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我是编程和 Flutter 的新手。

在我的应用程序中，我构建了一个带有 int 变量的页面导航器。更改整数值后，我希望应用程序将用户路由到特定的指定页面。但是，我在按下时收到“匿名关闭”错误。

如果有人可以解释为什么我会收到此错误并发布此代码的更正版本，将不胜感激？

以下是调试器中的完整错误片段。

Reloaded 1 of 529 libraries in 885ms.
flutter: Page #1 Clicked

════════ Exception caught by gesture ═══════════════════════════════════════════
The following NoSuchMethodError was thrown while handling a gesture:
The method 'call' was called on null.
Receiver: null
Tried calling: call()

When the exception was thrown, this was the stack
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)
#1      _MyHomePageState.build.<anonymous closure>
package:navigator_test/main.dart:45
#2      _InkResponseState._handleTap
package:flutter/…/material/ink_well.dart:993
#3      _InkResponseState.build.<anonymous closure>
package:flutter/…/material/ink_well.dart:1111
#4      GestureRecognizer.invokeCallback
package:flutter/…/gestures/recognizer.dart:183
...
Handler: "onTap"
Recognizer: TapGestureRecognizer#5df0c
    debugOwner: GestureDetector
    state: possible
    won arena
    finalPosition: Offset(208.7, 509.7)
    finalLocalPosition: Offset(76.7, 19.7)
    button: 1
    sent tap down
════════════════════════════════════════════════════════════════════════════════

下面是导航器的示意图

import 'package:flutter/material.dart';
import 'package:navigator_test/main.dart';
import 'package:navigator_test/page1.dart';

class Navigator extends StatefulWidget {
  @override
  _NavigatorState createState() => _NavigatorState();
}

class _NavigatorState extends State<Navigator> {
  int nav = 0;

  void page1() {
    setState(() {
      nav = 1;
    });
  }

  @override
  Widget build(BuildContext context) {
    if (nav < 1) {
      return MyHomePage(page1: page1);
    } else if (nav < 2) {
      return Page1();
    } else {
      return null;
    }
  }
}

我正在主页上导入功能。

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  final Function page1;
  MyHomePage({this.page1});

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

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Navigation Test'),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            SizedBox(height: 20),
            FlatButton.icon(
              onPressed: () {
                print('Page #1 Clicked');
                widget.page1();
              },
              icon: Icon(Icons.add_shopping_cart),
              label: Text('Goto Page #1'),
            )
          ],
        ),
      ),
      // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}
4

1 回答 1

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您收到此错误是因为您MyHomePage直接在 MyApp 中调用，而没有传递参数 page1，因此当您按下“转到页面 #1”时，会调用一个空函数。要解决此问题，您可以改为在以下位置调用 Navigator MyApp：

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: Navigator(),
    );
  }
}

但是无需调用 setState 导航到新页面的主要方法是使用NavigatorFlutter 的类，如下所示（请记住先删除 Navigator 类，这样 IDE 就会知道您正在调用 Flutter 的 Navigator 类）：

onPressed: () {
  print('Page #1 Clicked');
  //push the new route, but allowing you to go back to the previous one
  Navigator.of(context).push(

    //Default page transition of android
    MaterialPageRoute(
      builder: (context) => Page1(),
    ),
  );
},

或者：

Navigator.of(context).push(
  //Default page transition of IOS
  CupertinoPageRoute(
    builder: (context) => Page1(),
  ),
);

有关更多信息，请参阅文档。

于 2021-02-20T13:46:22.807 回答