Flutter状态管理之state-management

StatelessWidget

class StateManagementDemo extends StatelessWidget {
  int count = 0;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('StateManagementDemo'),
        elevation: 0.0,
      ),
      floatingActionButton: FloatingActionButton(
        child: Icon(Icons.add),
        onPressed: () {
          count++;
          print(count);//打印每次按一次会加1
        },
      ),
      body: Center(
        child: Chip(
          label: Text('$count'),//始终显示0
        ),
      ),
    );
  }
}

state传递InheritedWidget

import 'package:flutter/material.dart';

class StateManagementDemo extends StatefulWidget {
  @override
  _StateManagementDemoState createState() => _StateManagementDemoState();
}

class _StateManagementDemoState extends State<StateManagementDemo> {
  int count = 0;
  void _increaseCount() {
    setState(() {
      count++;
    });

    print(count);
  }

  @override
  Widget build(BuildContext context) {
    return CounterProvider(
      count: count,
      increaseCount: _increaseCount,
      child: Scaffold(
        appBar: AppBar(
          title: Text('StateManagementDemo'),
          elevation: 0.0,
        ),
        floatingActionButton: FloatingActionButton(
          child: Icon(Icons.add),
          onPressed: _increaseCount,
        ),
        body: StateWrapper(),
      ),
    );
  }
}

//从父辈继承state,本身不管理state
class StateWrapper extends StatelessWidget {
  
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return Counter();
  }
}

//从父辈继承state,本身不管理state
class Counter extends StatelessWidget {
 

  @override
  Widget build(BuildContext context) {
    final int count = CounterProvider.of(context).count;
    final VoidCallback _increaseCount =  CounterProvider.of(context).increaseCount;
    // TODO: implement build
    return Center(
      child: ActionChip(
        label: Text('$count'),
        onPressed: _increaseCount,
      ),
    );
  }
}

class CounterProvider extends InheritedWidget {
  final int count;
  final VoidCallback increaseCount;
  final Widget child;
  CounterProvider({this.count, this.increaseCount, this.child})
      : super(child: child);

  static CounterProvider of(BuildContext context) =>
      context.inheritFromWidgetOfExactType(CounterProvider);

  @override
  bool updateShouldNotify(InheritedWidget oldWidget) {
    // TODO: implement updateShouldNotify
    return true;
  }
}