example: reference for #73

example/lib/menu_variable_height_front_layer.dart

@@ -0,0 +1,84 @@
+import 'package:backdrop/backdrop.dart';
+import 'package:flutter/material.dart';
+
+void main() => runApp(MyApp());
+
+/// Showcase for a Material Backdrop acting as a menu.
+class MyApp extends StatefulWidget {
+  @override
+  _MyAppState createState() => _MyAppState();
+}
+
+class _MyAppState extends State<MyApp> {
+  int _currentIndex = 0;
+
+  final List<Widget> _pages = [
+    _TallPage(),
+    ...List.generate(9, (i) => _ShortPage(i + 1)),
+  ];
+
+  final _nav = List.generate(
+      10,
+      (i) => ListTile(
+          title: Text('Menu: open page #$i',
+              style: TextStyle(color: Colors.white))));
+
+  double get _heightFactor => _currentIndex == 0 ? 1 : (.1 * _currentIndex);
+
+  @override
+  Widget build(BuildContext context) => MaterialApp(
+      title: 'Backdrop Demo',
+      home: BackdropScaffold(
+          appBar: BackdropAppBar(title: Text("AppBar is OK 👍")),
+          frontLayer: _pages[_currentIndex],
+          stickyFrontLayer: true,
+          backLayerScrim: Colors.red.withOpacity(0.5),
+          frontLayerScrim: Colors.green.withOpacity(0.5),
+          frontLayerActiveFactor: _heightFactor,
+          subHeader: BackdropSubHeader(title: Text('Subheader')),
+          backLayer: BackdropNavigationBackLayer(
+              items: _nav,
+              onTap: (int position) =>
+                  {setState(() => _currentIndex = position)},
+              separatorBuilder: (_, __) => _MyDivider())));
+}
+
+class _MyDivider extends StatelessWidget {
+  const _MyDivider();
+
+  @override
+  Widget build(BuildContext context) =>
+      Divider(indent: 16, endIndent: 16, color: Colors.white);
+}
+
+/// When the front layer doesn't have much content, its height while revealed
+/// is configurable via [BackdropScaffold.frontLayerActiveFactor].
+class _ShortPage extends StatelessWidget {
+  final int index;
+
+  _ShortPage(this.index);
+
+  @override
+  Widget build(BuildContext context) => Center(
+          child: Column(
+              mainAxisSize: MainAxisSize.min,
+              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
+              children: [
+            Text("Page #$index is open with desired height."),
+            const Flexible(child: FractionallySizedBox(heightFactor: 0.1)),
+            Text("It looks better! 😄"),
+            const Flexible(child: FractionallySizedBox(heightFactor: 0.1)),
+            Text("But Page #0 still needs to be tall."),
+          ]));
+}
+
+/// A front layer with a lot of content should reveal to show as much as possible.
+class _TallPage extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) => ListView(
+      children: List.generate(
+          20,
+          (index) => Padding(
+              padding: const EdgeInsets.all(16),
+              child: Text("Tall page #0, lots of content 👍"))));
+}