将Map转换为json字符串

Question

我是新来的dart，试图将Map转换为json字符串sqflite,json.encoder和jsonEncode不起作用。我试图使用json_serializable，但不能运行build_runner，做了一堆操作与元和分析器。

转换变量时出现的问题，这应该看起来像:

"variants": {
"iphone 6": {"1": "8", "2": "6"},
"xiaomi mi6": {"1": "8", "3": "5"},
"samsung A6": {"1": "8"}
}

它的样子:

variants: {
iphone 6: {1: 8, 2: 6},
xiaomi mi6: {1: 8, 3: 5},
samsung A6: {1: 8}
}

SQL函数:

Future<void> addToCart(List<List<TextEditingController>> controllers, Item item) async {
Map<String, Map<int, String>> resultMap = Map();
var list = item.variants.values.toList();
var models = item.variants.keys.toList();
for (int i = 0; list.length > i; i ++) {
var variantsName = list.elementAt(i).toList();
var modelsName = models.elementAt(i);
Map<int, String> values = Map();
for (int ind = 0; variantsName.length > ind; ind ++) {
String reasultC = controllers[i].elementAt(ind).text;
if (reasultC.isNotEmpty && int.parse(reasultC) > 0) {
values[ind + 1] = reasultC;
}
}
if (!resultMap.containsKey(modelsName) && values.isNotEmpty) {
resultMap[modelsName] = values;
}
}
db = await openDatabase("$_dbName.db");
db.execute('''
CREATE TABLE IF NOT EXISTS $_dbName(
id INTEGER PRIMARY KEY,
idItem TEXT,
title TEXT,
variants TEXT,
images TEXT)
''');
var end = Cart(idItem: item.id, title: item.title, variants: resultMap, images: item.images).toJson();
print(end);

await db.insert(_dbName, end);
await db.close();
}

class Cart {
String idItem;
String title;
Map<String, dynamic> variants;
List<String> images;
Cart({this.idItem, this.title, this.variants, this.images});
Map<String, dynamic> toJson() =>
<String, dynamic>{
'idItem': this.idItem,
'title': this.title,
'variants': jsonEncode(this.variants), <= NoSuchMethodError: Class '_InternalLinkedHashMap<int, String>' has no instance method 'toJson'. Receiver: _LinkedHashMap len:1 T
'images': json.encode(this.images)
};
}

谢谢。

Answer 1

使用json.encode:

可以正常工作

import 'dart:convert';
void main() {
try {
var obj = {
"variants": {
"iphone 6": {"1": "8", "2": "6"},
"xiaomi mi6": {"1": "8", "3": "5"},
"samsung A6": {"1": "8"}
}
};
String str = json.encode(obj);
print(str);
} catch(e) {
print(e);
}
}

DartPad联系

Answer 2

我发现了一个错误，这是一个非常幼稚的错误，将地图类型从Map <String, Map <int, String>更改为Map <String, Map <String, String >>

Map<String, Map<String, String>> resultMap = Map();
var list = item.variants.values.toList();
var models = item.variants.keys.toList();
for (int i = 0; list.length > i; i ++) {
var variantsName = list.elementAt(i).toList();
var modelsName = models.elementAt(i);
Map<String, String> values = Map();
for (int ind = 0; variantsName.length > ind; ind ++) {
String reasultC = controllers[i].elementAt(ind).text;
if (reasultC.isNotEmpty && int.parse(reasultC) > 0) {
values["${ind + 1}"] = reasultC;
}
}
if (!resultMap.containsKey(modelsName) && values.isNotEmpty) {
resultMap[modelsName] = values;
}
}

Answer 3

你可以简单地使用这个函数

String MapToJson(List<Map<String, dynamic>> map) {
String res = "[";
for (var s in map) {
res += "{";
for (String k in s.keys) {
res += '"';
res += k;
res += '":"';
res += s[k].toString();
res += '",';
}
res = res.substring(0, res.length - 1);
res += "},";
res = res.substring(0, res.length - 1);
}
res += "]";
return res;
}