Flutter 中的按钮 onclick 面临问题

Question

我不能 100% 确定如何最好地解释这个问题，但我会尽力而为。 我面临的问题是，每当我单击模拟器上的按钮到 go 到下一页时，我都会遇到很多错误，但应用程序本身可以正常运行而没有任何问题，只有当单击按钮时才会出现错误终点站。 错误如下所示：

E/dalvikvm( 1787): Could not find class 'android.view.inputmethod.CursorAnchorInfo$Builder', referenced from method io.flutter.plugin.editing.InputConnectionAdaptor.finishComposingText

W/dalvikvm( 1787): VFY: unable to resolve new-instance 411 (Landroid/view/inputmethod/CursorAnchorInfo$Builder;) in Lio/flutter/plugin/editing/InputConnectionAdaptor;

D/dalvikvm( 1787): VFY: replacing opcode 0x22 at 0x000e

D/dalvikvm( 1787): DexOpt: unable to opt direct call 0x0846 at 0x10 in Lio/flutter/plugin/editing/InputConnectionAdaptor;.finishComposingText

在主页上单击按钮时会弹出这些错误。 代码如下：

主页按钮代码：

onPressed: () { Navigator.push( context, MaterialPageRoute(builder: (context) => SharedPreference1())); },

该按钮通向另一个屏幕，在该屏幕中处理输入到 TextField 中的内容，该屏幕运行良好，但错误是在Home class 中预先单击该按钮时。

整个代码如下：

import 'package:shared_preferences/shared_preferences.dart';

TextEditingController _notesController1 = new TextEditingController();
TextEditingController _notesController2 = new TextEditingController();
List<String> data = [];

void main() => runApp(MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Home(),
    ));

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return (Scaffold(
      drawer: Drawer(
        child: ListView(
          children: <Widget>[
            ListTile(
              title: Text(
                'Glass',
                style: TextStyle(
                  fontSize: 15.0,
                  letterSpacing: 1.0,
                  color: Colors.black,
                  fontFamily: 'Montserrat',
                ),
              ),
            ),
            ListTile(
              title: Text('Trash'),
            ),
          ],
        ),
      ),
      backgroundColor: Colors.blueGrey[700],
      appBar: AppBar(
        title: Text(
          'Glass',
          style: TextStyle(
            fontSize: 20.0,
            letterSpacing: 1.0,
            color: Colors.white,
            fontFamily: 'Montserrat',
          ),
        ),
        centerTitle: true,
        backgroundColor: Colors.blueGrey[700],
      ),
      floatingActionButton: FloatingActionButton(
              elevation: 9.0,
        child: Icon(Icons.add),
        onPressed: () {
          Navigator.push(
              context, MaterialPageRoute(builder: (context) => SharedPreference1()));
        },
        backgroundColor: Colors.blueGrey[300],
      ),
      floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
    ));
  }
}

Future<bool> saveData(String nameKey, String value) async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    return await preferences.setString(nameKey, value);
  }

  Future<String> loadData(String nameKey) async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    return preferences.getString(nameKey);
  }

class Hero extends State<SharedPreference1> {
  Widget buildSaveButton(context) {
  return Container(
    color: Colors.blueGrey[700],
    margin: EdgeInsets.only(top:340.0),
    child: RaisedButton.icon(
      elevation: 9.0,
      icon: Icon(Icons.save),
      label: Text('Save'),
      color: Colors.white,
      onPressed: () async {
        await saveData("_key_name", _notesController2.text);
        await setData();
        print(data);
              },
            ),
          ); 
        }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        height: MediaQuery.of(context).size.height,
        width: MediaQuery.of(context).size.width,
        color: Colors.blueGrey[700],
        child: SafeArea(
          child: SingleChildScrollView(
            child: Column(
              children: <Widget>[
                buildHeading(context),
                buildNotesText(),
                buildSaveButton(context),
              ],
            ),
          ),
        ),
      ),
    );
  }
  @override
  void initState() {
    super.initState();
    setData();

  }

  setData() {
    loadData("_key_name").then((value) {
      setState(() {
        if(value==null){
          print("Value not available.");
        }
        else{
          data.add(value);
        }

      });
    });
  }

}

Widget buildHeading(context) {
  return Material(
    color: Colors.blueGrey[700],
    child: Padding(
      padding: const EdgeInsets.only(left: 20.0, top: 10.0),
      child: Row(
        children: <Widget>[
          Expanded(
            child: TextField(
              maxLines: 1,
              controller: _notesController1,
              decoration: InputDecoration(
                border: InputBorder.none,
                hintText: 'Note Title',
              ),
              style: TextStyle(fontSize: 20, color: Colors.white, fontFamily: 'Montserrat',),
            ),
          ),
          FlatButton(
            child: Icon(Icons.close, color: Colors.white, size: 27),
            onPressed: () {
              Navigator.of(context).pop();
            },
          )
        ],
      ),
    ),
  );
}

Widget buildNotesText() {
  return Material(
    color: Colors.blueGrey[700],
    child: Padding(
      padding: const EdgeInsets.all(20.0),
      child: TextField(
        maxLines: null,
        controller: _notesController2,
        decoration: InputDecoration(
          border: InputBorder.none,
          hintText: 'Create Note Here',
        ),
        cursorColor: Colors.white,
        autofocus: true,
        style: TextStyle(color: Colors.white,fontSize: 18,fontFamily: 'Montserrat'),
      ),
    ),
  );
}


class SharedPreference1 extends StatefulWidget {
  SharedPreference1() : super(); 
  @override
  Hero createState() => Hero();
}```

Answer 1

我不确定是什么导致了错误，但您的代码中有一些内容应该更改。 您应该始终在类中包含方法和变量，否则它们在全局 scope 中并且永远不会被释放。

每当您创建 controller 时，都需要正确创建和处置它（通常在您的initState和dispose方法中）。

我对您的代码进行了一些重构，以在您的类中包含所有全局范围的方法/变量。 看看这是否能解决您的问题。

import 'package:flutter/material.dart';
import 'package:shared_preferences/shared_preferences.dart';

void main() {
  runApp(
    MaterialApp(
      debugShowCheckedModeBanner: false,
      home: Home(),
    ),
  );
}

class Hero extends State<SharedPreference1> {
  TextEditingController _notesController1;
  TextEditingController _notesController2;
  List<String> data = [];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        height: MediaQuery.of(context).size.height,
        width: MediaQuery.of(context).size.width,
        color: Colors.blueGrey[700],
        child: SafeArea(
          child: SingleChildScrollView(
            child: Column(
              children: <Widget>[
                buildHeading(context),
                buildNotesText(),
                buildSaveButton(context),
              ],
            ),
          ),
        ),
      ),
    );
  }

  Widget buildHeading(context) {
    return Material(
      color: Colors.blueGrey[700],
      child: Padding(
        padding: const EdgeInsets.only(left: 20.0, top: 10.0),
        child: Row(
          children: <Widget>[
            Expanded(
              child: TextField(
                maxLines: 1,
                controller: _notesController1,
                decoration: InputDecoration(
                  border: InputBorder.none,
                  hintText: 'Note Title',
                ),
                style: TextStyle(
                  fontSize: 20,
                  color: Colors.white,
                  fontFamily: 'Montserrat',
                ),
              ),
            ),
            FlatButton(
              child: Icon(Icons.close, color: Colors.white, size: 27),
              onPressed: () {
                Navigator.of(context).pop();
              },
            )
          ],
        ),
      ),
    );
  }

  Widget buildNotesText() {
    return Material(
      color: Colors.blueGrey[700],
      child: Padding(
        padding: const EdgeInsets.all(20.0),
        child: TextField(
          maxLines: null,
          controller: _notesController2,
          decoration: InputDecoration(
            border: InputBorder.none,
            hintText: 'Create Note Here',
          ),
          cursorColor: Colors.white,
          autofocus: true,
          style: TextStyle(
              color: Colors.white, fontSize: 18, fontFamily: 'Montserrat'),
        ),
      ),
    );
  }

  Widget buildSaveButton(context) {
    return Container(
      color: Colors.blueGrey[700],
      margin: EdgeInsets.only(top: 340.0),
      child: RaisedButton.icon(
        elevation: 9.0,
        icon: Icon(Icons.save),
        label: Text('Save'),
        color: Colors.white,
        onPressed: () async {
          await saveData("_key_name", _notesController2.text);
          await setData();
          print(data);
        },
      ),
    );
  }

  setData() {
    loadData("_key_name").then((value) {
      setState(() {
        if (value == null) {
          print("Value not available.");
        } else {
          data.add(value);
        }
      });
    });
  }

  Future<bool> saveData(String nameKey, String value) async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    return await preferences.setString(nameKey, value);
  }

  Future<String> loadData(String nameKey) async {
    SharedPreferences preferences = await SharedPreferences.getInstance();
    return preferences.getString(nameKey);
  }
}

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return (Scaffold(
      drawer: Drawer(
        child: ListView(
          children: <Widget>[
            ListTile(
              title: Text(
                'Glass',
                style: TextStyle(
                  fontSize: 15.0,
                  letterSpacing: 1.0,
                  color: Colors.black,
                  fontFamily: 'Montserrat',
                ),
              ),
            ),
            ListTile(
              title: Text('Trash'),
            ),
          ],
        ),
      ),
      backgroundColor: Colors.blueGrey[700],
      appBar: AppBar(
        title: Text(
          'Glass',
          style: TextStyle(
            fontSize: 20.0,
            letterSpacing: 1.0,
            color: Colors.white,
            fontFamily: 'Montserrat',
          ),
        ),
        centerTitle: true,
        backgroundColor: Colors.blueGrey[700],
      ),
      floatingActionButton: FloatingActionButton(
        elevation: 9.0,
        child: Icon(Icons.add),
        onPressed: () {
          Navigator.push(context,
              MaterialPageRoute(builder: (context) => SharedPreference1()));
        },
        backgroundColor: Colors.blueGrey[300],
      ),
      floatingActionButtonLocation: FloatingActionButtonLocation.centerFloat,
    ));
  }
}

class SharedPreference1 extends StatefulWidget {
  SharedPreference1() : super();
  @override
  Hero createState() => Hero();
}