android - 在 null 上调用了方法“文本”

Question

我正在编写一个笔记应用程序，我希望将数据从“新笔记”屏幕发送到所有其他笔记都存在的主屏幕。在运行时，当我按下保存笔记按钮时，我得到一个错误。

The following NoSuchMethodError was thrown while handling a gesture:
The method 'Text' was called on null.
Receiver: null
Tried calling: Text("yog")

这是我使用的主页代码（main.dart）

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';
import 'package:notes/newnote.dart';

void main() {
  runApp(MaterialApp(home: MyApp(), initialRoute: 'main.dart', routes: {
    '/home': (context) => MyApp(),
    '/newnote': (context) => NewNote(),
  }));
}

class dat {
  final String title;
  final String text;

  dat(this.title, this.text);
}


 int x = 0;

final datas = List<dat>.generate(
  x,
  (x) => dat(
    'Note $x',
    'A description of what needs to be done for Todo $x',
  ),
);

class MyApp extends StatefulWidget {
  final List<dat> dats;

  //requiring the list of todos
  MyApp({Key key, @required this.dats}) : super(key: key);

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

class _MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(
          "Note-It!",
          textAlign: TextAlign.center,
          style: TextStyle(color: Colors.white),
        ),
        backgroundColor: Colors.black,
      ),
      body: Column(         //
          children: <Widget>[
      Padding(padding: EdgeInsets.fromLTRB(19.0, 19.0, 19.0, 19.0),),
            Expanded(
              child: ListView.builder(
                  itemCount: datas.length,
                  itemBuilder: (context, index) {
                    return ListTile(
                        title: Text(datas[x].text),
                        onTap: () {
                          Navigator.push( context,MaterialPageRoute( builder: (context) =>
                          DetailScreen(notedata: datas[index])));
                        });
                  }),
            ),
            Align(
              alignment: Alignment.bottomRight,
              child: FloatingActionButton(
                  child: Icon(Icons.add),
                  backgroundColor: Colors.black,
                  onPressed: () {
                    Navigator.pushNamed(context, '/newnote');
                  }),
            ),
          ],
        ),
    );

  }
}

class DetailScreen extends StatelessWidget {
  // Declare a field that holds the data.
   dat notedata;

  // In the constructor, require a data.
  DetailScreen({Key key, @required this.notedata}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    notedata = ModalRoute.of(context).settings.arguments;
    // Use the data to create the UI.
    return Scaffold(
      appBar: AppBar(
        title: Text(notedata.title),
      ),
      body: Padding(
        padding: EdgeInsets.all(16.0),
        child: Text(notedata.text),
      ),
    );
  }
}

这是用户添加新注释的页面的代码：

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';
import 'package:notes/main.dart';

void main() {
  runApp(MaterialApp(home: NewNote()));
}
String title = '';
String text = '';
final fromController1 = TextEditingController();
final fromController2 = TextEditingController();
var instance;
class NewNote extends StatefulWidget {
  @override
  _NewNoteState createState() => _NewNoteState();
}

class _NewNoteState extends State<NewNote> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("New Note"),
        backgroundColor: Colors.black,
      ),
      body: SingleChildScrollView(
        child: Padding(
          padding: EdgeInsets.fromLTRB(19.0, 19.0, 19.0, 19.0),
          child: SingleChildScrollView(
            child: Column(children: <Widget>[
              TextField(
                controller: fromController1,
                decoration: InputDecoration(
                    border: OutlineInputBorder(), labelText: "Title"),
                style: TextStyle(fontSize: 28.0),
              ),
              Padding(padding: EdgeInsets.fromLTRB(19.0, 19.0, 19.0, 0.0)),
              TextField(
                controller: fromController2,
                decoration: InputDecoration(
                    border: OutlineInputBorder(), labelText: "Text"),
                style: TextStyle(fontSize: 20.0),
                maxLines: null,
              ),
              Padding(padding: EdgeInsets.fromLTRB(19.0, 19.0, 19.0, 0.0)),
              Align(
                alignment: Alignment.bottomCenter,
                child: FloatingActionButton.extended(
                  label: Text("Save Note"),
                  icon: Icon(Icons.save),
                  backgroundColor: Colors.black,
                  onPressed: () {
                    x++;
                    Navigator.pushNamed(context, '/home',
                    arguments: {
                      'title' : instance.Text(fromController1.text),
                      'text' : instance.Text(fromController2.text),
                    }
                    );
                  },
                ),
              ),
            ]),
          ),
        ),
      ),
    );
  }
}

标签： androidflutterdart

Answer 1

您已经通过构造函数传递数据，所以您不需要 notedata = ModalRoute.of(context).settings.arguments;

请参考您的代码如下：

class DetailScreen extends StatelessWidget {
  // Declare a field that holds the data.
   dat notedata;

  // In the constructor, require a data.
  DetailScreen({Key key, @required this.notedata}) : super(key: key);

  @override
  Widget build(BuildContext context) {

    // Use the data to create the UI.
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.notedata.title),
      ),
      body: Padding(
        padding: EdgeInsets.all(16.0),
        child: Text(widget.notedata.text),
      ),
    );
  }

如果没有，这应该可以，然后让我知道