Flutterの画面遷移にて、Undefined name 'context'と表示されてしまう問題を解決したい

onTapのところでエラーが出てしまいます…。

flutter
1import 'package:flutter/material.dart';
2
3void main() {
4  runApp(MyApp());
5}
6class MyApp extends StatefulWidget {
7  @override
8  _FirstRouteState createState() => _FirstRouteState();
9}
10
11class _FirstRouteState extends State<MyApp> {
12  @override
13  Widget build(BuildContext context) {
14    return MaterialApp(
15      home: Scaffold(
16        appBar: AppBar(
17          title: const Text('StudySummary',
18            style: TextStyle(
19              fontWeight: FontWeight.bold,
20              fontStyle: FontStyle.italic,
21              fontSize: 18,
22            ),),
23        ),
24        body: ListView.builder(
25          itemBuilder: (BuildContext context, int index) {
26            return Padding(
27              padding: const EdgeInsets.only(top:8.0,left: 9.0),
28              child: EntryItem(data[index]),
29            );
30          },
31          itemCount: data.length,
32        ),
33      ),
34    );
35  }
36}
37class Entry {
38  Entry(this.title, [this.children = const <Entry>[]]);
39  final String title;
40  final List<Entry> children;
41}
42final List<Entry> data = <Entry>[
43  Entry(
44    '現代文',
45  ),
46  Entry(
47    '数学',
48  ),
49  Entry(
50    '英語',
51  ),
52  Entry(
53    '化学',
54  ),
55  Entry(
56    '物理',
57  ),
58  Entry(
59    '社会',
60  ),
61  Entry(
62    'その他',
63  ),
64];
65
66// Displays one Entry. If the entry has children then it's displayed
67// with an ExpansionTile.
68class EntryItem extends StatelessWidget {
69  const EntryItem(this.entry);
70
71  final Entry entry;
72//expansionリストの一番下にいる子供達
73
74  Widget _buildTiles(Entry root) {
75
76    if (root.children.isEmpty) return Padding(
77      padding: const EdgeInsets.only(left:18.0),
78      child: ListTile(
79
80        //leading: const Icon(Icons.vpn_key),
81          leading: const Icon(Icons.book),
82          title: Text(root.title,
83            style: TextStyle(
84              fontWeight: FontWeight.bold,
85              fontSize: 18,
86            ),),
87          subtitle: Text("movie"),
88          onTap: () {Navigator.push(
89            context,
90            MaterialPageRoute(builder: (context) => SecondRoute()),
91          );}
92
93      ),
94    );
95    //expansionリストの下から2番目にいる子供達
96    return Padding(
97      padding: const EdgeInsets.only(top:8.0,left:10.0),
98      child: ExpansionTile(
99        leading: const Icon(Icons.book),
100        key: PageStorageKey<Entry>(root),
101        title: Text(root.title,
102          style: TextStyle(
103            fontWeight: FontWeight.bold,
104            fontSize: 18,
105          ),),
106        subtitle: Text("unit"),
107        children: root.children.map(_buildTiles).toList(),
108      ),
109    );
110  }
111
112  @override
113  Widget build(BuildContext context) {
114    return _buildTiles(entry);
115  }
116}
117//2ページ目
118class SecondRoute extends StatefulWidget {
119  @override
120  _SecondRouteState createState() => _SecondRouteState();
121}
122以下、関係なさそうなので省略させていただきます。

恐らくですが、Widget build(BuildContext context)の扱い方を理解できていないのが原因だと考えております。ご回答、何卒よろしくお願いします

行動規範の内容に同意します

回答1件

ベストアンサー

MaterialPageRouteにはcontextが必要なので、以下のように_buildTilesの引数にcontextを追加して、渡してあげる必要があります。

  Widget build(BuildContext context) {
    return _buildTiles(context, entry);
  }

  Widget _buildTiles(BuildContext context, Entry root) {
    // 省略
  }

参考に動作確認した動くコードも載せておきます。

import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  @override
  _FirstRouteState createState() => _FirstRouteState();
}

class _FirstRouteState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text(
            'StudySummary',
            style: TextStyle(
              fontWeight: FontWeight.bold,
              fontStyle: FontStyle.italic,
              fontSize: 18,
            ),
          ),
        ),
        body: ListView.builder(
          itemBuilder: (BuildContext context, int index) {
            return Padding(
              padding: const EdgeInsets.only(top: 8.0, left: 9.0),
              child: EntryItem(data[index]),
            );
          },
          itemCount: data.length,
        ),
      ),
    );
  }
}

class Entry {
  Entry(this.title, [this.children = const <Entry>[]]);
  final String title;
  final List<Entry> children;
}

final List<Entry> data = <Entry>[
  Entry(
    '現代文',
  ),
  Entry(
    '数学',
  ),
  Entry(
    '英語',
  ),
  Entry(
    '化学',
  ),
  Entry(
    '物理',
  ),
  Entry(
    '社会',
  ),
  Entry(
    'その他',
  ),
];

// Displays one Entry. If the entry has children then it's displayed
// with an ExpansionTile.
class EntryItem extends StatelessWidget {
  const EntryItem(this.entry);

  final Entry entry;
//expansionリストの一番下にいる子供達

  Widget _buildTiles(BuildContext context, Entry root) {
    if (root.children.isEmpty)
      return Padding(
        padding: const EdgeInsets.only(left: 18.0),
        child: ListTile(

            //leading: const Icon(Icons.vpn_key),
            leading: const Icon(Icons.book),
            title: Text(
              root.title,
              style: TextStyle(
                fontWeight: FontWeight.bold,
                fontSize: 18,
              ),
            ),
            subtitle: Text("movie"),
            onTap: () {
              Navigator.push(
                context,
                MaterialPageRoute(builder: (context) => SecondRoute()),
              );
            }),
      );
    //expansionリストの下から2番目にいる子供達
    return Padding(
      padding: const EdgeInsets.only(top: 8.0, left: 10.0),
      child: ExpansionTile(
        leading: const Icon(Icons.book),
        key: PageStorageKey<Entry>(root),
        title: Text(
          root.title,
          style: TextStyle(
            fontWeight: FontWeight.bold,
            fontSize: 18,
          ),
        ),
        subtitle: Text("unit"),
        children:
            root.children.map((entry) => _buildTiles(context, entry)).toList(),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return _buildTiles(context, entry);
  }
}

//2ページ目
class SecondRoute extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Container(),
    );
  }
}

投稿2020/02/25 10:49