Flutter安全地图功能插件safemap的使用

Safemap

Safely get value with Type from JSON map. Will return null value when value was wrong.

Feature

• ✅ 安全取值：可以从Map中连续使用[]操作符取值，任何错误取值都会返回null而不会报错。
• ✅ 安全的嵌套Map：你可以轻松取出深度嵌套Map中的数据，因为即使对Value为null的SafeMap使用[]操作符，也只会返回一个新的SafeMap(null)对象。
• ✅ 按类型取值：支持直接取出期望类型的数据，类型不正确就会返回null而不会报错。
• ✅ 类似Js的空值判断：通过调用isEmpty()方法，空数组，空字典，空字符串或0都会返回true，帮助你快速判断空值。

Getting Started

示例代码

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    // source map
    Map map = {
      'id': 3,
      'tag': 'student',
      'info': {
        'name': 'Jerry',
      },
      'class': [
        {
          "name": 'class 1',
          'tag': '',
        },
        {},
      ],
    };
    SafeMap safeMap = SafeMap(map);

    // 取值,错误的类型会返回SafeMap(null)
    assert(safeMap['id'].value == 3);
    assert(safeMap['id'].string == null);

    // 错误的下标也会返回SafeMap(null)
    assert(safeMap['tag'].value == 'student');
    assert(safeMap['tag12345'].value == null);

    // 连续取值,可以一直安全取值,只会返回SafeMap(null).
    assert(safeMap['info']['name'].value == 'Jerry');
    assert(safeMap['a']['b']['b']['b']['b']['b'].value == null);

    // 取出数组，也可以通过数组下标继续取值
    assert(safeMap['class'].list.length == 2);
    assert(safeMap['class'][0]['name'].value == 'class 1');

    // {},[],0,'',null 都会被判断为空
    assert(safeMap['class'][0]['tag'].isEmpty());
    assert(safeMap['class'][1].isEmpty());

    // 越界也会返回SafeMap(null)，判断isEmpty为true
    assert(safeMap['class'][2].isEmpty());

    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: '断言结束，运行正常'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final String title;

  const MyHomePage({Key key, this.title}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Text(title),
      ),
    );
  }
}

解释

1. 导入包：

   import 'package:safemap/safemap.dart';
   

2. 创建源Map：

   Map map = {
     'id': 3,
     'tag': 'student',
     'info': {
       'name': 'Jerry',
     },
     'class': [
       {
         "name": 'class 1',
         'tag': '',
       },
       {},
     ],
   };
   

3. 创建SafeMap对象：

   SafeMap safeMap = SafeMap(map);
   

4. 取值：

   • 安全取值，错误的类型会返回null：

     assert(safeMap['id'].value == 3);
     assert(safeMap['id'].string == null);
     

   • 错误的下标也会返回SafeMap(null)：

     assert(safeMap['tag'].value == 'student');
     assert(safeMap['tag12345'].value == null);
     

   • 连续取值，可以一直安全取值，只会返回SafeMap(null)：

     assert(safeMap['info']['name'].value == 'Jerry');
     assert(safeMap['a']['b']['b']['b']['b']['b'].value == null);
     

   • 取出数组，也可以通过数组下标继续取值：

     assert(safeMap['class'].list.length == 2);
     assert(safeMap['class'][0]['name'].value == 'class 1');
     

   • 空值判断：

     assert(safeMap['class'][0]['tag'].isEmpty());
     assert(safeMap['class'][1].isEmpty());
     

   • 越界也会返回SafeMap(null)，判断isEmpty为true：

     assert(safeMap['class'][2].isEmpty());
     

5. 构建Flutter应用：

   return MaterialApp(
     title: 'Flutter Demo',
     theme: ThemeData(
       primarySwatch: Colors.blue,
     ),
     home: MyHomePage(title: '断言结束，运行正常'),
   );
   

6. 显示结果：

   class MyHomePage extends StatelessWidget {
     final String title;
   
     const MyHomePage({Key key, this.title}) : super(key: key);
   
     @override
     Widget build(BuildContext context) {
       return Scaffold(
         body: Center(
           child: Text(title),
         ),
       );
     }
   }
   

通过以上示例，你可以看到如何在Flutter中使用safemap插件来安全地从Map中取值，避免因错误的键或类型而导致的异常。