Firebase Firestore 错误:未为“Object"类定义运算符“[]" [英] Firebase Firestore Error: The operator '[]' isn't defined for the class 'Object'

问题描述

我正在通过这个视频学习如何将 Flutter 应用程序连接到 Firebase

im learning how to connect flutter app to firebase from this video

https://youtu.be/ggYTQn4WVuw

对我来说一切都完全一样，但在 Android Studio 中出现了错误.

For me everything is exactly the same, but in Android Studio there is an error.

错误:未为类型Object"定义运算符[]".(undefined_operator at [firebase_test] libservicesdatabase.dart:24)

error: The operator '[]' isn't defined for the type 'Object'. (undefined_operator at [firebase_test] libservicesdatabase.dart:24)

错误代码:

List<Brew> _brewListFromSnapshot(QuerySnapshot snapshot) {
return snapshot.docs.map((doc) {
  return Brew(
    name: doc.data()['name'] ?? '',
    strength: doc.data()['strength'] ?? 0,
    sugars: doc.data()['sugars'] ?? '0',
  );
}).toList();}

酿造课:

class Brew {
  final String name;
  final String sugars;
  final int strength;

  Brew({ this.name, this.sugars, this.strength });
}

有人可以帮我解决这个问题吗?这是 Android Studio 的问题吗?

Can someone help me fix this? Is this a problem with Android Studio?

推荐答案

您正在使用最新的 Firestore 依赖项 2.0.0 版，该版本于 2021 年 5 月 4 日发布.有重大更改，请在此处阅读.

You are using the latest Firestore dependency, version 2.0.0, which was released May 4th, 2021 days ago. There are breaking changes, read about them here.

添加 withConverter"，来自文档:

"Add withConverter", From the documentation:

将 withConverter 函数添加到 CollectionReference、DocumentReference 和 Query (#6015).这种新方法允许以类型安全的方式与集合/文档交互:

Add withConverter function to CollectionReference, DocumentReference and Query (#6015). This new method allows interacting with collections/documents in a type-safe way:

final modelsRef = FirebaseFirestore
     .instance
     .collection('models')
     .withConverter<Model>(
       fromFirestore: (snapshot, _) => Model.fromJson(snapshot.data()!),
       toFirestore: (model, _) => model.toJson(),
     );

 Future<void> main() async {
   // Writes now take a Model as parameter instead of a Map
   await modelsRef.add(Model());
   final Model model = await modelsRef.doc('123').get().then((s) => s.data());
 }

或者，您可以简单地使用:

Or, you can use simply:

String name = snapshot.data.get('name');
//instead of 
String name = (snapshot.data.data() as Map<String,dynamic>)['name']

如果你想要整个地图:

Map<String,dynamic> data = snapshot.data.data() as Map<String,dynamic>);
String name = data['name'] ?? '';

这篇关于Firebase Firestore 错误:未为“Object"类定义运算符“[]"的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！