Remove MixedViewport

Also, port the MixedViewport tests to LazyBlockViewport. Fix bugs found by the tests.

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

@@ -1241,6 +1241,11 @@ class ErrorWidget extends LeafRenderObjectWidget {
 
   @override
   RenderBox createRenderObject(BuildContext context) => new RenderErrorBox(message);
+
+  @override
+  void debugFillDescription(List<String> description) {
+    description.add('message: ' + _stringify(message));
+  }
 }
 
 /// Base class for instantiations of widgets that have builders and can be

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

@@ -377,18 +377,8 @@ class _LazyBlockElement extends RenderObjectElement {
     renderObject.mainAxis = widget.mainAxis;
     LazyBlockDelegate newDelegate = newWidget.delegate;
     LazyBlockDelegate oldDelegate = oldWidget.delegate;
-    if (newDelegate != oldDelegate && (newDelegate.runtimeType != oldDelegate.runtimeType || newDelegate.shouldRebuild(oldDelegate))) {
-      IndexedBuilder builder = newDelegate.buildItem;
-      List<Widget> widgets = <Widget>[];
-      for (int i = 0; i < widgets.length; ++i) {
-        int logicalIndex = _firstChildLogicalIndex + i;
-        Widget childWidget = builder(this, logicalIndex);
-        if (childWidget == null)
-          break;
-        widgets[i] = new RepaintBoundary.wrap(childWidget, logicalIndex);
-      }
-      _children = new List<Element>.from(updateChildren(_children, widgets));
-    }
+    if (newDelegate != oldDelegate && (newDelegate.runtimeType != oldDelegate.runtimeType || newDelegate.shouldRebuild(oldDelegate)))
+      performRebuild();
     // If the new start offset can be displayed properly with the items
     // currently represented in _children, we just need to update the paint
     // offset. Otherwise, we need to trigger a layout in order to change the
@@ -405,6 +395,21 @@ class _LazyBlockElement extends RenderObjectElement {
     super.unmount();
   }
 
+  @override
+  void performRebuild() {
+    IndexedBuilder builder = widget.delegate.buildItem;
+    List<Widget> widgets = <Widget>[];
+    for (int i = 0; i < _children.length; ++i) {
+      int logicalIndex = _firstChildLogicalIndex + i;
+      Widget childWidget = builder(this, logicalIndex);
+      if (childWidget == null)
+        break;
+      widgets.add(new RepaintBoundary.wrap(childWidget, logicalIndex));
+    }
+    _children = new List<Element>.from(updateChildren(_children, widgets));
+    super.performRebuild();
+  }
+
   void _layout(BoxConstraints constraints) {
     final double blockExtent = _getMainAxisExtent(renderObject.size);
 

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

@@ -13,7 +13,6 @@ import 'package:flutter/rendering.dart' show HasMainAxis;
 import 'basic.dart';
 import 'framework.dart';
 import 'gesture_detector.dart';
-import 'mixed_viewport.dart';
 import 'notification_listener.dart';
 import 'page_storage.dart';
 import 'scroll_behavior.dart';
@@ -612,11 +611,10 @@ abstract class ScrollableState<T extends Scrollable> extends State<T> {
   /// The widgets used by this method should be widgets that provide a
   /// layout-time callback that reports the sizes that are relevant to
   /// the scroll offset (typically the size of the scrollable
-  /// container and the scrolled contents). [Viewport] and
-  /// [MixedViewport] provide an [onPaintOffsetUpdateNeeded] callback
-  /// for this purpose; [GridViewport], [ListViewport], and
-  /// [LazyListViewport] provide an [onExtentsChanged] callback for
-  /// this purpose.
+  /// container and the scrolled contents). [Viewport] provides an
+  /// [onPaintOffsetUpdateNeeded] callback for this purpose; [GridViewport],
+  /// [ListViewport], [LazyListViewport], and [LazyBlockViewport] provide an
+  /// [onExtentsChanged] callback for this purpose.
   ///
   /// This callback should be used to update the scroll behavior, if
   /// necessary, and then to call [updateGestureDetector] to update
@@ -705,6 +703,10 @@ class _ScrollableViewportState extends ScrollableState<ScrollableViewport> {
 /// A mashup of [ScrollableViewport] and [BlockBody]. Useful when you have a small,
 /// fixed number of children that you wish to arrange in a block layout and that
 /// might exceed the height of its container (and therefore need to scroll).
+///
+/// If you have a large number of children, consider using [LazyBlock] (if the
+/// children have variable height) or [ScrollableList] (if the children all have
+/// the same fixed height).
 class Block extends StatelessWidget {
   Block({
     Key key,
@@ -794,76 +796,3 @@ abstract class ScrollableListPainter extends RenderObjectPainter {
   /// or was canceled  by the user.
   Future<Null> scrollEnded() => new Future<Null>.value();
 }
-
-/// A general scrollable list for a large number of children that might not all
-/// have the same height. Prefer [ScrollableList] when all the children
-/// have the same height because it can use that property to be more efficient.
-/// Prefer [ScrollableViewport] with a single child.
-///
-/// ScrollableMixedWidgetList only supports vertical scrolling.
-class ScrollableMixedWidgetList extends Scrollable {
-  ScrollableMixedWidgetList({
-    Key key,
-    double initialScrollOffset,
-    ScrollListener onScroll,
-    SnapOffsetCallback snapOffsetCallback,
-    this.builder,
-    this.token,
-    this.onInvalidatorAvailable
-  }) : super(
-    key: key,
-    initialScrollOffset: initialScrollOffset,
-    onScroll: onScroll,
-    snapOffsetCallback: snapOffsetCallback
-  );
-
-  // TODO(ianh): Support horizontal scrolling.
-
-  final IndexedBuilder builder;
-  final Object token;
-  final InvalidatorAvailableCallback onInvalidatorAvailable;
-
-  @override
-  ScrollableMixedWidgetListState createState() => new ScrollableMixedWidgetListState();
-}
-
-class ScrollableMixedWidgetListState extends ScrollableState<ScrollableMixedWidgetList> {
-  @override
-  void initState() {
-    super.initState();
-    scrollBehavior.updateExtents(
-      contentExtent: double.INFINITY
-    );
-  }
-
-  @override
-  OverscrollBehavior createScrollBehavior() => new OverscrollBehavior();
-
-  @override
-  OverscrollBehavior get scrollBehavior => super.scrollBehavior;
-
-  Offset _handlePaintOffsetUpdateNeeded(ViewportDimensions dimensions) {
-    // We make various state changes here but don't have to do so in a
-    // setState() callback because we are called during layout and all
-    // we're updating is the new offset, which we are providing to the
-    // render object via our return value.
-    didUpdateScrollBehavior(scrollBehavior.updateExtents(
-      contentExtent: dimensions.contentSize.height,
-      containerExtent: dimensions.containerSize.height,
-      scrollOffset: scrollOffset
-    ));
-    updateGestureDetector();
-    return scrollOffsetToPixelDelta(scrollOffset);
-  }
-
-  @override
-  Widget buildContent(BuildContext context) {
-    return new MixedViewport(
-      startOffset: scrollOffset,
-      builder: config.builder,
-      token: config.token,
-      onInvalidatorAvailable: config.onInvalidatorAvailable,
-      onPaintOffsetUpdateNeeded: _handlePaintOffsetUpdateNeeded
-    );
-  }
-}

packages/flutter/lib/widgets.dart

@@ -27,7 +27,6 @@ export 'src/widgets/lazy_block.dart';
 export 'src/widgets/locale_query.dart';
 export 'src/widgets/media_query.dart';
 export 'src/widgets/mimic.dart';
-export 'src/widgets/mixed_viewport.dart';
 export 'src/widgets/modal_barrier.dart';
 export 'src/widgets/navigator.dart';
 export 'src/widgets/notification_listener.dart';

packages/flutter/test/widget/mixed_viewport_test.dart → packages/flutter/test/widget/lazy_block_viewport_test.dart

@@ -9,7 +9,7 @@ import 'package:test/test.dart';
 import 'test_widgets.dart';
 
 void main() {
-  test('MixedViewport mount/dismount smoke test', () {
+  test('LazyBlockViewport mount/dismount smoke test', () {
     testWidgets((WidgetTester tester) {
       List<int> callbackTracker = <int>[];
 
@@ -18,15 +18,15 @@ void main() {
 
       Widget builder() {
         return new FlipWidget(
-          left: new MixedViewport(
-            builder: (BuildContext context, int i) {
+          left: new LazyBlockViewport(
+            delegate: new LazyBlockBuilder(builder: (BuildContext context, int i) {
               callbackTracker.add(i);
               return new Container(
                 key: new ValueKey<int>(i),
                 height: 100.0,
                 child: new Text("$i")
               );
-            },
+            }),
             startOffset: 0.0
           ),
           right: new Text('Not Today')
@@ -54,7 +54,7 @@ void main() {
     });
   });
 
-  test('MixedViewport vertical', () {
+  test('LazyBlockViewport vertical', () {
     testWidgets((WidgetTester tester) {
       List<int> callbackTracker = <int>[];
 
@@ -76,8 +76,8 @@ void main() {
 
       Widget builder() {
         return new FlipWidget(
-          left: new MixedViewport(
-            builder: itemBuilder,
+          left: new LazyBlockViewport(
+            delegate: new LazyBlockBuilder(builder: itemBuilder),
             startOffset: offset
           ),
           right: new Text('Not Today')
@@ -86,23 +86,27 @@ void main() {
 
       tester.pumpWidget(builder());
 
-      // 0 is built to find its width
+      // 0 is built to find its height
       expect(callbackTracker, equals([0, 1, 2, 3, 4]));
-
       callbackTracker.clear();
 
       offset = 400.0; // now only 3 should fit, numbered 2-4.
 
       tester.pumpWidget(builder());
 
-      // 0 and 1 aren't built, we know their size and nothing else changed
-      expect(callbackTracker, equals([2, 3, 4]));
+      // We build all the children to find their new size.
+      expect(callbackTracker, equals([0, 1, 2, 3, 4]));
+      callbackTracker.clear();
+
+      tester.pumpWidget(builder());
 
+      // 0 isn't built because they're not visible.
+      expect(callbackTracker, equals([1, 2, 3, 4]));
       callbackTracker.clear();
     });
   });
 
-  test('MixedViewport horizontal', () {
+  test('LazyBlockViewport horizontal', () {
     testWidgets((WidgetTester tester) {
       List<int> callbackTracker = <int>[];
 
@@ -124,10 +128,10 @@ void main() {
 
       Widget builder() {
         return new FlipWidget(
-          left: new MixedViewport(
-            builder: itemBuilder,
+          left: new LazyBlockViewport(
+            delegate: new LazyBlockBuilder(builder: itemBuilder),
             startOffset: offset,
-            direction: Axis.horizontal
+            mainAxis: Axis.horizontal
           ),
           right: new Text('Not Today')
         );
@@ -144,14 +148,19 @@ void main() {
 
       tester.pumpWidget(builder());
 
-      // 0 and 1 aren't built, we know their size and nothing else changed
-      expect(callbackTracker, equals([2, 3, 4, 5]));
+      // We build all the children to find their new size.
+      expect(callbackTracker, equals([0, 1, 2, 3, 4, 5]));
+      callbackTracker.clear();
 
+      tester.pumpWidget(builder());
+
+      // 0 isn't built because they're not visible.
+      expect(callbackTracker, equals([1, 2, 3, 4, 5]));
       callbackTracker.clear();
     });
   });
 
-  test('MixedViewport reinvoke builders', () {
+  test('LazyBlockViewport reinvoke builders', () {
     testWidgets((WidgetTester tester) {
       List<int> callbackTracker = <int>[];
       List<String> text = <String>[];
@@ -173,8 +182,8 @@ void main() {
       };
 
       Widget builder() {
-        return new MixedViewport(
-          builder: itemBuilder,
+        return new LazyBlockViewport(
+          delegate: new LazyBlockBuilder(builder: itemBuilder),
           startOffset: 0.0
         );
       }
@@ -197,7 +206,7 @@ void main() {
     });
   });
 
-  test('MixedViewport reinvoke builders', () {
+  test('LazyBlockViewport reinvoke builders', () {
     testWidgets((WidgetTester tester) {
       StateSetter setState;
       ThemeData themeData = new ThemeData.light();
@@ -214,7 +223,9 @@ void main() {
         );
       };
 
-      Widget viewport = new MixedViewport(builder: itemBuilder);
+      Widget viewport = new LazyBlockViewport(
+        delegate: new LazyBlockBuilder(builder: itemBuilder)
+      );
 
       tester.pumpWidget(
         new StatefulBuilder(

packages/flutter/test/widget/scrollable_list_with_inherited_test.dart

@@ -28,7 +28,7 @@ Widget buildFrame() {
 }
 
 void main() {
-  test('MixedViewport is a build function (smoketest)', () {
+  test('LazyBlock is a build function (smoketest)', () {
     testWidgets((WidgetTester tester) {
       tester.pumpWidget(buildFrame());
       expect(tester.findText('0'), isNotNull);