[material_3_demo] Refactor application code into multiple small libraries (#2581)

material_3_demo/lib/src/navigation_transition.dart

@@ -0,0 +1,79 @@
+// Copyright 2021 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+import 'bar_transition.dart';
+import 'component_screen.dart';
+import 'rail_transition.dart';
+
+class NavigationTransition extends StatefulWidget {
+  const NavigationTransition({
+    super.key,
+    required this.scaffoldKey,
+    required this.animationController,
+    required this.railAnimation,
+    required this.navigationRail,
+    required this.navigationBar,
+    required this.appBar,
+    required this.body,
+  });
+
+  final GlobalKey<ScaffoldState> scaffoldKey;
+  final AnimationController animationController;
+  final CurvedAnimation railAnimation;
+  final Widget navigationRail;
+  final Widget navigationBar;
+  final PreferredSizeWidget appBar;
+  final Widget body;
+
+  @override
+  State<NavigationTransition> createState() => _NavigationTransitionState();
+}
+
+class _NavigationTransitionState extends State<NavigationTransition> {
+  late final AnimationController controller;
+  late final CurvedAnimation railAnimation;
+  late final ReverseAnimation barAnimation;
+  bool controllerInitialized = false;
+  bool showDivider = false;
+
+  @override
+  void initState() {
+    super.initState();
+
+    controller = widget.animationController;
+    railAnimation = widget.railAnimation;
+
+    barAnimation = ReverseAnimation(
+      CurvedAnimation(parent: controller, curve: const Interval(0.0, 0.5)),
+    );
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final ColorScheme colorScheme = Theme.of(context).colorScheme;
+
+    return Scaffold(
+      key: widget.scaffoldKey,
+      appBar: widget.appBar,
+      body: Row(
+        children: <Widget>[
+          RailTransition(
+            animation: railAnimation,
+            backgroundColor: colorScheme.surface,
+            child: widget.navigationRail,
+          ),
+          widget.body,
+        ],
+      ),
+      bottomNavigationBar: BarTransition(
+        animation: barAnimation,
+        backgroundColor: colorScheme.surface,
+        child: widget.navigationBar,
+      ),
+      endDrawer: const NavigationDrawerSection(),
+    );
+  }
+}