Flutter部件内部状态管理小结之实现Vue的v-model功能

import 'package:flutter/material.dart';

class StateLessDemoWidget extends StatelessWidget {
 /// 如果定义非final修饰的成员变量，会提示
 /// This class (or a class which this class inherits from) is marked as '@immutable', but one or more of its instance fields are not final: StateLessDemoWidget.listInde
 /// int [listIndex];
 @override
 Widget build(BuildContext context) {
 return Container();
 }
}

import 'package:flutter/material.dart';

/// 创建一个继承[StatefulWidget]的widget类
/// 这个类的效果类似收藏，有个空心的爱心图标
/// 点击一下爱心填充红色，再点击一次就取消填充
class FavoriteWidget extends StatefulWidget {
 @override
 _FavoriteWidgetState createState() => _FavoriteWidgetState();
}

/// [State]类，FavoriteWidget的具体实现
/// 包含一个状态[_isFavorited]
class _FavoriteWidgetState extends State {
 bool _isFavorited = true;

 @override
 Widget build(BuildContext context) {
 return Row(
 mainAxisSize: MainAxisSize.min,
 children: [
 Container(
 padding: EdgeInsets.all(0),
 child: IconButton(
 /// [_isFavorited] 为 true 时使用图标 Icons.star 否则使用 Icons.star_border
 icon: (_isFavorited ? Icon(Icons.star) : Icon(Icons.star_border)),

 color: Colors.red[500],

 /// 当点击时，改变状态
 onPressed: _toggleFavorite,
 ),
 ),
 ],
 );
 }

 /// 改变[_isFavorited]的状态
 void _toggleFavorite() {
 setState(() {
 if (_isFavorited) {
 _isFavorited = false;
 } else {
 _isFavorited = true;
 }
 });
 }
}

import 'package:flutter/material.dart';

class TapboxA extends StatefulWidget {
 @override
 _TapboxAState createState() => _TapboxAState();
}
/// [TapboxA]拥有状态[_active]，通过[_handleTap]方法管理[_active]
class _TapboxAState extends State {
 bool _active = false;

 void _handleTap() {
 setState(() {
 _active = !_active;
 });
 }
 Widget build(BuildContext context) {
 return GestureDetector(
 onTap: _handleTap,
 child: Center(
 child: Text(
 _active ? 'Active' : 'Inactive',
 ),
 ),
 );
 }
}

import 'package:flutter/material.dart';

/// 父部件管理TapboxB的状态
///
/// 父部件[ParentWidget]定义了[_active]状态，并和[TapboxB]的[active]绑定
/// 当[TapboxB]被点击时，通过[onChanged]方法通知父部件，父部件修改[_active]的值
/// 也就间接修改了[TapboxB]的[active]
///
/// 如果了解过Vue的v-model原理的话比较好理解，其实这个和Vue的v-model一样的

//------------------------ ParentWidget --------------------------------

class ParentWidget extends StatefulWidget {
 @override
 _ParentWidgetState createState() => _ParentWidgetState();
}

class _ParentWidgetState extends State {
 bool _active = false;

 void _handleTapboxChanged(bool newValue) {
 setState(() {
 _active = newValue;
 });
 }

 @override
 Widget build(BuildContext context) {
 return Container(
 child: TapboxB(
 active: _active,
 onChanged: _handleTapboxChanged,
 ),
 );
 }
}

//------------------------- TapboxB ----------------------------------

// 注意[TapboxB]是无状态部件，所有成员变量使用 final 修饰
class TapboxB extends StatelessWidget {
 // 必须传递onChanged，用于通知父部件
 TapboxB({Key key, this.active: false, @required this.onChanged})
 : super(key: key);
 final bool active;
 final ValueChanged onChanged;

 void _handleTap() {
 // 通知父部件修改 active 的值
 onChanged(!active);
 }

 Widget build(BuildContext context) {
 return GestureDetector(
 // 被点击时
 onTap: _handleTap,
 child: Center(
 child: Text(
 // active 改变时修改文本的内容
 active ? 'Active' : 'Inactive',
 ),
 ),
 );
 }
}

import 'package:flutter/material.dart';
//---------------------------- ParentWidget ----------------------------

class ParentWidget extends StatefulWidget {
 @override
 _ParentWidgetState createState() => _ParentWidgetState();
}

class _ParentWidgetState extends State {
 bool _active = false;

 void _handleTapboxChanged(bool newValue) {
 setState(() {
 _active = newValue;
 });
 }

 @override
 Widget build(BuildContext context) {
 return Container(
 child: TapboxC(
 active: _active,
 onChanged: _handleTapboxChanged,
 ),
 );
 }
}

//----------------------------- TapboxC ------------------------------
class TapboxC extends StatefulWidget {
 TapboxC({Key key, this.active: false, @required this.onChanged})
 : super(key: key);

 final bool active;
 final ValueChanged onChanged;

 _TapboxCState createState() => _TapboxCState();
}

class _TapboxCState extends State {
 /// [TapboxC]管理内部的边框是否高亮，通过状态[_highlight]来修改
 bool _highlight = false;

 void _handleTapDown(TapDownDetails details) {
 setState(() {
 _highlight = true;
 });
 }

 void _handleTapUp(TapUpDetails details) {
 setState(() {
 _highlight = false;
 });
 }

 void _handleTapCancel() {
 setState(() {
 _highlight = false;
 });
 }

 void _handleTap() {
 // 通知父组件
 widget.onChanged(!widget.active);
 }

 Widget build(BuildContext context) {
 return GestureDetector(
 // onXXX都是事件处理
 onTapDown: _handleTapDown,
 onTapUp: _handleTapUp,
 onTap: _handleTap,
 onTapCancel: _handleTapCancel,
 child: Container(
 child: Center(
 child: Text(widget.active ? 'Active' : 'Inactive',
 style: TextStyle(fontSize: 32.0, color: Colors.white)),
 ),
 width: 200.0,
 height: 200.0,
 decoration: BoxDecoration(
 color: widget.active ? Colors.lightGreen[700] : Colors.grey[600],
 // 边框是否高亮显示
 border: _highlight
 ? Border.all(
  color: Colors.teal[700],
  width: 10.0,
 )
 : null,
 ),
 ),
 );
 }
}