提供者不更新文本小部件

Question

在 textField 小部件中输入一些文本后，我在更新 Level3 类中的文本小部件时遇到问题。 感谢您的帮助

在下面的代码中公开数据：

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      // home: TasksScreen(),
      home: ChangeNotifierProvider<Data>(
        create: (context) => Data(),
        child: Scaffold(
          appBar: AppBar(
            title: Container(
              child: MyText(),
            ),
          ),
          body: Level1(),
        ),
      ),
    );
  }
}

在下面的类中为模型数据创建数据类

class Data extends ChangeNotifier {
  String data = 'this data';

  void changeString(String newString) {
    data = newString;
    print(newString);//don't print anything after typing in textFild
    print(data);//don't print either
    notifyListeners();
  }
}

我想在下面的代码中使用 MyTextField 中的数据对象属性 但似乎没有触发Provider.of<Data>(context).changeString(newValue)

class MyTextField extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return TextField(
      onChanged: (newValue) {
        print(newValue);//print newValue correctly
        Provider.of<Data>(context).changeString(newValue);
      },
    );
  }
}

class Level3 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      child: Center(
        child: Text(
          //this part don't update as typing in textField
          Provider.of<Data>(context).data,
          //will return an instance of Provider
          //type found in the context that is sent as a parameter
        ),
      ),
    );
  }
}

Answer 1

你可以试试这个

(context.watch<Data>().data).toString();                        

Answer 2

您可以在下面复制粘贴运行完整代码
在onChanged，您可以使用listen: false
代码sn-p

return TextField(
      onChanged: (newValue) {
        print(newValue); //print newValue correctly
        Provider.of<Data>(context, listen: false).changeString(newValue);
      },
    );

工作演示

完整代码

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

class Data extends ChangeNotifier {
  String data = 'this data';

  void changeString(String newString) {
    data = newString;
    print(newString); //don't print anything after typing in textFild
    print(data); //don't print either
    notifyListeners();
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      // home: TasksScreen(),
      home: ChangeNotifierProvider<Data>(
        create: (context) => Data(),
        child: Scaffold(
          appBar: AppBar(
            title: Container(
              child: MyTextField(),
            ),
          ),
          body: Level3(),
        ),
      ),
    );
  }
}

class MyTextField extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return TextField(
      onChanged: (newValue) {
        print(newValue); //print newValue correctly
        Provider.of<Data>(context, listen: false).changeString(newValue);
      },
    );
  }
}

class Level3 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      child: Center(
        child: Text(
          //this part don't update as typing in textField
          Provider.of<Data>(context).data,
          //will return an instance of Provider
          //type found in the context that is sent as a parameter
        ),
      ),
    );
  }
}

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