Add PlatformSliverAppBar class with example

example/lib/platform_page.dart.dart

@@ -9,6 +9,7 @@ import 'logo.dart';
 import 'material_ios_page.dart';
 import 'platform_widget_example.dart';
 import 'tab_impl_page.dart';
+import 'sliver_app_bar_page.dart';
 
 class PlatformPage extends StatelessWidget {
   @override
@@ -385,6 +386,19 @@ class PlatformPage extends StatelessWidget {
               ),
             ),
           ),
+          // ! Platform Sliver AppBar
+          Padding(
+            padding: const EdgeInsets.all(8.0),
+            child: PlatformElevatedButton(
+              child: Text('Show  Sliver AppBar Page'),
+              onPressed: () => Navigator.of(context).push(
+                platformPageRoute(
+                  context: context,
+                  builder: (context) => PlatformSliverAppBarPage(),
+                ),
+              ),
+            ),
+          ),
           // ! Material on iOS
           if (isCupertino(context))
             Padding(

example/lib/sliver_app_bar_page.dart

@@ -0,0 +1,39 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_platform_widgets/flutter_platform_widgets.dart';
+
+class PlatformSliverAppBarPage extends StatefulWidget {
+  const PlatformSliverAppBarPage({super.key});
+
+  @override
+  State<PlatformSliverAppBarPage> createState() =>
+      _PlatformSliverAppBarPageState();
+}
+
+class _PlatformSliverAppBarPageState extends State<PlatformSliverAppBarPage> {
+  @override
+  Widget build(BuildContext context) {
+    return PlatformScaffold(
+      body: CustomScrollView(
+        slivers: <Widget>[
+          PlatformSliverAppBar(
+            title: Text('Sliver App Bar'),
+          ),
+          SliverList(
+            delegate: SliverChildBuilderDelegate(
+              (BuildContext context, int index) {
+                return Container(
+                  color: index.isOdd ? Colors.white : Colors.black12,
+                  height: 100.0,
+                  child: Center(
+                    child: PlatformText('$index', textScaleFactor: 5),
+                  ),
+                );
+              },
+              childCount: 20,
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}

lib/flutter_platform_widgets.dart

@@ -36,9 +36,10 @@ export 'src/platform_page_route.dart';
 export 'src/platform_popup_menu.dart';
 export 'src/platform_provider.dart';
 export 'src/platform_radio.dart';
-export 'src/platform_search_bar.dart';
 export 'src/platform_scaffold.dart';
+export 'src/platform_search_bar.dart';
 export 'src/platform_slider.dart';
+export 'src/platform_sliver_app_bar.dart';
 export 'src/platform_switch.dart';
 export 'src/platform_tab_scaffold.dart';
 export 'src/platform_text.dart';

lib/src/platform_sliver_app_bar.dart

@@ -0,0 +1,297 @@
+/*
+ * flutter_platform_widgets
+ * Copyright (c) 2018 Lance Johnstone. All rights reserved.
+ * See LICENSE for distribution and usage details.
+ */
+
+import 'package:flutter/cupertino.dart'
+    show CupertinoSliverNavigationBar, Brightness;
+import 'package:flutter/material.dart'
+    show SliverAppBar, kToolbarHeight; //MaterialStateProperty, ;
+import 'package:flutter/widgets.dart';
+import 'package:flutter/foundation.dart' show AsyncCallback;
+import 'package:flutter/services.dart' show SystemUiOverlayStyle;
+import 'platform.dart';
+import 'widget_base.dart';
+
+abstract class _BaseData {
+  _BaseData({
+    //Common
+    this.widgetKey,
+    this.leading,
+    this.automaticallyImplyLeading,
+    this.backgroundColor,
+    this.stretch,
+    this.title,
+  });
+
+  final Key? widgetKey;
+  final Widget? leading;
+  final bool? automaticallyImplyLeading;
+  final Color? backgroundColor;
+  final bool? stretch;
+  final Widget? title;
+}
+
+class MaterialSliverAppBarData extends _BaseData {
+  MaterialSliverAppBarData({
+    // Common
+    super.widgetKey,
+    super.leading,
+    super.automaticallyImplyLeading,
+    super.backgroundColor,
+    super.stretch,
+    super.title,
+
+    //Material
+    this.actions,
+    this.flexibleSpace,
+    this.bottom,
+    this.elevation,
+    this.scrolledUnderElevation,
+    this.shadowColor,
+    this.surfaceTintColor,
+    this.forceElevated = false,
+    this.foregroundColor,
+    this.iconTheme,
+    this.actionsIconTheme,
+    this.primary = true,
+    this.centerTitle,
+    this.excludeHeaderSemantics = false,
+    this.titleSpacing,
+    this.collapsedHeight,
+    this.expandedHeight,
+    this.floating = false,
+    this.pinned = false,
+    this.snap = false,
+    this.stretchTriggerOffset = 100.0,
+    this.onStretchTrigger,
+    this.shape,
+    this.toolbarHeight = kToolbarHeight,
+    this.leadingWidth,
+    this.toolbarTextStyle,
+    this.titleTextStyle,
+    this.systemOverlayStyle,
+    this.forceMaterialTransparency = false,
+    this.clipBehavior,
+  })  : assert(floating || !snap,
+            'The "snap" argument only makes sense for floating app bars.'),
+        assert(stretchTriggerOffset > 0.0),
+        assert(collapsedHeight == null || collapsedHeight >= toolbarHeight,
+            'The "collapsedHeight" argument has to be larger than or equal to [toolbarHeight].');
+
+  // final Widget? title;
+  final List<Widget>? actions;
+  final Widget? flexibleSpace;
+  final PreferredSizeWidget? bottom;
+  final double? elevation;
+  final double? scrolledUnderElevation;
+  final Color? shadowColor;
+  final Color? surfaceTintColor;
+  final bool forceElevated;
+  final Color? foregroundColor;
+  final IconThemeData? iconTheme;
+  final IconThemeData? actionsIconTheme;
+  final bool primary;
+  final bool? centerTitle;
+  final bool excludeHeaderSemantics;
+  final double? titleSpacing;
+  final double? collapsedHeight;
+  final double? expandedHeight;
+  final bool floating;
+  final bool pinned;
+  final ShapeBorder? shape;
+  final bool snap;
+  final double stretchTriggerOffset;
+  final AsyncCallback? onStretchTrigger;
+  final double toolbarHeight;
+  final double? leadingWidth;
+  final TextStyle? toolbarTextStyle;
+  final TextStyle? titleTextStyle;
+  final SystemUiOverlayStyle? systemOverlayStyle;
+  final bool forceMaterialTransparency;
+  final Clip? clipBehavior;
+}
+
+class CupertinoSliverAppBarData extends _BaseData {
+  CupertinoSliverAppBarData({
+    //Common
+    super.widgetKey,
+    super.leading,
+    super.automaticallyImplyLeading,
+    super.backgroundColor,
+    super.stretch,
+    super.title,
+
+    //Cupertino
+    // this.largeTitle,
+    this.automaticallyImplyTitle = true,
+    this.alwaysShowMiddle = true,
+    this.previousPageTitle,
+    this.middle,
+    this.trailing,
+    this.border = _kDefaultNavBarBorder,
+    this.brightness,
+    this.padding,
+    this.transitionBetweenRoutes = true,
+    this.heroTag = _defaultHeroTag,
+  }) : assert(
+          automaticallyImplyTitle == true || title != null,
+          'No title has been provided but automaticallyImplyTitle is also '
+          'false. Either provide a title or set automaticallyImplyTitle to '
+          'true.',
+        );
+
+  // final Widget? largeTitle;
+  final bool automaticallyImplyTitle;
+  final bool alwaysShowMiddle;
+  final String? previousPageTitle;
+  final Widget? middle;
+  final Widget? trailing;
+  final Brightness? brightness;
+  final EdgeInsetsDirectional? padding;
+  final Border? border;
+  final bool transitionBetweenRoutes;
+  final Object heroTag;
+}
+
+class PlatformSliverAppBar
+    extends PlatformWidgetBase<CupertinoSliverNavigationBar, SliverAppBar> {
+  //Common
+  final Key? widgetKey;
+
+  final Widget? leading;
+  final bool? automaticallyImplyLeading;
+  final Color? backgroundColor;
+  final bool? stretch;
+  final Widget? title;
+
+  //Platform
+  final PlatformBuilder<MaterialSliverAppBarData>? material;
+  final PlatformBuilder<CupertinoSliverAppBarData>? cupertino;
+
+  PlatformSliverAppBar({
+    //Common
+    super.key,
+    this.widgetKey,
+    this.leading,
+    this.automaticallyImplyLeading,
+    this.backgroundColor,
+    this.stretch,
+    this.title,
+    //Platform
+    this.material,
+    this.cupertino,
+  });
+
+  @override
+  SliverAppBar createMaterialWidget(BuildContext context) {
+    final data = material?.call(context, platform(context));
+    return SliverAppBar(
+      //Common
+      key: data?.widgetKey ?? widgetKey,
+      leading: data?.leading ?? leading,
+      automaticallyImplyLeading:
+          data?.automaticallyImplyLeading ?? automaticallyImplyLeading ?? true,
+      backgroundColor: data?.backgroundColor ?? backgroundColor,
+      stretch: data?.stretch ?? stretch ?? false,
+      title: data?.title ?? title,
+
+      //Material only
+      actions: data?.actions,
+      flexibleSpace: data?.flexibleSpace,
+      bottom: data?.bottom,
+      elevation: data?.elevation,
+      shadowColor: data?.shadowColor,
+      forceElevated: data?.forceElevated ?? false,
+      foregroundColor: data?.foregroundColor,
+      iconTheme: data?.iconTheme,
+      actionsIconTheme: data?.actionsIconTheme,
+      primary: data?.primary ?? true,
+      centerTitle: data?.centerTitle,
+      excludeHeaderSemantics: data?.excludeHeaderSemantics ?? false,
+      titleSpacing: data?.titleSpacing,
+      collapsedHeight: data?.collapsedHeight,
+      expandedHeight: data?.expandedHeight,
+      floating: data?.floating ?? false,
+      pinned: data?.pinned ?? false,
+      snap: data?.snap ?? false,
+      stretchTriggerOffset: data?.stretchTriggerOffset ?? 100.0,
+      onStretchTrigger: data?.onStretchTrigger,
+      shape: data?.shape,
+      toolbarHeight: data?.toolbarHeight ?? kToolbarHeight,
+      leadingWidth: data?.leadingWidth,
+      toolbarTextStyle: data?.toolbarTextStyle,
+      titleTextStyle: data?.titleTextStyle,
+      systemOverlayStyle: data?.systemOverlayStyle,
+      forceMaterialTransparency: data?.forceMaterialTransparency ?? false,
+      clipBehavior: data?.clipBehavior,
+    );
+  }
+
+  @override
+  CupertinoSliverNavigationBar createCupertinoWidget(BuildContext context) {
+    final data = cupertino?.call(context, platform(context));
+
+    return CupertinoSliverNavigationBar(
+      //Common
+      key: data?.widgetKey ?? widgetKey,
+      leading: data?.leading ?? leading,
+      automaticallyImplyLeading:
+          data?.automaticallyImplyLeading ?? automaticallyImplyLeading ?? true,
+      backgroundColor: data?.backgroundColor ?? backgroundColor,
+      stretch: data?.stretch ?? stretch ?? false,
+      largeTitle: data?.title ?? title,
+
+      //Cupertino only
+      automaticallyImplyTitle: data?.automaticallyImplyTitle ?? true,
+      alwaysShowMiddle: data?.alwaysShowMiddle ?? true,
+      previousPageTitle: data?.previousPageTitle,
+      middle: data?.middle,
+      trailing: data?.trailing,
+      border: data?.border ?? _kDefaultNavBarBorder,
+      brightness: data?.brightness,
+      padding: data?.padding,
+      transitionBetweenRoutes: data?.transitionBetweenRoutes ?? true,
+      heroTag: data?.heroTag ?? _defaultHeroTag,
+    );
+  }
+}
+
+//! Copied from file: /opt/homebrew/Caskroom/flutter/3.10.0/flutter/packages/flutter/lib/src/cupertino/nav_bar.dart
+const Color _kDefaultNavBarBorderColor = Color(0x4D000000);
+
+const Border _kDefaultNavBarBorder = Border(
+  bottom: BorderSide(
+    color: _kDefaultNavBarBorderColor,
+    width: 0.0, // 0.0 means one physical pixel
+  ),
+);
+
+const _HeroTag _defaultHeroTag = _HeroTag(null);
+
+@immutable
+class _HeroTag {
+  const _HeroTag(this.navigator);
+
+  final NavigatorState? navigator;
+
+  // Let the Hero tag be described in tree dumps.
+  @override
+  String toString() =>
+      'Default Hero tag for Cupertino navigation bars with navigator $navigator';
+
+  @override
+  bool operator ==(Object other) {
+    if (identical(this, other)) {
+      return true;
+    }
+    if (other.runtimeType != runtimeType) {
+      return false;
+    }
+    return other is _HeroTag && other.navigator == navigator;
+  }
+
+  @override
+  int get hashCode => identityHashCode(navigator);
+}