跳至主要内容
内容

创建嵌套导航流程

内容

随着时间的推移，应用程序会积累数十甚至数百个路由。一些路由作为顶级（全局）路由是有意义的。例如，“/”、“profile”、“contact”、“social_feed”都是应用程序中可能的顶级路由。但是，假设您在顶级Navigator小部件中定义了所有可能的路由。列表将非常长，并且其中许多路由最好嵌套在另一个小部件中进行处理。

考虑一个用于无线灯泡的物联网 (IoT) 设置流程，您可以使用您的应用程序控制它。此设置流程包含 4 个页面：查找附近的灯泡、选择要添加的灯泡、添加灯泡，然后完成设置。您可以从顶级Navigator小部件协调此行为。但是，在SetupFlow小部件内定义第二个嵌套的Navigator小部件更有意义，并让嵌套的Navigator负责设置流程中的 4 个页面。这种导航委托促进了更大的本地控制，这在开发软件时通常是首选。

以下动画显示了应用程序的行为

Gif showing the nested "setup" flow

在本食谱中，您实现了一个四页的 IoT 设置流程，该流程在其自己的导航中保持嵌套在顶级Navigator小部件下方。

准备导航

#

此 IoT 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';

主页和设置屏幕使用静态名称引用。但是，设置流程页面使用两条路径来创建其路由名称：一个/setup/前缀，后跟特定页面的名称。通过组合这两条路径，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不负责识别单个设置流程页面。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无法使用顶级Navigator的routes属性。相反，您必须为onGenerateRoute属性提供一个函数。

实现onGenerateRoute以返回每个顶级路径的相应小部件。

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

请注意，主页和设置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，则忽略路由名称的其余部分并传递给SetupFlow小部件进行处理。这种路由名称的拆分允许顶级Navigator对设置流程内的各种子路由保持不可知。

创建一个名为SetupFlow的状态小部件，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性应用栏，该应用栏出现在所有页面上。

从SetupFlow小部件的build()方法返回一个Scaffold小部件，并包含所需的AppBar小部件。

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

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

应用栏显示一个后退箭头，并在按下后退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，系统会提示用户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 Android 上的硬件后退按钮时显示提示。

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后退箭头或按下 Android 上的后退按钮时，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“离开”，则设置流程会将其自身从顶级导航堆栈中弹出。如果用户按下“停留”，则忽略该操作。

您可能会注意到Navigator.pop()是由“离开”和“停留”按钮调用的。需要明确的是，此pop()操作会将警报对话框从导航堆栈中弹出，而不是设置流程。

生成嵌套路由

#

设置流程的工作是在流程中显示相应的页面。

将Navigator小部件添加到SetupFlow，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函数的工作原理与顶级Navigator相同。一个RouteSettings对象被传递到函数中，其中包括路由的name。根据该路由名称，将返回四个流程页面之一。

第一个页面称为find_devices，它等待几秒钟以模拟网络扫描。等待时间结束后，页面会调用其回调。在这种情况下，该回调为_onDiscoveryComplete。设置流程识别到，当设备发现完成后，应显示设备选择页面。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，仅向用户呈现一个设备。当用户点击设备时，会调用onDeviceSelected回调。设置流程识别到，当选择设备时，应显示连接页面。因此，在_onDeviceSelected中，_navigatorKey指示嵌套的Navigator导航到"connecting"页面。

connecting页面的工作方式与find_devices页面相同。connecting页面等待几秒钟，然后调用其回调。在这种情况下，回调为_onConnectionEstablished。设置流程识别到，当建立连接时，应显示最终页面。因此，在_onConnectionEstablished中，_navigatorKey指示嵌套的Navigator导航到finished页面。

finished页面为用户提供了一个“完成”按钮。当用户点击“完成”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，将用户带回主页。

恭喜！您使用四个子路由实现了嵌套导航。

交互式示例

#

运行应用程序

  • 在“添加您的第一个灯泡”屏幕上，点击 FAB（显示为加号“+”）。这将带您到“选择附近的设备”屏幕。列出了一个灯泡。
  • 点击列出的灯泡。“已完成！”屏幕出现。
  • 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<dynamic>(
          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'),
    );
  }
}

除非另有说明，否则本网站上的文档反映了 Flutter 的最新稳定版本。页面上次更新于 2024-10-14。 查看源代码 或 报告问题.