Add SliverGrid.builder constructor (#113116)

Author: gspencergoog

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

@@ -1757,13 +1757,14 @@ class GridView extends BoxScrollView {
   ///
   /// {@macro flutter.widgets.PageView.findChildIndexCallback}
   ///
-  /// The [gridDelegate] argument must not be null.
+  /// The [gridDelegate] argument is required.
   ///
   /// The `addAutomaticKeepAlives` argument corresponds to the
   /// [SliverChildBuilderDelegate.addAutomaticKeepAlives] property. The
   /// `addRepaintBoundaries` argument corresponds to the
-  /// [SliverChildBuilderDelegate.addRepaintBoundaries] property. Both must not
-  /// be null.
+  /// [SliverChildBuilderDelegate.addRepaintBoundaries] property. The
+  /// `addSemanticIndexes` argument corresponds to the
+  /// [SliverChildBuilderDelegate.addSemanticIndexes] property.
   GridView.builder({
     super.key,
     super.scrollDirection,

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

@@ -1166,6 +1166,49 @@ class SliverGrid extends SliverMultiBoxAdaptorWidget {
     required this.gridDelegate,
   });
 
+  /// A sliver that creates a 2D array of widgets that are created on demand.
+  ///
+  /// This constructor is appropriate for sliver grids with a large (or
+  /// infinite) number of children because the builder is called only for those
+  /// children that are actually visible.
+  ///
+  /// Providing a non-null `itemCount` improves the ability of the [SliverGrid]
+  /// to estimate the maximum scroll extent.
+  ///
+  /// `itemBuilder` will be called only with indices greater than or equal to
+  /// zero and less than `itemCount`.
+  ///
+  /// {@macro flutter.widgets.ListView.builder.itemBuilder}
+  ///
+  /// {@macro flutter.widgets.PageView.findChildIndexCallback}
+  ///
+  /// The [gridDelegate] argument is required.
+  ///
+  /// The `addAutomaticKeepAlives` argument corresponds to the
+  /// [SliverChildBuilderDelegate.addAutomaticKeepAlives] property. The
+  /// `addRepaintBoundaries` argument corresponds to the
+  /// [SliverChildBuilderDelegate.addRepaintBoundaries] property. The
+  /// `addSemanticIndexes` argument corresponds to the
+  /// [SliverChildBuilderDelegate.addSemanticIndexes] property.
+  SliverGrid.builder({
+    super.key,
+    required this.gridDelegate,
+    required NullableIndexedWidgetBuilder itemBuilder,
+    ChildIndexGetter? findChildIndexCallback,
+    int? itemCount,
+    bool addAutomaticKeepAlives = true,
+    bool addRepaintBoundaries = true,
+    bool addSemanticIndexes = true,
+  }) : assert(gridDelegate != null),
+       super(delegate: SliverChildBuilderDelegate(
+         itemBuilder,
+         findChildIndexCallback: findChildIndexCallback,
+         childCount: itemCount,
+         addAutomaticKeepAlives: addAutomaticKeepAlives,
+         addRepaintBoundaries: addRepaintBoundaries,
+         addSemanticIndexes: addSemanticIndexes,
+       ));
+
   /// Creates a sliver that places multiple box children in a two dimensional
   /// arrangement with a fixed number of tiles in the cross axis.
   ///

packages/flutter/test/widgets/slivers_test.dart

@@ -991,6 +991,45 @@ void main() {
     expect(firstTapped, 1);
     expect(secondTapped, 1);
   });
+
+  testWidgets('SliverGrid.builder can build children', (WidgetTester tester) async {
+    int firstTapped = 0;
+    int secondTapped = 0;
+    final Key key = UniqueKey();
+    await tester.pumpWidget(MaterialApp(
+      home: Scaffold(
+        key: key,
+        body: CustomScrollView(
+          slivers: <Widget>[
+            SliverGrid.builder(
+              itemCount: 2,
+              itemBuilder: (BuildContext context, int index) {
+                  return Material(
+                    color: index.isEven ? Colors.yellow : Colors.red,
+                    child: InkWell(
+                      onTap: () {
+                        index.isEven ? firstTapped++ : secondTapped++;
+                      },
+                      child: Text('Index $index'),
+                    ),
+                  );
+                },
+              gridDelegate: _TestArbitrarySliverGridDelegate(),
+            ),
+          ],
+        ),
+      ),
+    ));
+
+    // Verify correct hit testing
+    await tester.tap(find.text('Index 0'));
+    expect(firstTapped, 1);
+    expect(secondTapped, 0);
+    firstTapped = 0;
+    await tester.tap(find.text('Index 1'));
+    expect(firstTapped, 0);
+    expect(secondTapped, 1);
+  });
 }
 
 bool isRight(Offset a, Offset b) => b.dx > a.dx;