SliverAppBar Default Elevation Patch (#73526)

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

@@ -1154,7 +1154,7 @@ class _SliverAppBarDelegate extends SliverPersistentHeaderDelegate {
           ? Semantics(child: flexibleSpace, header: true)
           : flexibleSpace,
         bottom: bottom,
-        elevation: forceElevated || overlapsContent || (pinned && shrinkOffset > maxExtent - minExtent) ? elevation ?? 4.0 : 0.0,
+        elevation: forceElevated || overlapsContent || (pinned && shrinkOffset > maxExtent - minExtent) ? elevation : 0.0,
         shadowColor: shadowColor,
         backgroundColor: backgroundColor,
         foregroundColor: foregroundColor,

packages/flutter/test/material/app_bar_test.dart

@@ -903,30 +903,79 @@ void main() {
     expect(tabBarHeight(tester), initialTabBarHeight);
   });
 
-  testWidgets('SliverAppBar rebuilds when forceElevated changes', (WidgetTester tester) async {
-    // Regression test for https://github.com/flutter/flutter/issues/59158.
-    Widget buildSliverAppBar(bool forceElevated) {
+  testWidgets('AppBar uses the specified elevation or defaults to 4.0', (WidgetTester tester) async {
+    Widget buildAppBar([double? elevation]) {
       return MaterialApp(
+        home: Scaffold(
+          appBar: AppBar(title: const Text('Title'), elevation: elevation),
+        ),
+      );
+    }
+
+    Material getMaterial() => tester.widget<Material>(find.descendant(
+      of: find.byType(AppBar),
+      matching: find.byType(Material),
+    ));
+
+    // Default elevation should be _AppBarState._defaultElevation = 4.0
+    await tester.pumpWidget(buildAppBar());
+    expect(getMaterial().elevation, 4.0);
+
+    // AppBar should use the specified elevation.
+    await tester.pumpWidget(buildAppBar(8.0));
+    expect(getMaterial().elevation, 8.0);
+  });
+
+  group('SliverAppBar elevation', () {
+    Widget buildSliverAppBar(bool forceElevated, {double? elevation, double? themeElevation}) {
+      return MaterialApp(
+        theme: ThemeData(appBarTheme: AppBarTheme(elevation: themeElevation)),
         home: CustomScrollView(
           slivers: <Widget>[
             SliverAppBar(
               backwardsCompatibility: false,
               title: const Text('Title'),
               forceElevated: forceElevated,
+              elevation: elevation,
             ),
           ],
         ),
       );
     }
 
-    final Finder appBarFinder = find.byType(AppBar);
-    AppBar getAppBarWidget(Finder finder) => tester.widget<AppBar>(finder);
+    testWidgets('Respects forceElevated parameter', (WidgetTester tester) async {
+      // Regression test for https://github.com/flutter/flutter/issues/59158.
+      AppBar getAppBar() => tester.widget<AppBar>(find.byType(AppBar));
+      Material getMaterial() => tester.widget<Material>(find.byType(Material));
+
+      // When forceElevated is off, SliverAppBar should not be elevated.
+      await tester.pumpWidget(buildSliverAppBar(false));
+      expect(getMaterial().elevation, 0.0);
+
+      // Default elevation should be _AppBarState._defaultElevation = 4.0, and
+      // the AppBar's elevation should not be specified by SliverAppBar.
+      await tester.pumpWidget(buildSliverAppBar(true));
+      expect(getMaterial().elevation, 4.0);
+      expect(getAppBar().elevation, null);
 
-    await tester.pumpWidget(buildSliverAppBar(false));
-    expect(getAppBarWidget(appBarFinder).elevation, 0.0);
+      // SliverAppBar should use the specified elevation.
+      await tester.pumpWidget(buildSliverAppBar(true, elevation: 8.0));
+      expect(getMaterial().elevation, 8.0);
+    });
+
+    testWidgets('Uses elevation of AppBarTheme by default', (WidgetTester tester) async {
+      // Regression test for https://github.com/flutter/flutter/issues/73525.
+      Material getMaterial() => tester.widget<Material>(find.byType(Material));
+
+      await tester.pumpWidget(buildSliverAppBar(false, themeElevation: 12.0));
+      expect(getMaterial().elevation, 0.0);
 
-    await tester.pumpWidget(buildSliverAppBar(true));
-    expect(getAppBarWidget(appBarFinder).elevation, 4.0);
+      await tester.pumpWidget(buildSliverAppBar(true, themeElevation: 12.0));
+      expect(getMaterial().elevation, 12.0);
+
+      await tester.pumpWidget(buildSliverAppBar(true, elevation: 8.0, themeElevation: 12.0));
+      expect(getMaterial().elevation, 8.0);
+    });
   });
 
   testWidgets('AppBar dimensions, with and without bottom, primary', (WidgetTester tester) async {