Flutter可监听集合插件listenable_collections的使用

listenable_collections 是一个Dart集合库，它提供了一些特殊的集合类，这些集合类在数据发生变化时会像 ValueNotifier 一样通知监听器。目前实现了 ListNotifier，未来计划实现 MapNotifier 和 SetNotifier。

主要功能

• ListNotifier: 可监听的列表，当列表中的数据发生变化时，会通知所有监听器。
• MapNotifier 和 SetNotifier: 计划中的可监听映射和集合。

使用示例

示例代码

以下是一个使用 ListNotifier 的完整示例，展示了如何创建一个可监听的列表，并在列表变化时更新UI。

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:listenable_collections/listenable_collections.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'List Notifier Example'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  var _list = ListNotifier<String>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: SingleChildScrollView(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.start,
            children: <Widget>[
              actionsButtonMenu,
              ValueListenableBuilder<List<String>>(
                valueListenable: _list,
                builder: (context, value, child) => Column(
                  mainAxisSize: MainAxisSize.max,
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: _list.map<Widget>((value) => Text('List Item: $value')).toList(),
                ),
              )
            ],
          ),
        ),
      ),
    );
  }

  Row get actionsButtonMenu => Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          ElevatedButton(
            onPressed: _addItem,
            child: Icon(Icons.add),
          ),
          SizedBox(width: 16.0),
          ElevatedButton(
            onPressed: _removeItem,
            child: Icon(Icons.remove),
          ),
          SizedBox(width: 16.0),
          ElevatedButton(
            onPressed: _clearAllItems,
            child: Icon(Icons.delete),
          ),
        ],
      );

  void _addItem() {
    _list.add('${_list.length}');
  }

  void _removeItem() {
    if (_list.isNotEmpty) _list.removeLast();
  }

  void _clearAllItems() {
    if (_list.isNotEmpty) _list.clear();
  }
}

代码说明

1. 导入必要的包:

   import 'package:flutter/foundation.dart';
   import 'package:flutter/material.dart';
   import 'package:listenable_collections/listenable_collections.dart';
   

2. 创建 MyApp 类:

   void main() {
     runApp(MyApp());
   }
   
   class MyApp extends StatelessWidget {
     @override
     Widget build(BuildContext context) {
       return MaterialApp(
         theme: ThemeData(
           primarySwatch: Colors.blue,
           visualDensity: VisualDensity.adaptivePlatformDensity,
         ),
         home: MyHomePage(title: 'List Notifier Example'),
       );
     }
   }
   

3. 创建 MyHomePage 类:

   class MyHomePage extends StatefulWidget {
     MyHomePage({Key? key, required this.title}) : super(key: key);
   
     final String title;
   
     @override
     _MyHomePageState createState() => _MyHomePageState();
   }
   

4. 创建 _MyHomePageState 类:

   class _MyHomePageState extends State<MyHomePage> {
     var _list = ListNotifier<String>();
   
     @override
     Widget build(BuildContext context) {
       return Scaffold(
         appBar: AppBar(
           title: Text(widget.title),
         ),
         body: Padding(
           padding: const EdgeInsets.all(16.0),
           child: SingleChildScrollView(
             child: Column(
               crossAxisAlignment: CrossAxisAlignment.start,
               children: <Widget>[
                 actionsButtonMenu,
                 ValueListenableBuilder<List<String>>(
                   valueListenable: _list,
                   builder: (context, value, child) => Column(
                     mainAxisSize: MainAxisSize.max,
                     crossAxisAlignment: CrossAxisAlignment.start,
                     children: _list.map<Widget>((value) => Text('List Item: $value')).toList(),
                   ),
                 )
               ],
             ),
           ),
         ),
       );
     }
   
     Row get actionsButtonMenu => Row(
           mainAxisAlignment: MainAxisAlignment.center,
           children: [
             ElevatedButton(
               onPressed: _addItem,
               child: Icon(Icons.add),
             ),
             SizedBox(width: 16.0),
             ElevatedButton(
               onPressed: _removeItem,
               child: Icon(Icons.remove),
             ),
             SizedBox(width: 16.0),
             ElevatedButton(
               onPressed: _clearAllItems,
               child: Icon(Icons.delete),
             ),
           ],
         );
   
     void _addItem() {
       _list.add('${_list.length}');
     }
   
     void _removeItem() {
       if (_list.isNotEmpty) _list.removeLast();
     }
   
     void _clearAllItems() {
       if (_list.isNotEmpty) _list.clear();
     }
   }
   

关键点

• ListNotifier: 创建一个可监听的列表。
• ValueListenableBuilder: 用于构建依赖于 ValueListenable 的UI。当 ListNotifier 中的数据发生变化时，ValueListenableBuilder 会自动重新构建其子部件。
• 操作按钮: 提供了添加、删除和清空列表的功能。

通过这个示例，你可以看到如何使用 listenable_collections 插件来创建可监听的集合，并在数据变化时自动更新UI。希望这个示例对你有所帮助！