[英]Unable to query data from Firebase
我正在嘗試從 Firebase 檢索數據。這是我的代碼片段
Future main() async {
WidgetsFlutterBinding.ensureInitialized();
await Firebase.initializeApp();
// DatabaseReference ref = FirebaseDatabase.instance.ref();
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
Widget build(BuildContext context) {
final docRef = FirebaseFirestore.instance.collection('data').doc("rules");
docRef.get().then(
(DocumentSnapshot doc) {
final data = doc.data() as Map<String, dynamic>;
return MyHomePage(title: 'ARNET Helper',
rules: data['ruleslist']);
},
onError: (e) => print("Error getting document: $e"),
);
return Spinner(text: "Unable to retrieve data");
}
}
我確實將 google-services.json 添加到 android/app 文件夾中。 但是對於上面的代碼片段,“then”塊中的行似乎沒有被擊中並且微調器(即 return Spinner(text: "Unable to retrieve data");)總是被返回。
我確實將這些行添加到 AndroidManifest.xml
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.INTERNET"/>
我試着調試它。 但是第 46 行的斷點從未被擊中。 相反,執行直接進入第 52 行。我錯過了什么?
我什至嘗試過按照一位評論者的建議使用 FutureBuilder。 我總是得到“出了點問題..”微調器
@override
Widget build(BuildContext context) {
CollectionReference data = FirebaseFirestore.instance.collection('data');
return FutureBuilder<DocumentSnapshot>(
future: data.doc('rules').get(),
builder:
(BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
if (snapshot.hasError) {
return Spinner(text: 'Something went wrong...');
}
if (snapshot.hasData && !snapshot.data!.exists) {
return Spinner(text: 'Document does not exist...');
}
if (snapshot.connectionState == ConnectionState.done) {
Map<String, dynamic> data = snapshot.data! as Map<String, dynamic>;
return MyHomePage(title: 'ARNET Helper', rules: data['ruleslist'].entries.toList() as List<dynamic>);
}
return Spinner(text: 'Loading...');
},
);
}
}
問題是get()
是一個異步操作,你不能在build
中異步返回小部件。
解決此問題的最簡單方法是使用FutureBuilder
:
class MyApp extends StatelessWidget {
const MyApp({super.key});
@override
return FutureBuilder<String>(
future: FirebaseFirestore.instance.collection('data').doc("rules").get(),
builder: (BuildContext context, AsyncSnapshot<DocumentSnapshot> asyncSnapshot) {
if (snapshot.hasData) {
final data = asyncSnapshot.data!.data() as Map<String, dynamic>;
return MyHomePage(title: 'ARNET Helper', rules: data['ruleslist']);
}
else if (snapshot.hasError) {
return Text("Error: ${snapshot.error}")
}
else {
return Text("Loading user data...")
}
}
)
}
您是否初始化了 Firebase 實例?
await Firebase.initializeApp()
不確定是什么問題,但下面的配置有效。
pubspec.yaml
firebase_core: ^1.24.0
cloud_firestore: ^3.5.0
FutureBuilder 查詢
@override
Widget build(BuildContext context) {
CollectionReference data = FirebaseFirestore.instance.collection('data');
return FutureBuilder<DocumentSnapshot>(
future: data.doc("rules").get(),
builder:
(BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
if (snapshot.hasError) {
return Spinner(text: 'Something went wrong...');
}
if (snapshot.hasData && !snapshot.data!.exists) {
return Spinner(text: 'Document does not exist...');
}
if (snapshot.connectionState == ConnectionState.done) {
final data = snapshot.data!.get('ruleslist') ;
return MyHomePage(title: 'ARNET Helper', rules: data);
}
return Spinner(text: 'Loading...');
},
);
}
}
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