable, linear array of widgets that are created on demand.
@@ -648,6 +659,7 @@ class ListView extends BoxScrollView {
     int itemCount,
     bool addAutomaticKeepAlives: true,
     bool addRepaintBoundaries: true,
+    double cacheExtent,
   }) : childrenDelegate = new SliverChildBuilderDelegate(
          itemBuilder,
          childCount: itemCount,
@@ -662,6 +674,7 @@ class ListView extends BoxScrollView {
     physics: physics,
     shrinkWrap: shrinkWrap,
     padding: padding,
+    cacheExtent: cacheExtent
   );
 
   /// Creates a scrollable, linear array of widgets with a custom child model.
@@ -679,6 +692,7 @@ class ListView extends BoxScrollView {
     EdgeInsetsGeometry padding,
     this.itemExtent,
     @required this.childrenDelegate,
+    double cacheExtent,
   }) : assert(childrenDelegate != null),
        super(
          key: key,
@@ -689,6 +703,7 @@ class ListView extends BoxScrollView {
          physics: physics,
          shrinkWrap: shrinkWrap,
          padding: padding,
+        cacheExtent: cacheExtent,
        );
 
   /// If non-null, forces the children to have the given extent in the scroll
@@ -878,6 +893,7 @@ class GridView extends BoxScrollView {
     @required this.gridDelegate,
     bool addAutomaticKeepAlives: true,
     bool addRepaintBoundaries: true,
+    double cacheExtent,
     List<Widget> children: const <Widget>[],
   }) : assert(gridDelegate != null),
        childrenDelegate = new SliverChildListDelegate(
@@ -894,6 +910,7 @@ class GridView extends BoxScrollView {
          physics: physics,
          shrinkWrap: shrinkWrap,
          padding: padding,
+        cacheExtent: cacheExtent,
        );
 
   /// Creates a scrollable, 2D array of widgets that are created on demand.
@@ -929,6 +946,7 @@ class GridView extends BoxScrollView {
     int itemCount,
     bool addAutomaticKeepAlives: true,
     bool addRepaintBoundaries: true,
+    double cacheExtent,
   }) : assert(gridDelegate != null),
        childrenDelegate = new SliverChildBuilderDelegate(
          itemBuilder,
@@ -945,6 +963,7 @@ class GridView extends BoxScrollView {
          physics: physics,
          shrinkWrap: shrinkWrap,
          padding: padding,
+        cacheExtent: cacheExtent,
        );
 
   /// Creates a scrollable, 2D array of widgets with both a custom
@@ -965,6 +984,7 @@ class GridView extends BoxScrollView {
     EdgeInsetsGeometry padding,
     @required this.gridDelegate,
     @required this.childrenDelegate,
+    double cacheExtent,
   }) : assert(gridDelegate != null),
        assert(childrenDelegate != null),
        super(
@@ -976,6 +996,7 @@ class GridView extends BoxScrollView {
          physics: physics,
          shrinkWrap: shrinkWrap,
          padding: padding,
+        cacheExtent: cacheExtent,
        );
 
   /// Creates a scrollable, 2D array of widgets with a fixed number of tiles in
@@ -1007,6 +1028,7 @@ class GridView extends BoxScrollView {
     double childAspectRatio: 1.0,
     bool addAutomaticKeepAlives: true,
     bool addRepaintBoundaries: true,
+    double cacheExtent,
     List<Widget> children: const <Widget>[],
   }) : gridDelegate = new SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: crossAxisCount,
@@ -1027,6 +1049,7 @@ class GridView extends BoxScrollView {
     physics: physics,
     shrinkWrap: shrinkWrap,
     padding: padding,
+    cacheExtent: cacheExtent,
   );
 
   /// Creates a scrollable, 2D array of widgets with tiles that each have a

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

@@ -323,11 +323,14 @@ class _RenderSingleChildViewport extends RenderBox with RenderObjectWithChildMix
   _RenderSingleChildViewport({
     AxisDirection axisDirection: AxisDirection.down,
     @required ViewportOffset offset,
+    double cacheExtent: RenderAbstractViewport.defaultCacheExtent,
     RenderBox child,
   }) : assert(axisDirection != null),
        assert(offset != null),
+       assert(cacheExtent != null),
        _axisDirection = axisDirection,
-       _offset = offset {
+       _offset = offset,
+       _cacheExtent = cacheExtent {
     this.child = child;
   }
 
@@ -357,6 +360,17 @@ class _RenderSingleChildViewport extends RenderBox with RenderObjectWithChildMix
     markNeedsLayout();
   }
 
+  /// {@macro flutter.rendering.viewport.cacheExtent}
+  double get cacheExtent => _cacheExtent;
+  double _cacheExtent;
+  set cacheExtent(double value) {
+    assert(value != null);
+    if (value == _cacheExtent)
+      return;
+    _cacheExtent = value;
+    markNeedsLayout();
+  }
+
   void _hasScrolled() {
     markNeedsPaint();
     markNeedsSemanticsUpdate();
@@ -588,4 +602,26 @@ class _RenderSingleChildViewport extends RenderBox with RenderObjectWithChildMix
     // Make sure the viewport itself is on screen.
     super.showOnScreen();
   }
+
+  @override
+  Rect describeSemanticsClip(RenderObject child) {
+    assert(axis != null);
+    switch (axis) {
+      case Axis.vertical:
+        return new Rect.fromLTRB(
+          semanticBounds.left,
+          semanticBounds.top - cacheExtent,
+          semanticBounds.right,
+          semanticBounds.bottom + cacheExtent,
+        );
+      case Axis.horizontal:
+        return new Rect.fromLTRB(
+          semanticBounds.left - cacheExtent,
+          semanticBounds.top,
+          semanticBounds.right + cacheExtent,
+          semanticBounds.bottom,
+        );
+    }
+    return null;
+  }
 }

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

@@ -888,6 +888,25 @@ class SliverMultiBoxAdaptorElement extends RenderObjectElement implements Render
    assert(!_childElements.values.any((Element child) => child == null));
     _childElements.values.toList().forEach(visitor);
   }
+
+  @override
+  void debugVisitOnstageChildren(ElementVisitor visitor) {
+    _childElements.values.where((Element child) {
+      final SliverMultiBoxAdaptorParentData parentData = child.renderObject.parentData;
+      double itemExtent;
+      switch (renderObject.constraints.axis) {
+        case Axis.horizontal:
+          itemExtent = child.renderObject.paintBounds.width;
+          break;
+        case Axis.vertical:
+          itemExtent = child.renderObject.paintBounds.height;
+          break;
+      }
+
+      return parentData.layoutOffset < renderObject.constraints.scrollOffset + renderObject.constraints.remainingPaintExtent &&
+          parentData.layoutOffset + itemExtent > renderObject.constraints.scrollOffset;
+    }).forEach(visitor);
+  }
 }
 
 /// A sliver that contains a single box child that fills the remaining space in

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

@@ -56,6 +56,7 @@ class Viewport extends MultiChildRenderObjectWidget {
     this.anchor: 0.0,
     @required this.offset,
     this.center,
+    this.cacheExtent,
     List<Widget> slivers: const <Widget>[],
   }) : assert(offset != null),
        assert(slivers != null),
@@ -108,6 +109,9 @@ class Viewport extends MultiChildRenderObjectWidget {
   /// The [center] must be the key of a child of the viewport.
   final Key center;
 
+  /// {@macro flutter.rendering.viewport.cacheExtent}
+  final double cacheExtent;
+
   /// Given a [BuildContext] and an [AxisDirection], determine the correct cross
   /// axis direction.
   ///
@@ -135,6 +139,7 @@ class Viewport extends MultiChildRenderObjectWidget {
       crossAxisDirection: crossAxisDirection ?? Viewport.getDefaultCrossAxisDirection(context, axisDirection),
       anchor: anchor,
       offset: offset,
+      cacheExtent: cacheExtent,
     );
   }
 
@@ -144,7 +149,8 @@ class Viewport extends MultiChildRenderObjectWidget {
       ..axisDirection = axisDirection
       ..crossAxisDirection = crossAxisDirection ?? Viewport.getDefaultCrossAxisDirection(context, axisDirection)
       ..anchor = anchor
-      ..offset = offset;
+      ..offset = offset
+      ..cacheExtent = cacheExtent;
   }
 
   @override
@@ -199,6 +205,14 @@ class _ViewportElement extends MultiChildRenderObjectElement {
       renderObject.center = null;
     }
   }
+
+  @override
+  void debugVisitOnstageChildren(ElementVisitor visitor) {
+    children.where((Element e) {
+      final RenderSliver renderSliver = e.renderObject;
+      return renderSliver.geometry.visible;
+    }).forEach(visitor);
+  }
 }
 
 /// A widget that is bigger on the inside and shrink wraps its children in the

packages/flutter/test/cupertino/refresh_test.dart

@@ -430,11 +430,11 @@ void main() {
 
       // Now the sliver is scrolled off screen.
       expect(
-        tester.getTopLeft(find.widgetWithText(Center, '-1')).dy,
+        tester.getTopLeft(find.widgetWithText(Center, '-1', skipOffstage: false)).dy,
         moreOrLessEquals(-175.38461538461536),
       );
       expect(
-        tester.getBottomLeft(find.widgetWithText(Center, '-1')).dy,
+        tester.getBottomLeft(find.widgetWithText(Center, '-1', skipOffstage: false)).dy,
         moreOrLessEquals(-115.38461538461536),
       );
       expect(
@@ -720,11 +720,11 @@ void main() {
 
         // Now the sliver is scrolled off screen.
         expect(
-          tester.getTopLeft(find.widgetWithText(Center, '-1')).dy,
+          tester.getTopLeft(find.widgetWithText(Center, '-1', skipOffstage: false)).dy,
           moreOrLessEquals(-175.38461538461536),
         );
         expect(
-          tester.getBottomLeft(find.widgetWithText(Center, '-1')).dy,
+          tester.getBottomLeft(find.widgetWithText(Center, '-1', skipOffstage: false)).dy,
           moreOrLessEquals(-115.38461538461536),
         );
 
@@ -872,7 +872,7 @@ void main() {
       );
 
       expect(
-        CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder))),
+        CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder, skipOffstage: false))),
         RefreshIndicatorMode.inactive,
       );
 
@@ -907,7 +907,7 @@ void main() {
       await tester.pump(const Duration(seconds: 2));
 
       expect(
-        CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder))),
+        CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder, skipOffstage: false))),
         RefreshIndicatorMode.inactive,
       );
 
@@ -1147,7 +1147,7 @@ void main() {
           moreOrLessEquals(-145.0332383665717),
         );
         expect(
-          CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder))),
+          CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder, skipOffstage: false))),
           RefreshIndicatorMode.refresh,
         );
 
@@ -1155,7 +1155,7 @@ void main() {
         // The sliver layout extent is removed on next frame.
         await tester.pump();
         expect(
-          CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder))),
+          CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder, skipOffstage: false))),
           RefreshIndicatorMode.inactive,
         );
         // Nothing moved.
@@ -1208,7 +1208,7 @@ void main() {
         await tester.pump(const Duration(seconds: 5));
         // In refresh mode but has no UI.
         expect(
-          CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder))),
+          CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder, skipOffstage: false))),
           RefreshIndicatorMode.refresh,
         );
         expect(
@@ -1221,7 +1221,7 @@ void main() {
         await tester.pump();
         // Goes to inactive right away since the sliver is already collapsed.
         expect(
-          CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder))),
+          CupertinoRefreshControl.state(tester.element(find.byType(LayoutBuilder, skipOffstage: false))),
           RefreshIndicatorMode.inactive,
         );
 

packages/flutter/test/material/app_bar_test.dart

@@ -54,16 +54,11 @@ ScrollController primaryScrollController(WidgetTester tester) {
   return PrimaryScrollController.of(tester.element(find.byType(CustomScrollView)));
 }
 
-bool appBarIsVisible(WidgetTester tester) {
-  final RenderSliver sliver = tester.element(find.byType(SliverAppBar)).findRenderObject();
-  return sliver.geometry.visible;
-}
-
-double appBarHeight(WidgetTester tester) => tester.getSize(find.byType(AppBar)).height;
-double appBarTop(WidgetTester tester) => tester.getTopLeft(find.byType(AppBar)).dy;
-double appBarBottom(WidgetTester tester) => tester.getBottomLeft(find.byType(AppBar)).dy;
+double appBarHeight(WidgetTester tester) => tester.getSize(find.byType(AppBar, skipOffstage: false)).height;
+double appBarTop(WidgetTester tester) => tester.getTopLeft(find.byType(AppBar, skipOffstage: false)).dy;
+double appBarBottom(WidgetTester tester) => tester.getBottomLeft(find.byType(AppBar, skipOffstage: false)).dy;
 
-double tabBarHeight(WidgetTester tester) => tester.getSize(find.byType(TabBar)).height;
+double tabBarHeight(WidgetTester tester) => tester.getSize(find.byType(TabBar, skipOffstage: false)).height;
 
 void main() {
   setUp(() {
@@ -592,7 +587,7 @@ void main() {
 
     final ScrollController controller = primaryScrollController(tester);
     expect(controller.offset, 0.0);
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
 
     final double initialAppBarHeight = appBarHeight(tester);
     final double initialTabBarHeight = tabBarHeight(tester);
@@ -600,21 +595,21 @@ void main() {
     // Scroll the not-pinned appbar partially out of view
     controller.jumpTo(50.0);
     await tester.pump();
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
     expect(appBarHeight(tester), initialAppBarHeight);
     expect(tabBarHeight(tester), initialTabBarHeight);
 
     // Scroll the not-pinned appbar out of view
     controller.jumpTo(600.0);
     await tester.pump();
-    expect(appBarIsVisible(tester), false);
+    expect(find.byType(SliverAppBar), findsNothing);
     expect(appBarHeight(tester), initialAppBarHeight);
     expect(tabBarHeight(tester), initialTabBarHeight);
 
     // Scroll the not-pinned appbar back into view
     controller.jumpTo(0.0);
     await tester.pump();
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
     expect(appBarHeight(tester), initialAppBarHeight);
     expect(tabBarHeight(tester), initialTabBarHeight);
   });
@@ -629,7 +624,7 @@ void main() {
 
     final ScrollController controller = primaryScrollController(tester);
     expect(controller.offset, 0.0);
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
     expect(appBarHeight(tester), 128.0);
 
     const double initialAppBarHeight = 128.0;
@@ -639,7 +634,7 @@ void main() {
     // point both the toolbar and the tabbar are visible.
     controller.jumpTo(600.0);
     await tester.pump();
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
     expect(tabBarHeight(tester), initialTabBarHeight);
     expect(appBarHeight(tester), lessThan(initialAppBarHeight));
     expect(appBarHeight(tester), greaterThan(initialTabBarHeight));
@@ -647,7 +642,7 @@ void main() {
     // Scroll the not-pinned appbar back into view
     controller.jumpTo(0.0);
     await tester.pump();
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
     expect(appBarHeight(tester), initialAppBarHeight);
     expect(tabBarHeight(tester), initialTabBarHeight);
   });
@@ -662,7 +657,7 @@ void main() {
 
     final ScrollController controller = primaryScrollController(tester);
     expect(controller.offset, 0.0);
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
     expect(appBarHeight(tester), 128.0);
 
     const double initialAppBarHeight = 128.0;
@@ -672,7 +667,7 @@ void main() {
     // point only the tabBar is visible.
     controller.jumpTo(600.0);
     await tester.pump();
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
     expect(tabBarHeight(tester), initialTabBarHeight);
     expect(appBarHeight(tester), lessThan(initialAppBarHeight));
     expect(appBarHeight(tester), initialTabBarHeight);
@@ -680,7 +675,7 @@ void main() {
     // Scroll the floating-pinned appbar back into view
     controller.jumpTo(0.0);
     await tester.pump();
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
     expect(appBarHeight(tester), initialAppBarHeight);
     expect(tabBarHeight(tester), initialTabBarHeight);
   });
@@ -692,7 +687,7 @@ void main() {
       snap: true,
       expandedHeight: 128.0,
     ));
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
     expect(appBarTop(tester), 0.0);
     expect(appBarHeight(tester), 128.0);
     expect(appBarBottom(tester), 128.0);
@@ -701,7 +696,7 @@ void main() {
     final ScrollPosition position = tester.state<ScrollableState>(find.byType(Scrollable)).position;
     position.jumpTo(256.00);
     await tester.pumpAndSettle();
-    expect(appBarIsVisible(tester), false);
+    expect(find.byType(SliverAppBar), findsNothing);
     expect(appBarTop(tester), lessThanOrEqualTo(-128.0));
 
     // Drag the scrollable up and down. The app bar should not snap open, its
@@ -773,7 +768,7 @@ void main() {
       snap: true,
       expandedHeight: 128.0,
     ));
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
     expect(appBarTop(tester), 0.0);
     expect(appBarHeight(tester), 128.0);
     expect(appBarBottom(tester), 128.0);
@@ -783,7 +778,7 @@ void main() {
     final ScrollPosition position = tester.state<ScrollableState>(find.byType(Scrollable)).position;
     position.jumpTo(256.0);
     await tester.pumpAndSettle();
-    expect(appBarIsVisible(tester), true);
+    expect(find.byType(SliverAppBar), findsOneWidget);
     expect(appBarTop(tester), 0.0);
     expect(appBarHeight(tester), kTextTabBarHeight);
 

packages/flutter/test/material/tabs_test.dart

@@ -289,7 +289,7 @@ void main() {
     }
 
     StateMarkerState findStateMarkerState(String name) {
-      return tester.state(find.widgetWithText(StateMarker, name));
+      return tester.state(find.widgetWithText(StateMarker, name, skipOffstage: false));
     }
 
     await tester.pumpWidget(builder());

packages/flutter/test/material/text_field_focus_test.dart

@@ -162,7 +162,7 @@ void main() {
 
     await tester.drag(find.byType(ListView), const Offset(0.0, -1000.0));
     await tester.pump();
-    expect(find.byType(TextField), findsOneWidget);
+    expect(find.byType(TextField, skipOffstage: false), findsOneWidget);
     expect(tester.testTextInput.isVisible, isTrue);
 
     focusNode.unfocus();
@@ -201,10 +201,10 @@ void main() {
     expect(find.byType(TextField), findsOneWidget);
     await tester.drag(find.byType(ListView), const Offset(0.0, -1000.0));
     await tester.pump();
-    expect(find.byType(TextField), findsOneWidget);
+    expect(find.byType(TextField, skipOffstage: false), findsOneWidget);
     await tester.pumpWidget(makeTest('test'));
     await tester.pump(); // in case the AutomaticKeepAlive widget thinks it needs a cleanup frame
-    expect(find.byType(TextField), findsOneWidget);
+    expect(find.byType(TextField, skipOffstage: false), findsOneWidget);
   });
 
   testWidgets('TextField with decoration:null', (WidgetTester tester) async {

packages/flutter/test/rendering/slivers_block_test.dart

@@ -83,6 +83,7 @@ void main() {
       axisDirection: AxisDirection.down,
       crossAxisDirection: AxisDirection.right,
       offset: new ViewportOffset.zero(),
+      cacheExtent: 0.0,
       children: <RenderSliver>[
         inner = childManager.createRenderObject(),
       ],
@@ -161,6 +162,7 @@ void main() {
       children: <RenderSliver>[
         inner = childManager.createRenderObject(),
       ],
+      cacheExtent: 0.0,
     );
     layout(root);
 

packages/flutter/test/rendering/slivers_helpers_test.dart

@@ -27,6 +27,8 @@ void main() {
       crossAxisExtent: 0.0,
       crossAxisDirection: AxisDirection.right,
       viewportMainAxisExtent: 0.0,
+      cacheOrigin: 0.0,
+      remainingCacheExtent: 0.0,
     );
     final SliverConstraints b = a.copyWith();
     expect(a, equals(b));
@@ -55,6 +57,8 @@ void main() {
       crossAxisExtent: 40.0,
       crossAxisDirection: AxisDirection.right,
       viewportMainAxisExtent: 30.0,
+      cacheOrigin: 0.0,
+      remainingCacheExtent: 0.0,
     );
     expect(c, equals(d));
     expect(c.normalizedGrowthDirection, equals(GrowthDirection.forward));

packages/flutter/test/widgets/animated_list_test.dart

@@ -60,9 +60,9 @@ void main() {
       ),
     );
 
-    double itemHeight(int index) => tester.getSize(find.byKey(new ValueKey<int>(index))).height;
-    double itemTop(int index) => tester.getTopLeft(find.byKey(new ValueKey<int>(index))).dy;
-    double itemBottom(int index) => tester.getBottomLeft(find.byKey(new ValueKey<int>(index))).dy;
+    double itemHeight(int index) => tester.getSize(find.byKey(new ValueKey<int>(index), skipOffstage: false)).height;
+    double itemTop(int index) => tester.getTopLeft(find.byKey(new ValueKey<int>(index), skipOffstage: false)).dy;
+    double itemBottom(int index) => tester.getBottomLeft(find.byKey(new ValueKey<int>(index), skipOffstage: false)).dy;
 
     listKey.currentState.insertItem(0, duration: const Duration(milliseconds: 100));
     await tester.pump();

packages/flutter/test/widgets/grid_view_test.dart

@@ -168,9 +168,17 @@ void main() {
       0, 1, 2, // col 0
       3, 4, 5, // col 1
       6, 7, 8, // col 2
+      9, 10, 11, // col 3 (in cached area)
     ]));
     log.clear();
 
+    for (int i = 0; i < 9; i++) {
+      expect(find.text('$i'), findsOneWidget);
+    }
+    for (int i = 9; i < 80; i++) {
+      expect(find.text('$i'), findsNothing);
+    }
+
     final ScrollableState state = tester.state(find.byType(Scrollable));
     final ScrollPosition position = state.position;
     position.jumpTo(3025.0);
@@ -179,25 +187,49 @@ void main() {
     await tester.pump();
 
     expect(log, equals(<int>[
+      30, 31, 32, // col 10 (in cached area)
       33, 34, 35, // col 11
       36, 37, 38, // col 12
       39, 40, 41, // col 13
       42, 43, 44, // col 14
+      45, 46, 47, // col 15 (in cached area)
     ]));
     log.clear();
 
+    for (int i = 0; i < 33; i++) {
+      expect(find.text('$i'), findsNothing);
+    }
+    for (int i = 33; i < 45; i++) {
+      expect(find.text('$i'), findsOneWidget);
+    }
+    for (int i = 45; i < 80; i++) {
+      expect(find.text('$i'), findsNothing);
+    }
+
     position.jumpTo(975.0);
 
     expect(log, isEmpty);
     await tester.pump();
 
     expect(log, equals(<int>[
+      6, 7, 8, // col2 (in cached area)
       9, 10, 11, // col 3
       12, 13, 14, // col 4
       15, 16, 17, // col 5
       18, 19, 20, // col 6
+      21, 22, 23, // col 7 (in cached area)
     ]));
     log.clear();
+
+    for (int i = 0; i < 9; i++) {
+      expect(find.text('$i'), findsNothing);
+    }
+    for (int i = 9; i < 21; i++) {
+      expect(find.text('$i'), findsOneWidget);
+    }
+    for (int i = 21; i < 80; i++) {
+      expect(find.text('$i'), findsNothing);
+    }
   });
 
   testWidgets('GridView - change crossAxisCount', (WidgetTester tester) async {
@@ -230,7 +262,15 @@ void main() {
       0, 1, 2, 3, // row 0
       4, 5, 6, 7, // row 1
       8, 9, 10, 11, // row 2
+      12, 13, 14, 15, // row 3 (in cached area)
+      16, 17, 18, 19, // row 4 (in cached area)
     ]));
+    for (int i = 0; i < 12; i++) {
+      expect(find.text('$i'), findsOneWidget);
+    }
+    for (int i = 12; i < 40; i++) {
+      expect(find.text('$i'), findsNothing);
+    }
     log.clear();
 
     await tester.pumpWidget(
@@ -258,6 +298,8 @@ void main() {
       0, 1, 2, 3, // row 0
       4, 5, 6, 7, // row 1
       8, 9, 10, 11, // row 2
+      12, 13, 14, 15, // row 3 (in cached area)
+      16, 17, 18, 19, // row 4 (in cached area)
     ]));
     log.clear();
 
@@ -295,7 +337,15 @@ void main() {
       0, 1, 2, 3, // row 0
       4, 5, 6, 7, // row 1
       8, 9, 10, 11, // row 2
+      12, 13, 14, 15, // row 3 (in cached area)
+      16, 17, 18, 19, // row 4 (in cached area)
     ]));
+    for (int i = 0; i < 12; i++) {
+      expect(find.text('$i'), findsOneWidget);
+    }
+    for (int i = 12; i < 40; i++) {
+      expect(find.text('$i'), findsNothing);
+    }
     log.clear();
 
     await tester.pumpWidget(
@@ -323,6 +373,8 @@ void main() {
       0, 1, 2, 3, // row 0
       4, 5, 6, 7, // row 1
       8, 9, 10, 11, // row 2
+      12, 13, 14, 15, // row 3 (in cached area)
+      16, 17, 18, 19, // row 4 (in cached area)
     ]));
     log.clear();
 
@@ -346,6 +398,7 @@ void main() {
           child: new SizedBox(
             height: 200.0,
             child: new GridView.count(
+              cacheExtent: 0.0,
               crossAxisCount: 2,
               children: <Widget>[ container, container, container, container ],
             ),
@@ -379,7 +432,7 @@ void main() {
       ),
     );
 
-    expect(find.text('0'), findsOneWidget);
+    expect(find.text('0'), findsNothing);
     expect(find.text('1'), findsNothing);
   });
 

packages/flutter/test/widgets/heroes_test.dart

@@ -781,6 +781,7 @@ void main() {
       builder: (BuildContext context) {
         return new Material(
           child: new ListView(
+            cacheExtent: 0.0,
             children: <Widget>[
               const SizedBox(height: 100.0),
               // This container will appear at Y=100

packages/flutter/test/widgets/list_view_builder_test.dart

@@ -38,7 +38,11 @@ void main() {
 
     final FlipWidgetState testWidget = tester.state(find.byType(FlipWidget));
 
-    expect(callbackTracker, equals(<int>[0, 1, 2, 3, 4, 5]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, 2, 3, 4, 5, // visible in viewport
+      6, 7, 8, // in caching area
+    ]));
+    check(visible: <int>[0, 1, 2, 3, 4, 5], hidden: <int>[ 6, 7, 8]);
 
     callbackTracker.clear();
     testWidget.flip();
@@ -50,7 +54,11 @@ void main() {
     testWidget.flip();
     await tester.pump();
 
-    expect(callbackTracker, equals(<int>[0, 1, 2, 3, 4, 5]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, 2, 3, 4, 5,
+      6, 7, 8, // in caching area
+    ]));
+    check(visible: <int>[0, 1, 2, 3, 4, 5], hidden: <int>[ 6, 7, 8]);
   });
 
   testWidgets('ListView.builder vertical', (WidgetTester tester) async {
@@ -91,7 +99,12 @@ void main() {
 
     await tester.pumpWidget(buildWidget());
 
-    expect(callbackTracker, equals(<int>[1, 2, 3, 4]));
+    expect(callbackTracker, equals(<int>[
+      0, // in caching area
+      1, 2, 3, 4,
+      5, // in caching area
+    ]));
+    check(visible: <int>[1, 2, 3, 4], hidden: <int>[0, 5]);
     callbackTracker.clear();
 
     jumpTo(400.0);
@@ -99,12 +112,12 @@ void main() {
 
     await tester.pumpWidget(buildWidget());
 
-    expect(callbackTracker, equals(<int>[1, 2, 3, 4]));
-    callbackTracker.clear();
-
-    await tester.pumpWidget(buildWidget());
-
-    expect(callbackTracker, equals(<int>[2, 3, 4]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, // in caching area
+      2, 3, 4,
+      5, 6, // in caching area
+    ]));
+    check(visible: <int>[2, 3, 4], hidden: <int>[0, 1, 5, 6]);
     callbackTracker.clear();
 
     jumpTo(500.0);
@@ -112,7 +125,12 @@ void main() {
 
     await tester.pumpWidget(buildWidget());
 
-    expect(callbackTracker, equals(<int>[2, 3, 4, 5]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, // in caching area
+      2, 3, 4, 5,
+      6, // in caching area
+    ]));
+    check(visible: <int>[2, 3, 4, 5], hidden: <int>[0, 1, 6]);
     callbackTracker.clear();
   });
 
@@ -155,8 +173,12 @@ void main() {
 
     await tester.pumpWidget(buildWidget());
 
-    expect(callbackTracker, equals(<int>[1, 2, 3, 4, 5]));
-
+    expect(callbackTracker, equals(<int>[
+      0, // in caching area
+      1, 2, 3, 4, 5,
+      6, // in caching area
+    ]));
+    check(visible: <int>[1, 2, 3, 4, 5], hidden: <int>[0, 6]);
     callbackTracker.clear();
 
     jumpTo(400.0);
@@ -164,12 +186,12 @@ void main() {
 
     await tester.pumpWidget(buildWidget());
 
-    expect(callbackTracker, equals(<int>[1, 2, 3, 4, 5]));
-    callbackTracker.clear();
-
-    await tester.pumpWidget(buildWidget());
-
-    expect(callbackTracker, equals(<int>[2, 3, 4, 5]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, // in caching area
+      2, 3, 4, 5,
+      6, 7, // in caching area
+    ]));
+    check(visible: <int>[2, 3, 4, 5], hidden: <int>[0, 1, 6, 7]);
     callbackTracker.clear();
 
     jumpTo(500.0);
@@ -177,7 +199,12 @@ void main() {
 
     await tester.pumpWidget(buildWidget());
 
-    expect(callbackTracker, equals(<int>[2, 3, 4, 5, 6]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, // in caching area
+      2, 3, 4, 5, 6,
+      7, // in caching area
+    ]));
+    check(visible: <int>[2, 3, 4, 5, 6], hidden: <int>[0, 1, 7]);
     callbackTracker.clear();
   });
 
@@ -208,26 +235,39 @@ void main() {
     }
 
     await tester.pumpWidget(testWidget);
-    expect(callbackTracker, equals(<int>[0, 1]));
+    expect(callbackTracker, equals(<int>[0, 1, 2]));
+    check(visible: <int>[0, 1], hidden: <int>[2]);
     callbackTracker.clear();
 
     jumpTo(150.0);
     await tester.pump();
 
-    expect(callbackTracker, equals(<int>[2]));
+    expect(callbackTracker, equals(<int>[3]));
+    check(visible: <int>[0, 1, 2], hidden: <int>[3]);
     callbackTracker.clear();
 
     jumpTo(600.0);
     await tester.pump();
 
-    expect(callbackTracker, equals(<int>[3]));
+    expect(callbackTracker, equals(<int>[4]));
+    check(visible: <int>[2, 3], hidden: <int>[0, 1, 4]);
     callbackTracker.clear();
 
     jumpTo(750.0);
     await tester.pump();
 
-    expect(callbackTracker, equals(<int>[4]));
+    expect(callbackTracker, equals(<int>[5]));
+    check(visible: <int>[2, 3, 4], hidden: <int>[0, 1, 5]);
     callbackTracker.clear();
   });
 
 }
+
+void check({List<int> visible: const <int>[], List<int> hidden: const <int>[]}) {
+  for (int i in visible) {
+    expect(find.text('$i'), findsOneWidget);
+  }
+  for (int i in hidden) {
+    expect(find.text('$i'), findsNothing);
+  }
+}

packages/flutter/test/widgets/list_view_correction_test.dart

@@ -12,6 +12,7 @@ void main() {
       new Directionality(
         textDirection: TextDirection.ltr,
         child: new ListView(
+          cacheExtent: 0.0,
           controller: controller,
           children: <Widget>[
             new Container(height: 400.0, child: const Text('1')),
@@ -34,6 +35,7 @@ void main() {
       new Directionality(
         textDirection: TextDirection.ltr,
         child: new ListView(
+          cacheExtent: 0.0,
           controller: controller,
           children: <Widget>[
             new Container(height: 200.0, child: const Text('1')),
@@ -53,16 +55,73 @@ void main() {
     controller.jumpTo(300.0);
     await tester.pump();
 
+    expect(controller.offset, equals(300.0));
     expect(tester.getTopLeft(find.text('2')).dy, equals(100.0));
 
     controller.jumpTo(50.0);
-
     await tester.pump();
 
     expect(controller.offset, equals(0.0));
     expect(tester.getTopLeft(find.text('2')).dy, equals(200.0));
   });
 
+  testWidgets('ListView can handle shrinking top elements with cache extent', (WidgetTester tester) async {
+    final ScrollController controller = new ScrollController();
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new ListView(
+          controller: controller,
+          children: <Widget>[
+            new Container(height: 400.0, child: const Text('1')),
+            new Container(height: 400.0, child: const Text('2')),
+            new Container(height: 400.0, child: const Text('3')),
+            new Container(height: 400.0, child: const Text('4')),
+            new Container(height: 400.0, child: const Text('5')),
+            new Container(height: 400.0, child: const Text('6')),
+          ],
+        ),
+      ),
+    );
+
+    controller.jumpTo(1000.0);
+    await tester.pump();
+
+    expect(tester.getTopLeft(find.text('4')).dy, equals(200.0));
+
+    await tester.pumpWidget(
+      new Directionality(
+        textDirection: TextDirection.ltr,
+        child: new ListView(
+          controller: controller,
+          children: <Widget>[
+            new Container(height: 200.0, child: const Text('1')),
+            new Container(height: 400.0, child: const Text('2')),
+            new Container(height: 400.0, child: const Text('3')),
+            new Container(height: 400.0, child: const Text('4')),
+            new Container(height: 400.0, child: const Text('5')),
+            new Container(height: 400.0, child: const Text('6')),
+          ],
+        ),
+      ),
+    );
+
+    expect(controller.offset, equals(1000.0));
+    expect(tester.getTopLeft(find.text('4')).dy, equals(200.0));
+
+    controller.jumpTo(300.0);
+    await tester.pump();
+
+    expect(controller.offset, equals(250.0));
+    expect(tester.getTopLeft(find.text('2')).dy, equals(-50.0));
+
+    controller.jumpTo(50.0);
+    await tester.pump();
+
+    expect(controller.offset, equals(50.0));
+    expect(tester.getTopLeft(find.text('2')).dy, equals(150.0));
+  });
+
   testWidgets('ListView can handle inserts at 0', (WidgetTester tester) async {
     final ScrollController controller = new ScrollController();
     await tester.pumpWidget(

packages/flutter/test/widgets/list_view_misc_test.dart

@@ -150,7 +150,7 @@ void main() {
       ),
     );
 
-    final SliverMultiBoxAdaptorElement element = tester.element(find.byType(SliverList));
+    final SliverMultiBoxAdaptorElement element = tester.element(find.byType(SliverList, skipOffstage: false));
 
     final double maxScrollOffset = element.estimateMaxScrollOffset(
       null,

packages/flutter/test/widgets/list_view_test.dart

@@ -96,7 +96,7 @@ void main() {
       ),
     );
 
-    expect(log, equals(<int>[0, 1, 2]));
+    expect(log, equals(<int>[0, 1, 2, 3, 4]));
     log.clear();
 
     final ScrollableState state = tester.state(find.byType(Scrollable));
@@ -106,7 +106,7 @@ void main() {
     expect(log, isEmpty);
     await tester.pump();
 
-    expect(log, equals(<int>[10, 11, 12, 13]));
+    expect(log, equals(<int>[8, 9, 10, 11, 12, 13, 14]));
     log.clear();
 
     position.jumpTo(975.0);
@@ -114,7 +114,7 @@ void main() {
     expect(log, isEmpty);
     await tester.pump();
 
-    expect(log, equals(<int>[4, 5, 6, 7]));
+    expect(log, equals(<int>[7, 6, 5, 4, 3]));
     log.clear();
   });
 
@@ -196,7 +196,7 @@ void main() {
         ),
       ),
     );
-    expect(find.text('padded'), findsOneWidget);
+    expect(find.text('padded', skipOffstage: false), findsOneWidget);
   });
 
   testWidgets('ListView with itemExtent in unbounded context', (WidgetTester tester) async {
@@ -240,7 +240,7 @@ void main() {
       ),
     );
 
-    expect(delegate.log, equals(<String>['didFinishLayout firstIndex=0 lastIndex=5']));
+    expect(delegate.log, equals(<String>['didFinishLayout firstIndex=0 lastIndex=7']));
     delegate.log.clear();
 
     await tester.pumpWidget(
@@ -253,7 +253,7 @@ void main() {
       ),
     );
 
-    expect(delegate.log, equals(<String>['didFinishLayout firstIndex=0 lastIndex=2']));
+    expect(delegate.log, equals(<String>['didFinishLayout firstIndex=0 lastIndex=4']));
     delegate.log.clear();
 
     await tester.drag(find.byType(ListView), const Offset(0.0, -600.0));
@@ -262,7 +262,7 @@ void main() {
 
     await tester.pump();
 
-    expect(delegate.log, equals(<String>['didFinishLayout firstIndex=2 lastIndex=5']));
+    expect(delegate.log, equals(<String>['didFinishLayout firstIndex=1 lastIndex=6']));
     delegate.log.clear();
   });
 

packages/flutter/test/widgets/list_view_viewporting_test.dart

@@ -38,7 +38,10 @@ void main() {
 
     final FlipWidgetState testWidget = tester.state(find.byType(FlipWidget));
 
-    expect(callbackTracker, equals(<int>[0, 1, 2, 3, 4, 5]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, 2, 3, 4, 5, // visible
+      6, 7, 8 // in cached area
+    ]));
 
     callbackTracker.clear();
     testWidget.flip();
@@ -50,7 +53,10 @@ void main() {
     testWidget.flip();
     await tester.pump();
 
-    expect(callbackTracker, equals(<int>[0, 1, 2, 3, 4, 5]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, 2, 3, 4, 5, // visible
+      6, 7, 8, // in cached area
+    ]));
   });
 
   testWidgets('ListView vertical', (WidgetTester tester) async {
@@ -86,22 +92,34 @@ void main() {
     await tester.pumpWidget(builder());
 
     // 0 is built to find its height
-    expect(callbackTracker, equals(<int>[0, 1, 2, 3, 4]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, 2, 3, 4,
+      5, // in cached area
+    ]));
     callbackTracker.clear();
 
     final ScrollableState scrollable = tester.state(find.byType(Scrollable));
-    scrollable.position.jumpTo(400.0); // now only 3 should fit, numbered 2-4.
+    scrollable.position.jumpTo(600.0); // now only 3 should fit, numbered 3-5.
 
     await tester.pumpWidget(builder());
 
     // We build the visible children to find their new size.
-    expect(callbackTracker, equals(<int>[1, 2, 3, 4]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, 2,
+      3, 4, 5, //visible
+      6, 7
+    ]));
     callbackTracker.clear();
 
     await tester.pumpWidget(builder());
 
     // 0 isn't built because they're not visible.
-    expect(callbackTracker, equals(<int>[1, 2, 3, 4]));
+    expect(callbackTracker, equals(<int>[
+      1, 2,
+      3, 4, 5, // visible
+      6, 7,
+    ]
+    ));
     callbackTracker.clear();
   });
 
@@ -128,7 +146,7 @@ void main() {
         child: new FlipWidget(
           left: new ListView.builder(
             scrollDirection: Axis.horizontal,
-            controller: new ScrollController(initialScrollOffset: 300.0),
+            controller: new ScrollController(initialScrollOffset: 500.0),
             itemBuilder: itemBuilder,
           ),
           right: const Text('Not Today'),
@@ -139,23 +157,23 @@ void main() {
     await tester.pumpWidget(builder());
 
     // 0 is built to find its width
-    expect(callbackTracker, equals(<int>[0, 1, 2, 3, 4, 5]));
+    expect(callbackTracker, equals(<int>[0, 1, 2, 3, 4, 5, 6, 7]));
 
     callbackTracker.clear();
 
     final ScrollableState scrollable = tester.state(find.byType(Scrollable));
-    scrollable.position.jumpTo(400.0); // now only 4 should fit, numbered 2-5.
+    scrollable.position.jumpTo(600.0); // now only 4 should fit, numbered 2-5.
 
     await tester.pumpWidget(builder());
 
     // We build the visible children to find their new size.
-    expect(callbackTracker, equals(<int>[1, 2, 3, 4, 5]));
+    expect(callbackTracker, equals(<int>[1, 2, 3, 4, 5, 6, 7, 8]));
     callbackTracker.clear();
 
     await tester.pumpWidget(builder());
 
     // 0 isn't built because they're not visible.
-    expect(callbackTracker, equals(<int>[1, 2, 3, 4, 5]));
+    expect(callbackTracker, equals(<int>[1, 2, 3, 4, 5, 6, 7, 8]));
     callbackTracker.clear();
   });
 
@@ -189,18 +207,24 @@ void main() {
 
     await tester.pumpWidget(builder());
 
-    expect(callbackTracker, equals(<int>[0, 1, 2]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, 2,
+      3, // in cached area
+    ]));
     callbackTracker.clear();
     tester.allWidgets.forEach(collectText);
-    expect(text, equals(<String>['0', '1', '2']));
+    expect(text, equals(<String>['0', '1', '2', '3']));
     text.clear();
 
     await tester.pumpWidget(builder());
 
-    expect(callbackTracker, equals(<int>[0, 1, 2]));
+    expect(callbackTracker, equals(<int>[
+      0, 1, 2,
+      3, // in cached area
+    ]));
     callbackTracker.clear();
     tester.allWidgets.forEach(collectText);
-    expect(text, equals(<String>['0', '1', '2']));
+    expect(text, equals(<String>['0', '1', '2', '3']));
     text.clear();
   });
 
@@ -308,9 +332,10 @@ void main() {
         ' │   GrowthDirection.forward, ScrollDirection.idle, scrollOffset:\n'
         ' │   0.0, remainingPaintExtent: 600.0, crossAxisExtent: 800.0,\n'
         ' │   crossAxisDirection: AxisDirection.right,\n'
-        ' │   viewportMainAxisExtent: 600.0)\n'
+        ' │   viewportMainAxisExtent: 600.0, remainingCacheExtent: 850.0\n'
+        ' │   cacheOrigin: 0.0 )\n'
         ' │ geometry: SliverGeometry(scrollExtent: 300.0, paintExtent: 300.0,\n'
-        ' │   maxPaintExtent: 300.0)\n'
+        ' │   maxPaintExtent: 300.0, cacheExtent: 300.0)\n'
         ' │ currently live children: 0 to 2\n'
         ' │\n'
         ' ├─child with index 0: RenderRepaintBoundary#00000 relayoutBoundary=up2\n'

packages/flutter/test/widgets/nested_scroll_view_test.dart

@@ -339,7 +339,7 @@ void main() {
     final Offset point1 = tester.getCenter(find.text('AA'));
     await tester.dragFrom(point1, const Offset(0.0, 200.0));
     await tester.pump(const Duration(milliseconds: 20));
-    final Offset point2 = tester.getCenter(find.text('AA'));
+    final Offset point2 = tester.getCenter(find.text('AA', skipOffstage: false));
     expect(point1.dy, greaterThan(point2.dy));
   });
 
@@ -646,4 +646,4 @@ class TestHeader extends SliverPersistentHeaderDelegate {
   }
   @override
   bool shouldRebuild(TestHeader oldDelegate) => false;
-}
+}
\ No newline at end of file

packages/flutter/test/widgets/page_view_test.dart

@@ -257,7 +257,7 @@ void main() {
       ),
     ));
 
-    expect(find.text('Alabama'), findsOneWidget);
+    expect(find.text('Alabama', skipOffstage: false), findsOneWidget);
 
     await tester.pumpWidget(new Directionality(
       textDirection: TextDirection.ltr,

packages/flutter/test/widgets/scrollable_semantics_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:ui';
+
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/rendering.dart';
@@ -362,6 +364,12 @@ void main() {
                   label: r'item 1',
                   textDirection: TextDirection.ltr,
                 ),
+                new TestSemantics(
+                  flags: <SemanticsFlag>[
+                    SemanticsFlag.isHidden,
+                  ],
+                  label: r'item 2',
+                ),
               ],
             ),
           ],

packages/flutter/test/widgets/sliver_prototype_item_extent_test.dart

@@ -131,7 +131,7 @@ void main() {
     );
 
     // Item 0 exists in the list and as the prototype item.
-    expect(tester.widgetList(find.text('Item 0')).length, 2);
+    expect(tester.widgetList(find.text('Item 0', skipOffstage: false)).length, 2);
 
     for (int i = 1; i < 10; i += 1)
       expect(find.text('Item $i'), findsOneWidget);