Question

我正在尝试检查已登录用户是否是Firebase数据库中JSON阵列的授权用户。如何从Firebase获取电子邮件字段的值。？

这是模型 User类：

public class User {

    ArrayList<User> email;

    public User() {}

    public ArrayList<User> getEmail() {
        return email;
    }

    public void setEmail(ArrayList<User> email) {
        this.email = email;
    }
}

为了从email获取userslist，我使用了这个逻辑。

usersListDatabaseReference.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        User userEmail = dataSnapshot.getValue(User.class);
                        ArrayList<String> userEmailFromDatabase = userEmail.getEmail();
                        Log.d(TAG, "User email from Database: "+userEmailFromDatabase);
                        Log.d(TAG, "Logged in User email: " + user.getEmail());
                    }

但是当我尝试从数据库中获取电子邮件时，我收到以下异常，我的应用程序崩溃了。

com.google.firebase.database.DatabaseException: Can't convert object of type java.util.ArrayList to type com.apvolution.amapp.model.User

如何获得'email from the userslist field ? How do I loop through the entire usersList`？

这是我的Firebase控制台中的数据库结构。

amapp-731b2addclose
   + messages
   + version
   - userslist
      - email
         |
         | -- 0: "abc@gmail.com"
         | -- 1: "xyz@gmail.com"
         | -- 2: "ghi@gmail.com"
         | -- 3: "mno@gmail.com"

LogCat详细信息：

05 - 13 21: 59: 37.418 16387 - 16387 / com.apvolution.bcm E / AndroidRuntime: FATAL EXCEPTION: main
Process: com.apvolution.bcm, PID: 16387
com.google.firebase.database.DatabaseException: Can 't convert object of type java.lang.String to type com.apvolution.amapp.model.User
at com.google.android.gms.internal.zzbtg.zze(Unknown Source)
at com.google.android.gms.internal.zzbtg.zzb(Unknown Source)
at com.google.android.gms.internal.zzbtg.zza(Unknown Source)
at com.google.android.gms.internal.zzbtg.zza(Unknown Source)
at com.google.android.gms.internal.zzbtg.zza(Unknown Source)
at com.google.android.gms.internal.zzbtg.zza(Unknown Source)
at com.google.firebase.database.DataSnapshot.getValue(Unknown Source)
at com.apvolution.bcm.MainActivity$3.onDataChange(MainActivity.java: 260)
at com.google.android.gms.internal.zzbpx.zza(Unknown Source)
at com.google.android.gms.internal.zzbqx.zzZT(Unknown Source)
at com.google.android.gms.internal.zzbra$1.run(Unknown Source)
at android.os.Handler.handleCallback(Handler.java: 751)
at android.os.Handler.dispatchMessage(Handler.java: 95)
at android.os.Looper.loop(Looper.java: 154)
at android.app.ActivityThread.main(ActivityThread.java: 6123)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java: 867)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java: 757)

Answer 1

您可以尝试将数据存储在ArrayList而不是Map中。更改Map<String, Object> map = new HashMap<>();中的类型，您的问题就会得到解决。

要从dataSnapshot对象中获取数据，请使用以下代码：

DatabaseReference yourRef = FirebaseDatabase.getInstance().getReference().child("userslist").child("email");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        String firstEmail = (String) dataSnapshot.child("0").getValue();
        String secondEmail = (String) dataSnapshot.child("1").getValue();
        String thirdEmail = (String) dataSnapshot.child("3").getValue();
        String fourthEmail = (String) dataSnapshot.child("4").getValue();
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
yourRef.addListenerForSingleValueEvent(eventListener);

希望它有所帮助。

Answer 2

似乎DataSnapshot的{{1}}要求您提交getValue(GenericTypeIndicator)而非List<YourCustomModel>，请参阅this link from Firebase docs。这意味着你应该这样做：

YourCustomModel

然后，从那里，单独检索每封电子邮件。您可能想要重新检查您的用户模型的执行方式，因为它可能不需要它自己的GenericTypeIndicator<List<User>> t = new GenericTypeIndicator<List<User>>() {}; List<User> userEmail = dataSnapshot.getValue(t);

无法从firebase数据库

2 个答案: