Merge pull request #2796 from HansMuller/ali_demo

Fix _LazyWidgetProvider indexing, move Ali Connors

examples/material_gallery/lib/gallery/home.dart

@@ -17,6 +17,7 @@ import '../demo/date_picker_demo.dart';
 import '../demo/dialog_demo.dart';
 import '../demo/drop_down_demo.dart';
 import '../demo/fitness_demo.dart';
+import '../demo/flexible_space_demo.dart';
 import '../demo/grid_list_demo.dart';
 import '../demo/icons_demo.dart';
 import '../demo/leave_behind_demo.dart';
@@ -103,6 +104,7 @@ class GalleryHomeState extends State<GalleryHome> {
                 image: 'assets/section_components.png',
                 colors: Colors.amber,
                 demos: <GalleryDemo>[
+                  new GalleryDemo(title: 'App Bar', builder: () => new FlexibleSpaceDemo()),
                   new GalleryDemo(title: 'Buttons', builder: () => new ButtonsDemo()),
                   new GalleryDemo(title: 'Buttons: Floating Action Button', builder: () => new TabsFabDemo()),
                   new GalleryDemo(title: 'Cards', builder: () => new CardsDemo()),

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

@@ -297,7 +297,8 @@ class _LazyWidgetProvider extends _WidgetProvider {
 
   @override
   Widget getChild(int i) {
-    int n = _length ?? _widgets.length;
-    return _widgets[(i % n).abs()];
+    final int childCount = virtualChildCount;
+    final int index = childCount != null ? (i % childCount).abs() : i;
+    return _widgets[index - _base];
   }
 }

packages/flutter/test/widget/scrollable_lazy_list_test.dart

@@ -158,4 +158,51 @@ void main() {
       callbackTracker.clear();
     });
   });
+
+  test('ScrollableLazyList 10 items, 2-3 items visible', () {
+    testWidgets((WidgetTester tester) {
+      List<int> callbackTracker = <int>[];
+
+      // The root view is 800x600 in the test environment and our list
+      // items are 300 tall. Scrolling should cause two or three items
+      // to be built.
+
+      ItemListBuilder itemBuilder = (BuildContext context, int start, int count) {
+        List<Widget> result = <Widget>[];
+        for (int index = start; index < start + count; index += 1) {
+          callbackTracker.add(index);
+          result.add(new Text('$index', key: new ValueKey<int>(index)));
+        }
+        return result;
+      };
+
+      GlobalKey<ScrollableState<ScrollableLazyList>> scrollableKey = new GlobalKey<ScrollableState<ScrollableLazyList>>();
+      Widget testWidget = new ScrollableLazyList(
+        key: scrollableKey,
+        itemBuilder: itemBuilder,
+        itemExtent: 300.0,
+        itemCount: 10
+      );
+
+      tester.pumpWidget(testWidget);
+      expect(callbackTracker, equals([0, 1]));
+      callbackTracker.clear();
+
+      scrollableKey.currentState.scrollTo(150.0);
+      tester.pumpWidget(testWidget);
+      expect(callbackTracker, equals([0, 1, 2]));
+      callbackTracker.clear();
+
+      scrollableKey.currentState.scrollTo(600.0);
+      tester.pumpWidget(testWidget);
+      expect(callbackTracker, equals([2, 3]));
+      callbackTracker.clear();
+
+      scrollableKey.currentState.scrollTo(750.0);
+      tester.pumpWidget(testWidget);
+      expect(callbackTracker, equals([2, 3, 4]));
+      callbackTracker.clear();
+    });
+  });
+
 }