This PR is making the `CupertinoNavigationBar` and `CupertinoSliverNavigationBar` appear transparent as long as the content is not scrolled under them, so they look like standard iOS apps nav bars.
https://github.com/flutter/flutter/assets/423393/eee2700b-2a91-4577-922c-6163d47cb357https://github.com/flutter/flutter/assets/423393/3847f2b5-0dac-4d5e-aa6f-03c1d2893e30
<details>
<summary>Demo app code</summary>
```dart
import 'package:flutter/cupertino.dart';
/// Flutter code sample for [CupertinoTabScaffold].
void main() => runApp(const TabScaffoldApp());
class TabScaffoldApp extends StatefulWidget {
const TabScaffoldApp({super.key});
@override
State<TabScaffoldApp> createState() => _TabScaffoldAppState();
}
class _TabScaffoldAppState extends State<TabScaffoldApp> {
Brightness _brightness = Brightness.light;
@override
Widget build(BuildContext context) {
return CupertinoApp(
theme: CupertinoThemeData(brightness: _brightness),
home: TabScaffoldExample(
brightness: _brightness, onBrightnessToggle: _toggleBrightness),
);
}
void _toggleBrightness() {
setState(() {
_brightness =
_brightness == Brightness.light ? Brightness.dark : Brightness.light;
});
}
}
class TabScaffoldExample extends StatefulWidget {
const TabScaffoldExample(
{required this.brightness, required this.onBrightnessToggle, super.key});
final VoidCallback onBrightnessToggle;
final Brightness brightness;
@override
State<TabScaffoldExample> createState() => _TabScaffoldExampleState();
}
class _TabScaffoldExampleState extends State<TabScaffoldExample> {
@override
Widget build(BuildContext context) {
return CupertinoTabScaffold(
tabBar: CupertinoTabBar(
items: const <BottomNavigationBarItem>[
BottomNavigationBarItem(
icon: Icon(CupertinoIcons.home),
label: 'Home',
),
BottomNavigationBarItem(
icon: Icon(CupertinoIcons.search_circle_fill),
label: 'Explore',
),
BottomNavigationBarItem(
icon: Icon(CupertinoIcons.person_fill),
label: 'Profile',
),
BottomNavigationBarItem(
icon: Icon(CupertinoIcons.settings_solid),
label: 'Settings',
),
],
),
tabBuilder: (BuildContext context, int index) {
return CupertinoTabView(
builder: (BuildContext context) {
return CupertinoPageScaffold(
backgroundColor: index == 3
? CupertinoColors.secondarySystemBackground
.resolveFrom(context)
: null,
child: CustomScrollView(
slivers: [
CupertinoSliverNavigationBar(
largeTitle: Text('Tab $index'),
initiallyTransparent: index != 2,
trailing: CupertinoButton(
padding: EdgeInsets.zero,
onPressed: widget.onBrightnessToggle,
child: Icon(
widget.brightness == Brightness.light
? CupertinoIcons.moon_stars
: CupertinoIcons.sun_max,
),
),
),
SliverSafeArea(
top: false,
sliver: SliverList.list(
children: [
CupertinoButton(
child: const Text('Next page'),
onPressed: () {
Navigator.of(context).push(
CupertinoPageRoute<void>(
builder: (BuildContext context) {
return CupertinoPageScaffold(
navigationBar: CupertinoNavigationBar(
middle: Text('Inner page of tab $index'),
),
child: ListView(
children: [
Center(
child: CupertinoButton(
child: const Text('Back'),
onPressed: () {
Navigator.of(context).pop();
},
),
),
if (index == 0) const _LongList(),
const SizedBox(height: 20),
],
),
);
},
),
);
},
),
if (index == 1) const _LongList(),
const SizedBox(height: 20),
],
),
),
],
),
);
},
);
},
);
}
}
class _LongList extends StatelessWidget {
const _LongList();
@override
Widget build(BuildContext context) {
return Column(
children: [
for (int i = 0; i < 50; i++) ...[
CupertinoListTile(
leading: const Icon(CupertinoIcons.book),
title: Text('Bookstore item $i'),
),
],
],
);
}
}
```
</details>
This is the continuation of https://github.com/flutter/flutter/pull/142439.
I tried to keep the simplest API possible, so it's only introducing a new `automaticBackgroundVisibility` boolean parameter.
In the implementation I had to use the `CupertinoPageScaffold` background color to make it look transparent instead of a 0 opacity, because of issues with route transitions.
I used an `InheritedWidget` so the nav bar is always getting the right background color from the parent scaffold, whether it is overridden or not. It would probably be better to make the inherited widget private but we'd need to move all the nav bar code to the same file as the scaffold, so for now I've just hidden it from the export. Let me know if it is okay to do that.
This PR is not dealing with the bottom tab bar, because the same [straightforward approach](dde8ec6dc7) doesn't work here. The problem is that the scroll notification is sent only when the scroll view is created or updated, so it doesn't work if one pushes a screen and navigates back.
Issues:
- #78607
- #60411
This does a cleanup of the examples, removing all of the "section" markers and extra comments that we don't need anymore now that the samples are no longer in the source code. It also removes the --template arguments from the {@tool dartpad} and {@tool sample} directives, since those are no longer used. It converts two examples that I discovered were still embedded into linked examples in the examples folder.
I didn't delete the templates from the snippets config folder yet, because there are still embedded samples in the dart:ui package from the engine that use them. Once dart:ui no longer uses the templates, they can be removed.
I bumped the version of the snippets package to pick up a change that allows removal of the --template argument.
This extracts the sample code out from the API doc comments, and places them in separate files on disk, allowing running of the examples locally, testing them, and building of slightly larger examples.
