【Flutter】JSON String to List

紀錄一下JSON String的解析，包含將JSON String轉為Map或是JSON array String轉為List<Map>，或是直接將JSON String轉為List<Object>。

dart:convert

jsonDecode(jsonString) function

作用｜解析字串，回傳JSON object

範例｜

• String(JSON) → Map

import 'dart:convert';

const jsonString =
 '{"text": "foo", "value": 1, "status": false, "extra": null}';

Map<String, dynamic> data = jsonDecode(jsonString);
print(data['text']); // foo
print(data['value']); // 1
print(data['status']); // false
print(data['extra']); // null

 

• String(JSON array) → List of Map

import 'dart:convert';

const jsonArray = '''
  [{"text": "foo", "value": 1, "status": true},
   {"text": "bar", "value": 2, "status": false}]
''';
List<Object> _sidata = <StateMachine>[];

//String to List<Map>
final List<dynamic> dataList = jsonDecode(jsonArray);
print(dataList[0]);
print(dataList[1]);

//List<Map> to List<Object>
for (var item in dataList) {
  StateMachine pItem = StateMachine.fromJson(item);
  _sidata.add(pItem);
}
final item = dataList[0];
print(item['text']);
print(item['value']);
print(item['status']);

 

上面這個範例中，同時也要在StateMachine這個Class中新增一個「fromJson()」的function，例如：

factory StateMachine.fromJson(dynamic json) {
    return StateMachine(json['text'] as String, json['value'] as String, json['status'] as int);
  }

 

而上面也可以簡化為以下的寫法

import 'dart:convert';

const jsonArray = '''
  [{"text": "foo", "value": 1, "status": true},
   {"text": "bar", "value": 2, "status": false}]
''';

//String to List<Object>
var _sidata = jsonArray.map((x) => StateMachine.fromJson(x)).toList();