我正在尝试使用 Future
从 Firestore 数据库中获取单个字符串数据并在 FutureBuilder
中使用该数据后.但是得到null
快照数据中的值。提供了下面的完整代码。告诉我哪里出错了。
我可以打印 fetchPost()
中的数据功能。从 firestore 获取数据后,它进入 FutureBuilder
,
但快照数据为空- AsyncSnapshot<String>(ConnectionState.done, null, null)
import 'dart:async';
import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
Future <String>fetchPost() async {
final DocumentReference documentReference = Firestore.instance.document("myData/dummy");
documentReference.get().then((datasnapshot){
if(datasnapshot.exists){
print("get data" +datasnapshot.data['url']); ///this printing data //in console
return datasnapshot.data['url'];
}
}).catchError((e){
print("Error");
print(e);
});
}
void main() => runApp(MyApp(post: fetchPost()));
class MyApp extends StatelessWidget {
final Future<String> post;
MyApp({Key key, this.post}) : super(key: key);
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Fetch Data Example',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: Scaffold(
appBar: AppBar(
title: Text('Fetch Data Example'),
),
body: Center(
child: FutureBuilder<String>(
future: post,
builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
print ("snapshot has data");
print (snapshot); // this printing 'AsyncSnapshot<String>(ConnectionState.done, null, null)'
print (snapshot.data);// this printing null
if (snapshot.hasData) {
return Text(snapshot.data);
} else if (snapshot.hasError) {
return Text("${snapshot.error}");
}
// By default, show a loading spinner
return CircularProgressIndicator();
},
),
),
),
);
}
}
最佳答案
更改您的 FutureBuilder
使用以下代码,它应该适合您
FutureBuilder(
future: Firestore.instance.collection("myData").document("dummy").get(),
builder: (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.none:
return Text('Press button to start.');
case ConnectionState.active:
case ConnectionState.waiting:
return Text('Awaiting result...');
case ConnectionState.done:
if (snapshot.hasError)
return Text('Error: ${snapshot.error}');
return Text('Result: ${snapshot.data}');
// You can reach your snapshot.data['url'] in here
}
return null; // unreachable
},
);
关于firebase - Flter-FutureBuilder-未获取 AsyncSnapshot 数据,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/55321523/