Fix the NestedScrollView exception when rebuilding during scheduleWarmUpFrame (flutter#75308)

Author: xu-baolin

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

@@ -795,8 +795,13 @@ class _NestedScrollCoordinator implements ScrollActivityDelegate, ScrollHoldCont
 
   bool get hasScrolledBody {
     for (final _NestedScrollPosition position in _innerPositions) {
-      assert(position.hasContentDimensions && position.hasPixels);
-      if (position.pixels > position.minScrollExtent) {
+      if (!position.hasContentDimensions || !position.hasPixels) {
+        // It's possible that NestedScrollView built twice before layout phase
+        // in the same frame. This can happen when the FocusManager schedules a microTask
+        // that marks NestedScrollView dirty during the warm up frame.
+        // https://github.com/flutter/flutter/pull/75308
+        continue;
+      } else if (position.pixels > position.minScrollExtent) {
         return true;
       }
     }

packages/flutter/test/widgets/nested_scroll_view_test.dart

@@ -2303,6 +2303,49 @@ void main() {
 
     expect(lastUserScrollingDirection, ScrollDirection.forward);
   });
+
+  // Regression test for https://github.com/flutter/flutter/issues/72257
+  testWidgets('NestedScrollView works well when rebuilding during scheduleWarmUpFrame', (WidgetTester tester) async {
+    bool? isScrolled;
+    final Widget myApp = MaterialApp(
+      home: Scaffold(
+        body: StatefulBuilder(
+          builder: (BuildContext context, StateSetter setState) {
+            return Focus(
+              onFocusChange: (_) => setState( (){} ),
+              child: NestedScrollView(
+                headerSliverBuilder: (BuildContext context, bool boxIsScrolled) {
+                  isScrolled = boxIsScrolled;
+                  return <Widget>[
+                    const SliverAppBar(
+                      expandedHeight: 200,
+                      title: Text('Test'),
+                    )
+                  ];
+                },
+                body: CustomScrollView(
+                  slivers: <Widget>[
+                    SliverList(
+                      delegate: SliverChildBuilderDelegate(
+                        (BuildContext context, int index) {
+                          return const Text('');
+                        },
+                        childCount: 10,
+                      ),
+                    )
+                  ],
+                ),
+              ),
+            );
+          },
+        ),
+      ),
+    );
+
+    await tester.pumpWidget(myApp, Duration.zero, EnginePhase.build);
+    expect(isScrolled, false);
+    expect(tester.takeException(), isNull);
+  });
 }
 
 class TestHeader extends SliverPersistentHeaderDelegate {