将项目添加到Dart / Flutter中嵌套地图内的列表中

用户名

致电时addItemToCart({"key": "val"})，我很难将项目添加到Dart / Flutter中嵌套地图内的列表中。var list = cart['items']给我一个空值，但我cart已经初始化了类成员。

它到底有什么问题？

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

class PData extends ChangeNotifier {
  dynamic cart = {"items": []};

  int itemCount = 0;
  String uid;
  String phoneNumber;

  void addItemToCart(val){
    var list = cart['items'];
    print("list ");
    print (list);

    list.add(val);
    notifyListeners();
  }

}

给出以下错误：

I/flutter ( 5763): list 
I/flutter ( 5763): null

════════ Exception caught by gesture ═══════════════════════════════════════════════════════════════
The following NoSuchMethodError was thrown while handling a gesture:
The method 'add' was called on null.
Receiver: null

尝试调用：add（_LinkedHashMap len：6）

苏吉

您需要添加.toList（）进行初始化。请参阅下面的示例代码片段：

var list = cart['items'];
var realList = list.toList();
print("list ");
print (list);

realList.add("soap");
print(realList);  // This prints [soap]
realList.add("Pen");
print(realList); // This prints [soap, pen]

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