Flutter数据过滤插件where_not_null的使用

Flutter数据过滤插件where_not_null的使用

where_not_null 是一个用于 Iterable<T?> 的扩展方法，它将 Iterable<T?> 转换为 Iterable<T>。由于 Dart 类型系统的原因，这种转换变得有些复杂。

示例代码

以下是一个完整的示例代码，展示了如何在 Flutter 应用中使用 where_not_null 插件。

import 'package:flutter/material.dart';
import 'package:where_not_null/where_not_null.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('where_not_null 示例'),
        ),
        body: Center(
          child: ExampleWidget(),
        ),
      ),
    );
  }
}

class ExampleWidget extends StatefulWidget {
  @override
  _ExampleWidgetState createState() => _ExampleWidgetState();
}

class _ExampleWidgetState extends State<ExampleWidget> {
  List<int?> _list = [1, 2, null, 4, null];

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text(
          '原始列表: ${_list.join(", ")}',
          style: TextStyle(fontSize: 18),
        ),
        SizedBox(height: 20),
        ElevatedButton(
          onPressed: () {
            int sum = _list.whereNotNull().reduce((a, b) => a + b);
            setState(() {
              _list = [sum];
            });
          },
          child: Text('计算非空元素之和'),
        ),
        SizedBox(height: 20),
        Text(
          '计算结果: ${_list.join(", ")}',
          style: TextStyle(fontSize: 18),
        ),
      ],
    );
  }
}

解释

1. 导入必要的包：

   import 'package:flutter/material.dart';
   import 'package:where_not_null/where_not_null.dart';
   

2. 定义主应用类 MyApp：

   class MyApp extends StatelessWidget {
     @override
     Widget build(BuildContext context) {
       return MaterialApp(
         home: Scaffold(
           appBar: AppBar(
             title: Text('where_not_null 示例'),
           ),
           body: Center(
             child: ExampleWidget(),
           ),
         ),
       );
     }
   }
   

3. 定义示例组件 ExampleWidget：

   class ExampleWidget extends StatefulWidget {
     @override
     _ExampleWidgetState createState() => _ExampleWidgetState();
   }
   
   class _ExampleWidgetState extends State<ExampleWidget> {
     List<int?> _list = [1, 2, null, 4, null];
   
     @override
     Widget build(BuildContext context) {
       return Column(
         mainAxisAlignment: MainAxisAlignment.center,
         children: [
           Text(
             '原始列表: ${_list.join(", ")}',
             style: TextStyle(fontSize: 18),
           ),
           SizedBox(height: 20),
           ElevatedButton(
             onPressed: () {
               int sum = _list.whereNotNull().reduce((a, b) => a + b);
               setState(() {
                 _list = [sum];
               });
             },
             child: Text('计算非空元素之和'),
           ),
           SizedBox(height: 20),
           Text(
             '计算结果: ${_list.join(", ")}',
             style: TextStyle(fontSize: 18),
           ),
         ],
       );
     }
   }