Map<String，dynamic> to Map<String，Map<String，String>> in Dart

Question

我正在尝试将Map<String,dynamic>转换为Map<String, Map<String, String>>

Map<String,dynamic> oldMap = querySnapshot.docs.first.data()["cach"];

Map<String, Map<String, String>> newMap = oldMap.map((a, b) => MapEntry(a, b as Map<String, String>)); 

但我有个错误：

Unhandled Exception: type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'Map<String, String>' in type cast

Answer 1

import 'dart:convert';

const rawData = '''
{"a": {"b": "c"}, "d":{"e": "f"}}
''';

Map<String, String> convert(Map<String, dynamic> data) {
  return Map<String,String>.fromEntries(data.entries.map<MapEntry<String,String>>((me) => MapEntry(me.key, me.value)));
}

void main(List<String> args) {
  var oldMap = jsonDecode(rawData) as Map<String, dynamic>;
  var newMap = Map.fromEntries(oldMap.entries.map((me) => MapEntry(me.key, convert(me.value))));
 
  print(newMap.runtimeType);
}

结果：

_InternalLinkedHashMap<String, Map<String, String>>