fix a _ScaffoldLayout delegate update bug (#104954)

Author: xu-baolin

packages/flutter/lib/src/material/scaffold.dart

@@ -1144,12 +1144,13 @@ class _ScaffoldLayout extends MultiChildLayoutDelegate {
   @override
   bool shouldRelayout(_ScaffoldLayout oldDelegate) {
     return oldDelegate.minInsets != minInsets
-        || oldDelegate.textDirection != textDirection
-        || oldDelegate.floatingActionButtonMoveAnimationProgress != floatingActionButtonMoveAnimationProgress
-        || oldDelegate.previousFloatingActionButtonLocation != previousFloatingActionButtonLocation
-        || oldDelegate.currentFloatingActionButtonLocation != currentFloatingActionButtonLocation
-        || oldDelegate.extendBody != extendBody
-        || oldDelegate.extendBodyBehindAppBar != extendBodyBehindAppBar;
+      || oldDelegate.minViewPadding != minViewPadding
+      || oldDelegate.textDirection != textDirection
+      || oldDelegate.floatingActionButtonMoveAnimationProgress != floatingActionButtonMoveAnimationProgress
+      || oldDelegate.previousFloatingActionButtonLocation != previousFloatingActionButtonLocation
+      || oldDelegate.currentFloatingActionButtonLocation != currentFloatingActionButtonLocation
+      || oldDelegate.extendBody != extendBody
+      || oldDelegate.extendBodyBehindAppBar != extendBodyBehindAppBar;
   }
 }
 
@@ -2861,7 +2862,7 @@ class ScaffoldState extends State<Scaffold> with TickerProviderStateMixin, Resto
     // The minimum viewPadding for interactive elements positioned by the
     // Scaffold to keep within safe interactive areas.
     final EdgeInsets minViewPadding = mediaQuery.viewPadding.copyWith(
-      bottom: _resizeToAvoidBottomInset &&  mediaQuery.viewInsets.bottom != 0.0 ? 0.0 : null,
+      bottom: _resizeToAvoidBottomInset && mediaQuery.viewInsets.bottom != 0.0 ? 0.0 : null,
     );
 
     // extendBody locked when keyboard is open

packages/flutter/test/material/scaffold_test.dart

@@ -276,12 +276,17 @@ void main() {
     await tester.pumpWidget(
       MediaQuery(
         data: const MediaQueryData(
-          padding: EdgeInsets.only(bottom: 20.0),
+          viewPadding: EdgeInsets.only(bottom: 20.0),
         ),
         child: child,
       ),
     );
     final Offset initialPoint = tester.getCenter(find.byType(Placeholder));
+    expect(
+      tester.getBottomLeft(find.byType(Placeholder)).dy,
+      moreOrLessEquals(600.0 - 20.0 - kFloatingActionButtonMargin)
+    );
+
     // Consume bottom padding - as if by the keyboard opening
     await tester.pumpWidget(
       MediaQuery(
@@ -296,6 +301,37 @@ void main() {
     expect(initialPoint, finalPoint);
   });
 
+  testWidgets('viewPadding change should trigger _ScaffoldLayout re-layout', (WidgetTester tester) async {
+    Widget buildFrame(EdgeInsets viewPadding) {
+      return MediaQuery(
+        data: MediaQueryData(
+          viewPadding: viewPadding,
+        ),
+        child: Directionality(
+          textDirection: TextDirection.ltr,
+          child: Scaffold(
+            resizeToAvoidBottomInset: false,
+            body: Container(),
+            floatingActionButton: const Placeholder(),
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildFrame(const EdgeInsets.only(bottom: 300)));
+
+    final RenderBox renderBox = tester.renderObject<RenderBox>(find.byType(CustomMultiChildLayout));
+    expect(renderBox.debugNeedsLayout, false);
+
+    await tester.pumpWidget(
+      buildFrame(const EdgeInsets.only(bottom: 400)),
+      null,
+      EnginePhase.build,
+    );
+
+    expect(renderBox.debugNeedsLayout, true);
+  });
+
   testWidgets('Drawer scrolling', (WidgetTester tester) async {
     final Key drawerKey = UniqueKey();
     const double appBarHeight = 256.0;