【flutter】flutter的provider调用是报错

Z时代
2024-01-10
分类：技术分享

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

【flutter】flutter的provider调用是报错