未为 class 'Object?' 定义运算符“[]”

Question

帮我解决下面的问题

import 'package:cloud_firestore/cloud_firestore.dart';

class UserModel{
  static const NUMBER = 'number';
  static const ID = 'id';

  String _number = '';
  String _id = '';

  String get number => _number;
  String get id => _id;

  UserModel.fromSnapshot(DocumentSnapshot snapshot){
    _number = snapshot.data()![NUMBER];
    _id = snapshot.data()![ID];
  }
}

有以下错误

lib/models/user_model.dart:16:30: Error: The operator '[]' isn't defined for the class 'Object?'.

'Object' is from 'dart:core'. Try correcting the operator to an existing operator, or defining a '[]' operator. _number = snapshot.data()[NUMBER]; ^ lib/models/user_model.dart:17:26: Error: The operator '[]' isn't defined for the class 'Object?'.

'Object' is from 'dart:core'. Try correcting the operator to an existing operator, or defining a '[]' operator. _id = snapshot.data()[ID];

Answer 1

在最新版本的 cloud firestore 中，DocumentSnapshot 是一个通用类型，因此您需要将类型参数与其一起传递。示例 -

import 'package:cloud_firestore/cloud_firestore.dart';

class UserModel{
  static const NUMBER = 'number';
  static const ID = 'id';

  String _number = '';
  String _id = '';

  String get number => _number;
  String get id => _id;

  UserModel.fromSnapshot(DocumentSnapshot<Map<String,dynamic>> snapshot){
    _number = snapshot.data()![NUMBER];
    _id = snapshot.data()![ID];
  }
}

未为 class 'Object?' 定义运算符“[]”

The operator '[]' isn't defined for the class 'Object?'

flutter

object

dart

snapshot