flutter的provider调用是报错

Question

问题描述

简单计数器例子，想用flutter的provider实现

class CartPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body:Center(
        child: Column(
         children: <Widget>[
           Number(),
           MyButton()
         ],
        ),
      )
    );
  }
}

class Number extends StatelessWidget {

  @override
  Widget build(BuildContext context) {



    return Container(
        margin: EdgeInsets.only(top:200),
        child: Provide<Counter>(
          builder: (context,child,counter){
            return Text(
              '${counter.value}',
              style: Theme.of(context).textTheme.display1,
            );
          },
        ),
    );
  }
}


class MyButton extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return Container(
        child:RaisedButton(
          onPressed: (){
            Provide.value<Counter>(context).increment();
          },
          child: Text('递增'),
        )
    );
  }
}


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

class Counter with ChangeNotifier {
  int value =0 ;

  increment(){
    value++;
    notifyListeners();
  }
}

// main

void main(){
  var counter =Counter();
  var providers  =Providers();
  providers
    ..provide(Provider<Counter>.value(counter));
  runApp(ProviderNode(child:MyApp(),providers:providers));
}

问题出现的环境背景及自己尝试过哪些方法

但是会报错

 / (This is taking an unexpectedly long time
.)I/flutter (26528): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞════════════════════════════════════════════════════
═══════
I/flutter (26528): The following NoSuchMethodError was thrown building Provide<Counter>(dirty):
I/flutter (26528): The method 'getValue' was called on null.
I/flutter (26528): Receiver: null

你期待的结果是什么？实际看到的错误信息又是什么？

Answer 1

用大R刷新一遍就出来了，改变runApp节点什么的，需要强制刷新，改UI就不用，希望帮到你， 我刚刚也遇到这个问题