无法查询到Firebase的数据

Question

我正在尝试从 Firebase 检索数据。这是我的代码片段

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");
  }

}  

下面是对应的Firebase数据库截图

我确实将 google-services.json 添加到 android/app 文件夹中。 但是对于上面的代码片段，“then”块中的行似乎没有被击中并且微调器（即 return Spinner(text: "Unable to retrieve data");）总是被返回。

我确实将这些行添加到 AndroidManifest.xml

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.INTERNET"/>

我试着调试它。 但是第 46 行的断点从未被击中。 相反，执行直接进入第 52 行。我错过了什么？

我什至尝试过按照一位评论者的建议使用 FutureBuilder。 我总是得到“出了点问题..”微调器

  @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...');
      },
    );
  }
}

Answer 1

问题是get()是一个异步操作，你不能在build中异步返回小部件。

解决此问题的最简单方法是使用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...")
      }    
    }    
  )
}  

Answer 2

您是否初始化了 Firebase 实例？

await Firebase.initializeApp()

Answer 3

不确定是什么问题，但下面的配置有效。

pubspec.yaml

  firebase_core: ^1.24.0
  cloud_firestore: ^3.5.0

FutureBuilder 查询

@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...');
      },
    );
  }
}