How do you use Data Snapshot to retrieve data across multiple child nodes?

Question

I want to retrieve eventName and eventSport values found in each userID node.

I am still new to Android Studio.

My firebase database is organized by:

fir-login-31***
 event
  userID(retrieved from firebase authentication)
    Unique EventID(randomly generated by me)
      eventID: "Unique EventID
      eventName: "Test1
      eventSport: "TestSport12

Because every time a different user uploads data into the database, the data is stored within their firebase UserID Node from Firebase Authentication. Is there a way for me to still retrieve data from each user-generated node while still letting users store their data by their own UserID? I use their userID to setup read-write rules in FirabaseDatabase.

Host_Activity.java:

package com.example.songkwongwee.myapplication;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Spinner;
import android.widget.Toast;

import com.google.firebase.auth.FirebaseAuth;
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.ValueEventListener;

import java.util.ArrayList;
import java.util.List;

public class HostActivity extends AppCompatActivity {

    EditText editTextName;
    Button buttonAdd;
    Spinner spinnerSports;

    DatabaseReference databaseEvent;
    FirebaseAuth mAuth;

    ListView listViewEvents;

    List<Event> eventList;

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

        databaseEvent = FirebaseDatabase.getInstance().getReference("event");

        mAuth = FirebaseAuth.getInstance();

        editTextName = findViewById(R.id.editTextName);
        buttonAdd = findViewById(R.id.buttonHostGame);
        spinnerSports = findViewById(R.id.spinnerSports);

        listViewEvents = findViewById(R.id.listViewEvents);

        eventList = new ArrayList<>();

        buttonAdd.setOnClickListener(new View.OnClickListener() {   //click button method for adding event
            @Override
            public void onClick(View v) {
                addEvent();
            }
        });

    }

    @Override
    protected void onStart() {
        super.onStart();

        databaseEvent.addValueEventListener(new ValueEventListener() { //executed every time we change anything in database
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {   //contains all data in snapshot data object

                eventList.clear(); //clear artist list

                for(DataSnapshot eventSnapshot: dataSnapshot.getChildren()){
                    Event event = eventSnapshot.getValue(Event.class);

                    eventList.add(event); //every time new data entered, this method executes,fetch all artist from database
                }

                EventList adapter = new EventList(HostActivity.this, eventList);
                listViewEvents.setAdapter(adapter);

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }


    private void addEvent(){   //method for user to create event
        String name = editTextName.getText().toString().trim();
        String sport = spinnerSports.getSelectedItem().toString();

        if(!TextUtils.isEmpty(name)){   //if name is not empty

            String uid = mAuth.getUid(); //call uid method to get user id

            String id = databaseEvent.push().getKey();  //call id method to get random string key

            Event event = new Event(id, name, sport); //call event method to

            databaseEvent.child(uid).child(id).setValue(event);  //method to store node in organise form (Event>UserID>Event.UKey>Details)

            Toast.makeText(this,"Event added",Toast.LENGTH_LONG).show();    //Show UI
        }
        else{   //if name is empty
            Toast.makeText(this,"You should enter a name", Toast.LENGTH_LONG).show();   //Show error UI
        }

    }
}

Event.java:

public class Event {

    String eventId;
    String eventName;
    String eventSport;

    public Event(String eventId, String eventName, String eventSport){
        this.eventId = eventId;
        this.eventName = eventName;
        this.eventSport = eventSport;

    }

    public String getEventId() {
        return eventId;
    }

    public String getEventName() {
        return eventName;
    }

    public String getEventSport() {
        return eventSport;
    }

Answer 1

To retrieve eventname and eventsport, try the following:

FirebaseUser user=FirebaseAuth.getInstance().getCurrentUser();
DatabaseReference reference = FirebaseDatabase.getInstance().getReference("event").child(user.getUid());;

reference.addListenerForSingleValueEvent(new ValueEventListener() {
 @Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot datas: dataSnapshot.getChildren()){
   String eventname=datas.child("eventName").getValue().toString();
   String eventsport=datas.child("eventSport").getValue().toString();
    }
 }
 @Override
public void onCancelled(DatabaseError databaseError) {
  }
 });

You have this database:

event
userID(retrieved from firebase authentication)
 Unique EventID(randomly generated by me)
    eventID: "Unique EventID
    eventName: "Test1
    eventSport: "TestSport12

each userid is unique for that user, and since you want the user to retrieve his data then you can use user.getUid() which will retrieve the userid and then iterate inside of it to get the eventname and eventsport.