firebase数据库访问未调用onChange方法

Question

import android.util.Log;

import androidx.annotation.NonNull;

import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.Query;
import com.google.firebase.database.ValueEventListener;

import java.util.ArrayList;

public class LockerDatabase implements ValueEventListener{
    private FirebaseDatabase database;
    private DatabaseReference reference;

    private User currUser;
    private ArrayList<Password> passwords;

    public int count;

    public LockerDatabase(String email, String name) {
        database = FirebaseDatabase.getInstance();
        reference = database.getReference();

        currUser = new User();
        passwords = new ArrayList<>();

        if (!exists(email))
            createUser(email, name);
        else
            loadPasswords();
    }

    private void loadPasswords() {
        //TODO: read from db all passwords
    }

    public String getEmail(){
        return currUser.getEmail();
    }

    private void createUser(String email, String name) {
        currUser.setEmail(email);
        currUser.setName(name);
        currUser.setHashId(Integer.toString(email.hashCode()));

        //TODO: add user to database
    }

    private boolean exists(String email) {
        Query existence = reference.child("users").child(Integer.toString(email.hashCode()));
        existence.addValueEventListener(this);

        if (currUser == null)
            return false;
        else
            return true;
    }

    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        currUser.setEmail((String)dataSnapshot.child("email").getValue());
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.w("CAN", "user_cancelled", databaseError.toException());
    }

 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.locker_layout);

    Intent intent = getIntent();
    userEmail = intent.getStringExtra("email");
    userName = intent.getStringExtra("name");

    db = new LockerDatabase(userEmail, userName);

    TextView t = findViewById(R.id.textView);
    t.setText(db.getEmail());

    //TODO: display db results
    //TODO: if the user is new, set an access key
}

Answer 1

不要使用Integer.ToString(email.hashcode())作为子级，或者使用push()方法生成随机密钥，或者使用userUID（如果使用firebase身份验证）。

如果使用push()，则首先存储密钥：

String key  = reference.child("users").push().getKey();

然后，当您要检索数据时，请执行以下操作：

Query existence = reference.child("users").child(key);
existence.addValueEventListener(this);