应用程序随着时间的推移会累积数十个甚至数百个路由。您的一些路由可以作为顶级(全局)路由。例如,"/", "profile", "contact", "social_feed" 都可以是您应用内的顶级路由。但是,想象一下您在顶级的 Navigator widget 中定义了所有可能的路由。列表会非常长,而且许多这些路由最好嵌套在另一个 widget 中进行处理。

考虑一个用于您通过应用程序控制的无线灯泡的物联网 (IoT) 设置流程。此设置流程包含四个页面

  • find_devices 页面:查找附近的灯泡。
  • select_device 页面:选择要添加的灯泡。
  • connecting 页面:添加灯泡。
  • finished 页面:完成设置。

您可以从顶级的 Navigator widget orchestrate 此行为。但是,在 SetupFlow widget 中定义第二个嵌套的 Navigator widget 会更有意义,并让嵌套的 Navigator 负责设置流程中的四个页面。这种导航委托能够实现更强的本地控制,这在开发软件时通常是首选。

以下动画展示了应用程序的行为

Gif showing the nested "setup" flow

在本食谱中,您将实现一个四页的物联网设置流程,该流程将维护自己的导航,嵌套在顶级 Navigator widget 下方。

准备导航

#

此物联网应用程序有两个顶级屏幕以及设置流程。将这些路由名称定义为常量,以便可以在代码中引用它们。

dart
const routeHome = '/';
const routeSettings = '/settings';
const routePrefixDeviceSetup = '/setup/';
const routeDeviceSetupStart = '/setup/$routeDeviceSetupStartPage';
const routeDeviceSetupStartPage = 'find_devices';
const routeDeviceSetupSelectDevicePage = 'select_device';
const routeDeviceSetupConnectingPage = 'connecting';
const routeDeviceSetupFinishedPage = 'finished';

主屏幕和设置屏幕使用静态名称引用。但是,设置流程页面使用两个路径来创建它们的路由名称:一个 /setup/ 前缀后跟特定页面的名称。通过组合这两个路径,您的 Navigator 可以确定路由名称是用于设置流程的,而无需识别与设置流程关联的所有单个页面。

顶级 Navigator 不负责识别单独的设置流程页面。因此,您的顶级 Navigator 需要解析传入的路由名称以识别设置流程前缀。需要解析路由名称意味着您不能使用顶级 Navigatorroutes 属性。相反,您必须为 onGenerateRoute 属性提供一个函数。

实现 onGenerateRoute 以为三个顶级路径中的每一个返回适当的 widget。

dart
onGenerateRoute: (settings) {
  final Widget page;
  if (settings.name == routeHome) {
    page = const HomeScreen();
  } else if (settings.name == routeSettings) {
    page = const SettingsScreen();
  } else if (settings.name!.startsWith(routePrefixDeviceSetup)) {
    final subRoute = settings.name!.substring(
      routePrefixDeviceSetup.length,
    );
    page = SetupFlow(setupPageRoute: subRoute);
  } else {
    throw Exception('Unknown route: ${settings.name}');
  }

  return MaterialPageRoute<void>(
    builder: (context) {
      return page;
    },
    settings: settings,
  );
},

请注意,主屏幕和设置屏幕路由与精确的路由名称匹配。但是,设置流程路由条件仅检查前缀。如果路由名称包含设置流程前缀,则其余路由名称将被忽略并传递给 SetupFlow widget 进行处理。这种路由名称的分离允许顶级 Navigator 对设置流程中的各种子路由保持不可知。

创建一个名为 SetupFlow 的有状态 widget,它接受一个路由名称。

dart
class SetupFlow extends StatefulWidget {
  const SetupFlow({super.key, required this.setupPageRoute});

  final String setupPageRoute;

  @override
  State<SetupFlow> createState() => SetupFlowState();
}

class SetupFlowState extends State<SetupFlow> {
  //...
}

为设置流程显示应用栏

#

设置流程显示一个持久的应用栏,该应用栏会出现在所有页面上。

SetupFlow widget 的 build() 方法返回一个 Scaffold widget,并包含所需的 AppBar widget。

dart
@override
Widget build(BuildContext context) {
  return Scaffold(appBar: _buildFlowAppBar(), body: const SizedBox());
}

PreferredSizeWidget _buildFlowAppBar() {
  return AppBar(title: const Text('Bulb Setup'));
}

应用栏显示一个返回箭头,并在按下返回箭头时退出设置流程。但是,退出流程会导致用户丢失所有进度。因此,用户会被提示确认他们是否要退出设置流程。

提示用户确认退出设置流程,并确保在用户按下设备上的硬件返回按钮时显示提示。

dart
Future<void> _onExitPressed() async {
  final isConfirmed = await _isExitDesired();

  if (isConfirmed && mounted) {
    _exitSetup();
  }
}

Future<bool> _isExitDesired() async {
  return await showDialog<bool>(
        context: context,
        builder: (context) {
          return AlertDialog(
            title: const Text('Are you sure?'),
            content: const Text(
              'If you exit device setup, your progress will be lost.',
            ),
            actions: [
              TextButton(
                onPressed: () {
                  Navigator.of(context).pop(true);
                },
                child: const Text('Leave'),
              ),
              TextButton(
                onPressed: () {
                  Navigator.of(context).pop(false);
                },
                child: const Text('Stay'),
              ),
            ],
          );
        },
      ) ??
      false;
}

void _exitSetup() {
  Navigator.of(context).pop();
}

@override
Widget build(BuildContext context) {
  return PopScope(
    canPop: false,
    onPopInvokedWithResult: (didPop, _) async {
      if (didPop) return;

      if (await _isExitDesired() && context.mounted) {
        _exitSetup();
      }
    },
    child: Scaffold(appBar: _buildFlowAppBar(), body: const SizedBox()),
  );
}

PreferredSizeWidget _buildFlowAppBar() {
  return AppBar(
    leading: IconButton(
      onPressed: _onExitPressed,
      icon: const Icon(Icons.chevron_left),
    ),
    title: const Text('Bulb Setup'),
  );
}

当用户点击应用栏中的返回箭头,或按下设备上的返回按钮时,会弹出一个警报对话框,以确认用户是否要离开设置流程。如果用户按下 **Leave**,则设置流程会从顶级导航堆栈中弹出自身。如果用户按下 **Stay**,则操作将被忽略。

您可能会注意到 Navigator.pop() 同时被 **Leave** 和 **Stay** 按钮调用。需要明确的是,此 pop() 操作会从导航堆栈中弹出警报对话框,而不是设置流程。

生成嵌套路由

#

设置流程的职责是显示流程中相应的页面。

SetupFlow 添加一个 Navigator widget,并实现 onGenerateRoute 属性。

dart
final _navigatorKey = GlobalKey<NavigatorState>();

void _onDiscoveryComplete() {
  _navigatorKey.currentState!.pushNamed(routeDeviceSetupSelectDevicePage);
}

void _onDeviceSelected(String deviceId) {
  _navigatorKey.currentState!.pushNamed(routeDeviceSetupConnectingPage);
}

void _onConnectionEstablished() {
  _navigatorKey.currentState!.pushNamed(routeDeviceSetupFinishedPage);
}

@override
Widget build(BuildContext context) {
  return PopScope(
    canPop: false,
    onPopInvokedWithResult: (didPop, _) async {
      if (didPop) return;

      if (await _isExitDesired() && context.mounted) {
        _exitSetup();
      }
    },
    child: Scaffold(
      appBar: _buildFlowAppBar(),
      body: Navigator(
        key: _navigatorKey,
        initialRoute: widget.setupPageRoute,
        onGenerateRoute: _onGenerateRoute,
      ),
    ),
  );
}

Route<Widget> _onGenerateRoute(RouteSettings settings) {
  final page = switch (settings.name) {
    routeDeviceSetupStartPage => WaitingPage(
      message: 'Searching for nearby bulb...',
      onWaitComplete: _onDiscoveryComplete,
    ),
    routeDeviceSetupSelectDevicePage => SelectDevicePage(
      onDeviceSelected: _onDeviceSelected,
    ),
    routeDeviceSetupConnectingPage => WaitingPage(
      message: 'Connecting...',
      onWaitComplete: _onConnectionEstablished,
    ),
    routeDeviceSetupFinishedPage => FinishedPage(onFinishPressed: _exitSetup),
    _ => throw StateError('Unexpected route name: ${settings.name}!'),
  };

  return MaterialPageRoute(
    builder: (context) {
      return page;
    },
    settings: settings,
  );
}

_onGenerateRoute 函数的工作方式与顶级 Navigator 相同。将一个 RouteSettings 对象传递给函数,其中包含路由的 name。基于该路由名称,将返回四个流程页面中的一个。

第一个页面称为 find_devices,它会等待几秒钟以模拟网络扫描。等待期过后,该页面会调用其回调。在这种情况下,回调是 _onDiscoveryComplete。设置流程会识别出,在设备发现完成时,应该显示设备选择页面。因此,在 _onDiscoveryComplete 中,_navigatorKey 指示嵌套的 Navigator 导航到 select_device 页面。

select_device 页面要求用户从可用设备列表中选择一个设备。在本食谱中,只向用户呈现一个设备。当用户点击设备时,会调用 onDeviceSelected 回调。设置流程会识别出,当设备被选中时,应该显示连接页面。因此,在 _onDeviceSelected 中,_navigatorKey 指示嵌套的 Navigator 导航到 "connecting" 页面。

connecting 页面与 find_devices 页面的工作方式相同。connecting 页面等待几秒钟,然后调用其回调。在这种情况下,回调是 _onConnectionEstablished。设置流程会识别出,在建立连接后,应该显示最后一个页面。因此,在 _onConnectionEstablished 中,_navigatorKey 指示嵌套的 Navigator 导航到 finished 页面。

finished 页面为用户提供一个 **Finish** 按钮。当用户点击 **Finish** 时,会调用 _exitSetup 回调,该回调会将整个设置流程从顶级 Navigator 堆栈中弹出,将用户带回到主屏幕。

恭喜!您已实现了带有四个子路由的嵌套导航。

互动示例

#

运行应用

  • 在 **添加您的第一个灯泡** 屏幕上,点击 FAB(带有加号 **+** 的图标)。这将带您进入 **选择附近设备** 屏幕。列出了一个灯泡。
  • 点击列出的灯泡。会出现 **完成!** 屏幕。
  • 点击 **完成** 按钮返回到第一个屏幕。
import 'package:flutter/material.dart';

const routeHome = '/';
const routeSettings = '/settings';
const routePrefixDeviceSetup = '/setup/';
const routeDeviceSetupStart = '/setup/$routeDeviceSetupStartPage';
const routeDeviceSetupStartPage = 'find_devices';
const routeDeviceSetupSelectDevicePage = 'select_device';
const routeDeviceSetupConnectingPage = 'connecting';
const routeDeviceSetupFinishedPage = 'finished';

void main() {
  runApp(
    MaterialApp(
      theme: ThemeData(
        brightness: Brightness.dark,
        appBarTheme: const AppBarTheme(backgroundColor: Colors.blue),
        floatingActionButtonTheme: const FloatingActionButtonThemeData(
          backgroundColor: Colors.blue,
        ),
      ),
      onGenerateRoute: (settings) {
        final Widget page;
        if (settings.name == routeHome) {
          page = const HomeScreen();
        } else if (settings.name == routeSettings) {
          page = const SettingsScreen();
        } else if (settings.name!.startsWith(routePrefixDeviceSetup)) {
          final subRoute = settings.name!.substring(
            routePrefixDeviceSetup.length,
          );
          page = SetupFlow(setupPageRoute: subRoute);
        } else {
          throw Exception('Unknown route: ${settings.name}');
        }

        return MaterialPageRoute<void>(
          builder: (context) {
            return page;
          },
          settings: settings,
        );
      },
      debugShowCheckedModeBanner: false,
    ),
  );
}

@immutable
class SetupFlow extends StatefulWidget {
  static SetupFlowState of(BuildContext context) {
    return context.findAncestorStateOfType<SetupFlowState>()!;
  }

  const SetupFlow({super.key, required this.setupPageRoute});

  final String setupPageRoute;

  @override
  SetupFlowState createState() => SetupFlowState();
}

class SetupFlowState extends State<SetupFlow> {
  final _navigatorKey = GlobalKey<NavigatorState>();

  @override
  void initState() {
    super.initState();
  }

  void _onDiscoveryComplete() {
    _navigatorKey.currentState!.pushNamed(routeDeviceSetupSelectDevicePage);
  }

  void _onDeviceSelected(String deviceId) {
    _navigatorKey.currentState!.pushNamed(routeDeviceSetupConnectingPage);
  }

  void _onConnectionEstablished() {
    _navigatorKey.currentState!.pushNamed(routeDeviceSetupFinishedPage);
  }

  Future<void> _onExitPressed() async {
    final isConfirmed = await _isExitDesired();

    if (isConfirmed && mounted) {
      _exitSetup();
    }
  }

  Future<bool> _isExitDesired() async {
    return await showDialog<bool>(
          context: context,
          builder: (context) {
            return AlertDialog(
              title: const Text('Are you sure?'),
              content: const Text(
                'If you exit device setup, your progress will be lost.',
              ),
              actions: [
                TextButton(
                  onPressed: () {
                    Navigator.of(context).pop(true);
                  },
                  child: const Text('Leave'),
                ),
                TextButton(
                  onPressed: () {
                    Navigator.of(context).pop(false);
                  },
                  child: const Text('Stay'),
                ),
              ],
            );
          },
        ) ??
        false;
  }

  void _exitSetup() {
    Navigator.of(context).pop();
  }

  @override
  Widget build(BuildContext context) {
    return PopScope(
      canPop: false,
      onPopInvokedWithResult: (didPop, _) async {
        if (didPop) return;

        if (await _isExitDesired() && context.mounted) {
          _exitSetup();
        }
      },
      child: Scaffold(
        appBar: _buildFlowAppBar(),
        body: Navigator(
          key: _navigatorKey,
          initialRoute: widget.setupPageRoute,
          onGenerateRoute: _onGenerateRoute,
        ),
      ),
    );
  }

  Route<Widget> _onGenerateRoute(RouteSettings settings) {
    final page = switch (settings.name) {
      routeDeviceSetupStartPage => WaitingPage(
        message: 'Searching for nearby bulb...',
        onWaitComplete: _onDiscoveryComplete,
      ),
      routeDeviceSetupSelectDevicePage => SelectDevicePage(
        onDeviceSelected: _onDeviceSelected,
      ),
      routeDeviceSetupConnectingPage => WaitingPage(
        message: 'Connecting...',
        onWaitComplete: _onConnectionEstablished,
      ),
      routeDeviceSetupFinishedPage => FinishedPage(onFinishPressed: _exitSetup),
      _ => throw StateError('Unexpected route name: ${settings.name}!'),
    };

    return MaterialPageRoute(
      builder: (context) {
        return page;
      },
      settings: settings,
    );
  }

  PreferredSizeWidget _buildFlowAppBar() {
    return AppBar(
      leading: IconButton(
        onPressed: _onExitPressed,
        icon: const Icon(Icons.chevron_left),
      ),
      title: const Text('Bulb Setup'),
    );
  }
}

class SelectDevicePage extends StatelessWidget {
  const SelectDevicePage({super.key, required this.onDeviceSelected});

  final void Function(String deviceId) onDeviceSelected;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Padding(
          padding: const EdgeInsets.symmetric(horizontal: 24),
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              Text(
                'Select a nearby device:',
                style: Theme.of(context).textTheme.titleLarge,
              ),
              const SizedBox(height: 24),
              SizedBox(
                width: double.infinity,
                height: 54,
                child: ElevatedButton(
                  style: ButtonStyle(
                    backgroundColor: WidgetStateColor.resolveWith((states) {
                      return const Color(0xFF222222);
                    }),
                  ),
                  onPressed: () {
                    onDeviceSelected('22n483nk5834');
                  },
                  child: const Text(
                    'Bulb 22n483nk5834',
                    style: TextStyle(fontSize: 24),
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

class WaitingPage extends StatefulWidget {
  const WaitingPage({
    super.key,
    required this.message,
    required this.onWaitComplete,
  });

  final String message;
  final VoidCallback onWaitComplete;

  @override
  State<WaitingPage> createState() => _WaitingPageState();
}

class _WaitingPageState extends State<WaitingPage> {
  @override
  void initState() {
    super.initState();
    _startWaiting();
  }

  Future<void> _startWaiting() async {
    await Future<dynamic>.delayed(const Duration(seconds: 3));

    if (mounted) {
      widget.onWaitComplete();
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Padding(
          padding: const EdgeInsets.symmetric(horizontal: 24),
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              const CircularProgressIndicator(),
              const SizedBox(height: 32),
              Text(widget.message),
            ],
          ),
        ),
      ),
    );
  }
}

class FinishedPage extends StatelessWidget {
  const FinishedPage({super.key, required this.onFinishPressed});

  final VoidCallback onFinishPressed;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Padding(
          padding: const EdgeInsets.symmetric(horizontal: 24),
          child: SingleChildScrollView(
            child: Column(
              mainAxisSize: MainAxisSize.min,
              children: [
                Container(
                  width: 200,
                  height: 200,
                  decoration: const BoxDecoration(
                    shape: BoxShape.circle,
                    color: Color(0xFF222222),
                  ),
                  child: const Center(
                    child: Icon(
                      Icons.lightbulb,
                      size: 140,
                      color: Colors.white,
                    ),
                  ),
                ),
                const SizedBox(height: 32),
                const Text(
                  'Bulb added!',
                  textAlign: TextAlign.center,
                  style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
                ),
                const SizedBox(height: 32),
                ElevatedButton(
                  style: ButtonStyle(
                    padding: WidgetStateProperty.resolveWith((states) {
                      return const EdgeInsets.symmetric(
                        horizontal: 24,
                        vertical: 12,
                      );
                    }),
                    backgroundColor: WidgetStateColor.resolveWith((states) {
                      return const Color(0xFF222222);
                    }),
                    shape: WidgetStateProperty.resolveWith((states) {
                      return const StadiumBorder();
                    }),
                  ),
                  onPressed: onFinishPressed,
                  child: const Text('Finish', style: TextStyle(fontSize: 24)),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}

@immutable
class HomeScreen extends StatelessWidget {
  const HomeScreen({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: _buildAppBar(context),
      body: Center(
        child: Padding(
          padding: const EdgeInsets.symmetric(horizontal: 24),
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: [
              Container(
                width: 200,
                height: 200,
                decoration: const BoxDecoration(
                  shape: BoxShape.circle,
                  color: Color(0xFF222222),
                ),
                child: Center(
                  child: Icon(
                    Icons.lightbulb,
                    size: 140,
                    color: Theme.of(context).scaffoldBackgroundColor,
                  ),
                ),
              ),
              const SizedBox(height: 32),
              const Text(
                'Add your first bulb',
                textAlign: TextAlign.center,
                style: TextStyle(fontSize: 24, fontWeight: FontWeight.bold),
              ),
            ],
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () {
          Navigator.of(context).pushNamed(routeDeviceSetupStart);
        },
        child: const Icon(Icons.add),
      ),
    );
  }

  PreferredSizeWidget _buildAppBar(BuildContext context) {
    return AppBar(
      title: const Text('Welcome'),
      actions: [
        IconButton(
          icon: const Icon(Icons.settings),
          onPressed: () {
            Navigator.pushNamed(context, routeSettings);
          },
        ),
      ],
    );
  }
}

class SettingsScreen extends StatelessWidget {
  const SettingsScreen({super.key});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: _buildAppBar(),
      body: SingleChildScrollView(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: List.generate(8, (index) {
            return Container(
              width: double.infinity,
              height: 54,
              margin: const EdgeInsets.only(left: 16, right: 16, top: 16),
              decoration: BoxDecoration(
                borderRadius: BorderRadius.circular(8),
                color: const Color(0xFF222222),
              ),
            );
          }),
        ),
      ),
    );
  }

  PreferredSizeWidget _buildAppBar() {
    return AppBar(title: const Text('Settings'));
  }
}