Flutter JSON解析插件json_native的使用

Flutter JSON解析插件json_native的使用

如果您在Dart中处理JSON数据时遇到困难，并且json_serializable并不总是最佳选择，尤其是当JSON结构不明确或动态变化，或者您只需要提取少数几个值时，那么json_native插件可能会对您有所帮助。json_native插件旨在简化JSON解析过程，使代码更具可读性和可靠性。

概述

• 当JSON结构不明确或动态变化时。
• 当您只需要提取少数几个值，而创建一个完整的数据模型显得过于复杂时。
• 当您处理json_serializable无法处理的复杂类型，例如联合类型时。

在这种情况下，您可能会退回到原始的jsonDecode方法，但这种方法也带来了一系列挑战。

使用jsonDecode的问题

考虑以下JSON字符串：

{
  "int": 1,
  "string": "string",
  "double": 1.1,
  "bool": true,
  "intList": [1, 2, 3],
  "stringList": ["a", "b", "c"],
  "mixedList": ["a", 1, false],
  "obj": { "key": "value" },
  "foo": { "bar": { "baz": true, "string": "string" } },
  "mixed": [{ "object": { "key": "value" } }]
}

通常，您会使用以下代码来解析这个JSON字符串：

final root = jsonDecode(jsonString) as Map<String, dynamic>;

final intValue = root['int'] as int;
final strValue = root['string'] as String?;
final doubleValue = root['double'] as double;
final intList = (root['intList'] as List).cast<int>();
final stringList = (root['stringList'] as List).cast<String>();
final mixedList = root['mixedList'] as List;
final obj = root['obj'] as Map<String, dynamic>;
final baz = root['foo']['bar']['baz'] as bool;
final value = root['mixed'][0]['object']['key'] as String;

虽然这种方法功能上是可行的，但它存在一些缺点：

• 代码可读性差。
• 容易出错。
• 处理可选字段比较棘手。
• 调试起来可能比较困难。

使用json_native的解决方案

json_native插件旨在通过更易读且不易出错的代码来简化这一过程。

以下是具体实现步骤：

import 'package:json_native/json_native.dart';

final JsonObject root = jsonDecodeCast(jsonString);
// Yes, JsonObject isn't a new type but an type alias!
print(root.runtimeType == Map<String, dynamic>);

// get would cast the type for you
final intValue = root.get<int>('int');

// Yes, nullable type is also supported
final strValue = root.get<String?>('string');

// Type inference would figure out the generic param
final double doubleValue = root.get('double');

// Get a strong typed list
final intList = root.getList<int>('intList');

// Again, type inference would save the generic parameter.
final List<String> stringList = root.getList('stringList');

// If generic parameter is not given, it falls back to dynamic, which can be omitted.
final mixedList = root.getList('mixedList');

// getObj returns JsonObject.
final obj = root.getObj('obj');

// You can nested a series of get into a dig.
final baz = root.dig<bool>(['foo', 'bar', 'baz']);

// dig also support mixed of list and object
final value = root.dig<String>(['mixed', 0, 'object', 'key']);

特点

• 类型转换自动处理。
• 支持可空类型。
• 类型推断消除了显式泛型参数的需求。
• 提供强类型的列表。
• 允许通过dig进行嵌套对象和列表遍历。

完整示例代码

以下是一个完整的示例代码，展示了如何使用json_native插件解析JSON数据。

// ignore_for_file: unused_local_variable, avoid_dynamic_calls, avoid_print

import 'package:json_native/json_native.dart';

const jsonString = """
{
  "int": 1,
  "string": "string",
  "double": 1.1,
  "bool": true,
  "intList": [1, 2, 3],
  "stringList": ["a", "b", "c"],
  "obj": { "key": "value" },
  "foo": { "bar": { "baz": true, "string": "string" } },
  "mixed": [{ "object": { "key": "value" } }]
}
""";

void main() {
  vanilla();
  withJsonNative();
}

void vanilla() {
  final root = jsonDecode(jsonString) as Map<String, dynamic>;

  final intValue = root['int'] as int;
  final strValue = root['string'] as String;
  final doubleValue = root['double'] as double;
  final intList = (root['intList'] as List).cast<int>();
  final stringList = (root['stringList'] as List).cast<String>();
  final obj = root['obj'] as Map<String, dynamic>;
  final baz = root['foo']['bar']['baz'] as bool;
  final value = root['mixed'][0]['object']['key'] as String;
}

void withJsonNative() {
  final JsonObject root = jsonDecodeCast(jsonString);

  // Yes, JsonObject isn't a new type but an type alias!
  print(root.runtimeType == Map<String, dynamic>);

  // get would cast the type for you
  final intValue = root.get<int>('int');

  // Yes, nullable type is also supported
  final strValue = root.get<String?>('string');

  // Type inference would figure out the generic param
  final double doubleValue = root.get('double');

  // Get a strong typed list
  final intList = root.getList<int>('intList');

  // Again, type inference would save the generic parameter.
  final List<String> stringList = root.getList('stringList');

  // If generic parameter is not given, it falls back to dynamic, which can be omitted.
  final mixedList = root.getList('mixedList');

  // getObj returns JsonObject.
  final obj = root.getObj('obj');

  // You can nested a series of get into a dig.
  final baz = root.dig<bool>(['foo', 'bar', 'baz']);

  // dig also support mixed of list and object
  final value = root.dig<String>(['mixed', 0, 'object', 'key']);
}