Dart Navigator給出NoSuchMethodError

Question

我需要幫助，我試圖按下按鈕時顯示一個新頁面。我得到以下錯誤：

I/flutter (31562): The following NoSuchMethodError was thrown while handling a gesture: 
I/flutter (31562): Class 'MyHomePage' has no instance getter 'context'. 
I/flutter (31562): Receiver: Instance of 'MyHomePage' 
I/flutter (31562): Tried calling: context 
I/flutter (31562): When the exception was thrown, this was the stack: 

這裏是我的代碼：

import 'dart:convert'; 
import 'package:flutter/material.dart'; 
import 'package:flutter/services.dart'; 

class MyHomePage extends StatelessWidget{ 

    Container pictureSection(){ 
    return new Container(
     child: new Image.asset(
     'images/sw.jpeg', 
     width: 600.0, 
     height: 240.0, 
     fit: BoxFit.cover, 
    ), 
    ); 
    } 

    Container mainMenuSection(){ 
    var spacer = new SizedBox(height: 12.0); 
    return new Container(
     child: new Column(
     children: <Widget>[ 
      spacer, 
      new RaisedButton(
      onPressed:() {Navigator.of(context).pushNamed('/PlanetsPage');}, 
      child: new Text('Get Planet'), 
      ), 
      spacer, 
      ], 
     ), 
    ); 
    } 

    @override 
    Widget build(BuildContext context){ 
    var spacer = new SizedBox(height: 32.0); 
    var spacer2 = new SizedBox(height: 15.0); 
    return new Scaffold(
     body: new Center(
     child: new Column(
      children: <Widget>[ 
      pictureSection(), 
      mainMenuSection(), 
      ], 
     ), 
    ), 
    ); 
    } 
} 

class PlanetsPage extends StatelessWidget{ 
    Widget build(BuildContext context){ 
    return new Scaffold(
     body: new Center(
     child: new Column(
      child: new Text('Hello World'), 
     ), 
    ), 
    ); 
    } 
} 

void main(){ 
    runApp(new MaterialApp(
    home: new MyHomePage(), 
    routes: <String, WidgetBuilder> { 
     '/PlanetsPage': (BuildContext context) => new PlanetsPage(), 
    }, 
)); 
} 

我想，當按下按鈕從主頁去行星頁面，並且錯誤只能說明當我按下按鈕時。我正在使用我的Hauwei Nova進行測試。

Answer 1

嘗試從build方法中通過BuildContext而不是使用MyHomePage的context成員。見下：

import 'dart:convert'; 
import 'package:flutter/material.dart'; 
import 'package:flutter/services.dart'; 

class MyHomePage extends StatelessWidget{ 

    Container pictureSection(){ 
    return new Container(
     child: new Image.asset(
     'images/sw.jpeg', 
     width: 600.0, 
     height: 240.0, 
     fit: BoxFit.cover, 
    ), 
    ); 
    } 

    Container mainMenuSection(BuildContext context){ 
    var spacer = new SizedBox(height: 12.0); 
    return new Container(
     child: new Column(
     children: <Widget>[ 
      spacer, 
      new RaisedButton(
      onPressed:() {Navigator.of(context).pushNamed('/PlanetsPage');}, 
      child: new Text('Get Planet'), 
      ), 
      spacer, 
      ], 
     ), 
    ); 
    } 

    @override 
    Widget build(BuildContext context){ 
    var spacer = new SizedBox(height: 32.0); 
    var spacer2 = new SizedBox(height: 15.0); 
    return new Scaffold(
     body: new Center(
     child: new Column(
      children: <Widget>[ 
      pictureSection(), 
      mainMenuSection(context), 
      ], 
     ), 
    ), 
    ); 
    } 
} 

class PlanetsPage extends StatelessWidget{ 
    Widget build(BuildContext context){ 
    return new Scaffold(
     body: new Center(
     child: new Column(
      child: new Text('Hello World'), 
     ), 
    ), 
    ); 
    } 
} 

void main(){ 
    runApp(new MaterialApp(
    home: new MyHomePage(), 
    routes: <String, WidgetBuilder> { 
     '/PlanetsPage': (BuildContext context) => new PlanetsPage(), 
    }, 
)); 
}