向命名路由传递参数

Navigator 提供了从应用程序的任何部分使用通用标识符导航到命名路由的功能。在某些情况下，您可能还需要向命名路由传递参数。例如，您可能希望导航到 /user 路由并将用户信息传递到该路由。

您可以使用 Navigator.pushNamed() 方法的 arguments 参数来完成此任务。使用 ModalRoute.of() 方法或在提供给 MaterialApp 或 CupertinoApp 构造函数的 onGenerateRoute() 函数中提取参数。

此示例演示了如何向命名路由传递参数，以及如何使用以下步骤使用 ModalRoute.of() 和 onGenerateRoute() 读取参数

1. 定义需要传递的参数。
2. 创建一个提取参数的小部件。
3. 在 routes 表中注册小部件。
4. 导航到小部件。

首先，定义需要传递到新路由的参数。在本例中，传递两条数据：屏幕的 title 和 message。

要传递这两条数据，请创建一个存储这些信息的类。

// You can pass any object to the arguments parameter.
// In this example, create a class that contains both
// a customizable title and message.
class ScreenArguments {
  final String title;
  final String message;

  ScreenArguments(this.title, this.message);
}

接下来，创建一个提取并显示 ScreenArguments 中的 title 和 message 的小部件。要访问 ScreenArguments，请使用 ModalRoute.of() 方法。此方法返回带有参数的当前路由。

// A Widget that extracts the necessary arguments from
// the ModalRoute.
class ExtractArgumentsScreen extends StatelessWidget {
  const ExtractArgumentsScreen({super.key});

  static const routeName = '/extractArguments';

  @override
  Widget build(BuildContext context) {
    // Extract the arguments from the current ModalRoute
    // settings and cast them as ScreenArguments.
    final args = ModalRoute.of(context)!.settings.arguments as ScreenArguments;

    return Scaffold(
      appBar: AppBar(
        title: Text(args.title),
      ),
      body: Center(
        child: Text(args.message),
      ),
    );
  }
}

接下来，向提供给 MaterialApp 小部件的 routes 添加一个条目。routes 定义了根据路由名称应该创建哪个小部件。

MaterialApp(
  routes: {
    ExtractArgumentsScreen.routeName: (context) =>
        const ExtractArgumentsScreen(),
  },
)

最后，当用户点击按钮使用 Navigator.pushNamed() 时，导航到 ExtractArgumentsScreen。通过 arguments 属性向路由提供参数。ExtractArgumentsScreen 从这些参数中提取 title 和 message。

// A button that navigates to a named route.
// The named route extracts the arguments
// by itself.
ElevatedButton(
  onPressed: () {
    // When the user taps the button,
    // navigate to a named route and
    // provide the arguments as an optional
    // parameter.
    Navigator.pushNamed(
      context,
      ExtractArgumentsScreen.routeName,
      arguments: ScreenArguments(
        'Extract Arguments Screen',
        'This message is extracted in the build method.',
      ),
    );
  },
  child: const Text('Navigate to screen that extracts arguments'),
),

除了直接在小部件内部提取参数外，您还可以在一个 onGenerateRoute() 函数中提取参数并将它们传递给小部件。

onGenerateRoute() 函数根据给定的 RouteSettings 创建正确的路由。

MaterialApp(
  // Provide a function to handle named routes.
  // Use this function to identify the named
  // route being pushed, and create the correct
  // Screen.
  onGenerateRoute: (settings) {
    // If you push the PassArguments route
    if (settings.name == PassArgumentsScreen.routeName) {
      // Cast the arguments to the correct
      // type: ScreenArguments.
      final args = settings.arguments as ScreenArguments;

      // Then, extract the required data from
      // the arguments and pass the data to the
      // correct screen.
      return MaterialPageRoute(
        builder: (context) {
          return PassArgumentsScreen(
            title: args.title,
            message: args.message,
          );
        },
      );
    }
    // The code only supports
    // PassArgumentsScreen.routeName right now.
    // Other values need to be implemented if we
    // add them. The assertion here will help remind
    // us of that higher up in the call stack, since
    // this assertion would otherwise fire somewhere
    // in the framework.
    assert(false, 'Need to implement ${settings.name}');
    return null;
  },
)

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      routes: {
        ExtractArgumentsScreen.routeName: (context) =>
            const ExtractArgumentsScreen(),
      },
      // Provide a function to handle named routes.
      // Use this function to identify the named
      // route being pushed, and create the correct
      // Screen.
      onGenerateRoute: (settings) {
        // If you push the PassArguments route
        if (settings.name == PassArgumentsScreen.routeName) {
          // Cast the arguments to the correct
          // type: ScreenArguments.
          final args = settings.arguments as ScreenArguments;

          // Then, extract the required data from
          // the arguments and pass the data to the
          // correct screen.
          return MaterialPageRoute(
            builder: (context) {
              return PassArgumentsScreen(
                title: args.title,
                message: args.message,
              );
            },
          );
        }
        // The code only supports
        // PassArgumentsScreen.routeName right now.
        // Other values need to be implemented if we
        // add them. The assertion here will help remind
        // us of that higher up in the call stack, since
        // this assertion would otherwise fire somewhere
        // in the framework.
        assert(false, 'Need to implement ${settings.name}');
        return null;
      },
      title: 'Navigation with Arguments',
      home: const HomeScreen(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Home Screen'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            // A button that navigates to a named route.
            // The named route extracts the arguments
            // by itself.
            ElevatedButton(
              onPressed: () {
                // When the user taps the button,
                // navigate to a named route and
                // provide the arguments as an optional
                // parameter.
                Navigator.pushNamed(
                  context,
                  ExtractArgumentsScreen.routeName,
                  arguments: ScreenArguments(
                    'Extract Arguments Screen',
                    'This message is extracted in the build method.',
                  ),
                );
              },
              child: const Text('Navigate to screen that extracts arguments'),
            ),
            // A button that navigates to a named route.
            // For this route, extract the arguments in
            // the onGenerateRoute function and pass them
            // to the screen.
            ElevatedButton(
              onPressed: () {
                // When the user taps the button, navigate
                // to a named route and provide the arguments
                // as an optional parameter.
                Navigator.pushNamed(
                  context,
                  PassArgumentsScreen.routeName,
                  arguments: ScreenArguments(
                    'Accept Arguments Screen',
                    'This message is extracted in the onGenerateRoute '
                        'function.',
                  ),
                );
              },
              child: const Text('Navigate to a named that accepts arguments'),
            ),
          ],
        ),
      ),
    );
  }
}

// A Widget that extracts the necessary arguments from
// the ModalRoute.
class ExtractArgumentsScreen extends StatelessWidget {
  const ExtractArgumentsScreen({super.key});

  static const routeName = '/extractArguments';

  @override
  Widget build(BuildContext context) {
    // Extract the arguments from the current ModalRoute
    // settings and cast them as ScreenArguments.
    final args = ModalRoute.of(context)!.settings.arguments as ScreenArguments;

    return Scaffold(
      appBar: AppBar(
        title: Text(args.title),
      ),
      body: Center(
        child: Text(args.message),
      ),
    );
  }
}

// A Widget that accepts the necessary arguments via the
// constructor.
class PassArgumentsScreen extends StatelessWidget {
  static const routeName = '/passArguments';

  final String title;
  final String message;

  // This Widget accepts the arguments as constructor
  // parameters. It does not extract the arguments from
  // the ModalRoute.
  //
  // The arguments are extracted by the onGenerateRoute
  // function provided to the MaterialApp widget.
  const PassArgumentsScreen({
    super.key,
    required this.title,
    required this.message,
  });

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Text(message),
      ),
    );
  }
}

// You can pass any object to the arguments parameter.
// In this example, create a class that contains both
// a customizable title and message.
class ScreenArguments {
  final String title;
  final String message;

  ScreenArguments(this.title, this.message);
}

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