如何在Flutter中从Cloud Firestore加载数组和对象 [英] How do you load array and object from Cloud Firestore in Flutter
问题描述
我有一个包含几个嵌入式数组以及几个对象的类.我正在使用Flutter，无法弄清楚如何读写Cloud Firestore.
I have a class that has several embedded arrays as well as a couple of objects. I'm using Flutter and can't figure out how to read/write to Cloud Firestore.
我可以读写默认类型的数据成员，例如String和Int.这是我试图用来从DocumentSnapshot实例化对象的构造函数:
I can read/write data members that are default types like String and Int. Here is the constructor I'm trying to use to instantiate an object from a DocumentSnapshot:
class GameReview {
String name;
int howPopular;
List<String> reviewers;
}
class ItemCount {
int itemType;
int count;
ItemCount.fromMap(Map<dynamic, dynamic> data)
: itemType = data['itemType'],
count = data['count'];
}
class GameRecord {
// Header members
String documentID;
String name;
int creationTimestamp;
List<int> ratings = new List<int>();
List<String> players = new List<String>();
GameReview gameReview;
List<ItemCount> itemCounts = new List<ItemCount>();
GameRecord.fromSnapshot(DocumentSnapshot snapshot)
: documentID = snapshot.documentID,
name = snapshot['name'],
creationTimestamp = snapshot['creationTimestamp'],
ratings = snapshot['ratings'], // ERROR on run
players = snapshot['players'], // ERROR on run
gameReview = snapshot['gameReview']; // ERROR on run
itemCount = ????
}
它起作用，直到我添加最后3个成员(评分，玩家和gameReview).这应该很明显，但无论如何，它使我难以理解.
It works until I add the last 3 members (ratings, players and gameReview). This should be obvious but none the less, it eludes me.
帮助！
更新: 这是Cloud Firestore中存储的文档的示例.这存储在单个文档中.换句话说，我没有为嵌入式对象使用子集合.为了清楚起见，我将其放入JSON格式.我希望这会有所帮助.
UPDATE: Here is a sample of the document stored in Cloud Firestore. This is stored in a single document. In other words, I'm not using sub-collections for the embedded objects. I put it into a JSON format for clarity. I hope this helps.
{
"documentID": "asd8didjeurkff3",
"name": "My Game Record",
"creationTimestamp": 1235434,
"ratings": [
4,
2012,
4
],
"players": [
"Fred",
"Sue",
"John"
],
"gameReview": {
"name": "Review 1",
"howPopular": 5,
"reviewers": [
"Bob",
"Hanna",
"George"
]
},
"itemCounts": [
{
"itemType": 2,
"count": 3
},
{
"itemType": 1,
"count": 2
}
]
}
更新2: 我没有输入整个类的定义，因为我认为剩下的事情对我来说是显而易见的，但是事实并非如此.
UPDATE 2: I didn't put in the whole class definition because I thought it would be obvious to me how to do the rest but alas that was not the case.
我有一个要加载的对象列表.vbandrade的答案是"BANG"，但我不知道该如何创建对象列表. List.from(...)正在寻找迭代器，而不是创建的类.我敢肯定，创建一个新对象然后将其添加到列表中是一种变体，但我有些困惑. (请参见上面的类中的修改，具体是"itemCounts"成员.
I have a list of objects that I want to load.vbandrade's answer is BANG on but I can't quite figure out how I'm supposed to create the list of objects. List.from(...) is looking for an iterator, not a created class. I'm sure it's some variation of creating a new object and then adding it to a list but I'm a little confused. (see edits in class above, specifically, the "itemCounts" member.
推荐答案
从数组中加载列表，并让框架负责类型转换.
load the list from the array and let the framework take care of type casting.
一个对象就是一个地图，就像您在Json中编写的一样.我也使用命名构造函数. ((仍然学习并且不知道如何使用静态构造函数@ganapat提到))
an object is simply a map, like you wrote in your Json. I also use named constructor. ((still learning and dont know how to use the static constructor @ganapat mentioned))
这是工作代码.我保留了Firebase身份验证，并使用了StreamBuilder小部件.
here´s the working code. I kept firebase auth out and used the StreamBuilder widget.
import 'dart:async';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
import 'model/firebase_auth_service.dart';
void main() async {
runApp(new MyApp());
}
class MyApp extends StatelessWidget {
final firebaseAuth = new FirebaseAuthService();
MyApp() {
firebaseAuth.anonymousLogin();
}
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
body: Center(
child: FlatButton(
color: Colors.amber,
child: Column(
mainAxisSize: MainAxisSize.min,
children: <Widget>[
Text("get Game Record"),
StreamBuilder<GameRecord>(
stream: getGame(),
builder: (BuildContext c, AsyncSnapshot<GameRecord> data) {
if (data?.data == null) return Text("Error");
GameRecord r = data.data;
return Text("${r.creationTimestamp} + ${r.name}");
},
),
],
),
onPressed: () {
getGame();
},
))));
}
}
Stream<GameRecord> getGame() {
return Firestore.instance
.collection("games")
.document("zZJKQOuuoYVgsyhJJAgc")
.get()
.then((snapshot) {
try {
return GameRecord.fromSnapshot(snapshot);
} catch (e) {
print(e);
return null;
}
}).asStream();
}
class GameReview {
String name;
int howPopular;
List<String> reviewers;
GameReview.fromMap(Map<dynamic, dynamic> data)
: name = data["name"],
howPopular = data["howPopular"],
reviewers = List.from(data['reviewers']);
}
class GameRecord {
// Header members
String documentID;
String name;
int creationTimestamp;
List<int> ratings = new List<int>();
List<String> players = new List<String>();
GameReview gameReview;
GameRecord.fromSnapshot(DocumentSnapshot snapshot)
: documentID = snapshot.documentID,
name = snapshot['name'],
creationTimestamp = snapshot['creationTimestamp'],
ratings = List.from(snapshot['ratings']),
players = List.from(snapshot['players']),
gameReview = GameReview.fromMap(snapshot['gameReview']);
}
snapshot['itemCount']是一个对象数组.将数组中的每个项目映射到一个ItemCount对象，并以List的形式返回:
snapshot['itemCount'] is an array of objects. map each item in that array to an ItemCount object and return as a List:
itemCounts = snapshot['itemCount'].map<ItemCount>((item) {
return ItemCount.fromMap(item);
}).toList();
这篇关于如何在Flutter中从Cloud Firestore加载数组和对象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！
