App updates data in firebase real-time database but doesn't show anything in recyclerview

Question

I am trying to add data onto firbase realtime database and retrieve that data on a recyclerview.I am successfully able to do that but when i try to retrieve data from firebase its not happening even-though when i try to print my data on logacat window i am successfully able to do that.

MainActivity.java

    import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.google.firebase.database.ChildEventListener;
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.shivam.fireapp.model.User;

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

public class MainActivity extends AppCompatActivity {
    private  Button button;
    private  Button button2;
    EditText editText;
    EditText editText2;
    String TAG ="MyTag";
    private ChildEventListener mchildeventlistener;
    private RecyclerView mRecyclerView;
    private mModelAdapter modelAdapter;
    private List<User> mDataList;

    DatabaseReference mRootRef= FirebaseDatabase.getInstance().getReference();
    DatabaseReference mRefMain =mRootRef.child("Users");
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button) findViewById(R.id.Senddata);
        button2 = (Button) findViewById((R.id.GetData));
        editText = (EditText) findViewById(R.id.Firstname);
        editText2 = (EditText) findViewById(R.id.Agee);
        mDataList = new ArrayList<>();

        mRecyclerView= findViewById(R.id.recyclerView);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        modelAdapter = new mModelAdapter(this,mDataList);
        mRecyclerView.setAdapter(modelAdapter);
        mchildeventlistener = new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
                User user = dataSnapshot.getValue(User.class);
                mDataList.add(user);
                modelAdapter.notifyDataSetChanged();

                Log.d(TAG,"OnChildAdded : Name    "+ user.getFirst_name());
                Log.d(TAG,"OnChildAdded : ageeee    "+ user.getAgeeee());



            }

            @Override
            public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {

            }

            @Override
            public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {

            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        };

        mRefMain.addChildEventListener(mchildeventlistener);





    }
    @Override
    protected void onStart(){
        super.onStart();
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                String Name = editText.getText().toString();
                String Age = editText2.getText().toString();

                User user = new User(Name,Age);

                String key = mRefMain.push().getKey();
                mRefMain.child(key).setValue(user);

                Toast.makeText(MainActivity.this,"Done",Toast.LENGTH_SHORT).show();
            }
        });







        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {



            }});



    }
    @Override
    protected void onDestroy(){
        super.onDestroy();
        mRefMain.removeEventListener(mchildeventlistener);
    }


}

activity_main.xml

    <?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">


    <Button
        android:id="@+id/Senddata"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="32dp"
        android:text="Send Data"
        app:layout_constraintBottom_toBottomOf="@+id/GetData"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="@+id/GetData" />

    <EditText
        android:id="@+id/Firstname"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="32dp"
        android:layout_marginTop="41dp"
        android:layout_marginEnd="39dp"
        android:ems="10"
        android:hint="Enter Name"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toStartOf="@+id/Agee"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/GetData"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="160dp"
        android:layout_marginEnd="40dp"
        android:text="Get Data"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/Agee"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginTop="41dp"
        android:layout_marginEnd="40dp"
        android:ems="10"
        android:hint="Entre a Age"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toEndOf="@+id/Firstname"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="345dp"
        android:layout_marginTop="55dp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/Senddata" />
</androidx.constraintlayout.widget.ConstraintLayout>

mModelAdapter.java

    import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.shivam.fireapp.model.User;

import java.util.List;

public class mModelAdapter extends RecyclerView.Adapter<mModelAdapter.MyViewHolder> {
    private Context context;
    private List<User> mDataList;

    public mModelAdapter(Context context, List<User> mDataList) {
        this.context = context;
        this.mDataList = mDataList;
    }

    @NonNull
    @Override
    public MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View rootView= LayoutInflater.from(context).inflate(R.layout.recycler_view_item,parent,false);

        return new MyViewHolder(rootView);
    }

    @Override
    public void onBindViewHolder(@NonNull MyViewHolder holder, int position) {
        User user = mDataList.get(position);
        holder.textView.setText(user.getFirst_name()+"  |  "+user.getAgeeee());

    }

    @Override
    public int getItemCount() {
        return mDataList.size();
    }

    public class MyViewHolder extends RecyclerView.ViewHolder{
        TextView textView;

        public MyViewHolder(@NonNull View itemView) {
            super(itemView);
            textView = itemView.findViewWithTag(R.id.textView);
        }
    }
}

User.java

    public class User {

    String first_name, ageeee;

    public User(String first_name, String ageeee) {
        this.first_name = first_name;
        this.ageeee = ageeee;
    }

    public User() {
    }

    public String getFirst_name() {
        return first_name;
    }

    public void setFirst_name(String first_name) {
        this.first_name = first_name;
    }

    public String getAgeeee() {
        return ageeee;
    }

    public void setAgeeee(String ageeee) {
        this.ageeee = ageeee;
    }
}

recycler_view_item.xml

    <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:text="TextView"
        android:textSize="24sp"
        android:gravity="center"/>
</LinearLayout>

score 1 · Accepted Answer · answered Mar 04 '20 at 06:15

1

I had the same problem. Its reason is that when firebase hasn't read data from realtime database yet, recyclerview has been made; and it hasn't have any data yet. For solving that you should make recyclerview when you are sure that firebase has read data. Then recyclerview will be made with correct data.

answered Mar 04 '20 at 06:15

MMG

3,226
5
16
43

This answer will help you more: https://stackoverflow.com/questions/43143134/ – MMG Mar 04 '20 at 06:17
1

App crashes after i setadapter – Shivam Mar 07 '20 at 18:49
This problem is for your recyclerview and it is another issue. Why did you uncheck my answer as correct answer? Ask another question about your recyclerview. – MMG Mar 07 '20 at 18:59
1

My problem arises when i settext into the textviews, when i don't pass any any text it simply shows me empty TextViews holder.textView.setText(user.getName()); holder.textView.setText(user.getAge()); when i simply omit these two statements i get epmty textviews in my recycler view but when i add these line i go into runtime error. – Shivam Mar 08 '20 at 09:00

score 1 · Answer 2 · answered Mar 04 '20 at 06:23

1

First i will recommend you don't pass list in adapter . Create setList method in adapter.

If you still passing list in adapter then TRY THIS

Replace this in line childadded method

  modelAdapter.notifyDataSetChanged();

With this two line

    modelAdapter = new mModelAdapter(this,mDataList); //this will recreate the adapter with new data
    mRecyclerView.setAdapter(modelAdapter); //Again set adapter to recyclerview

answered Mar 04 '20 at 06:23

Rahul sharma

1,492
12
26

I think problem is not with when i am setting adapter because when i don't set any values inside the adapter onBindViewholder method it just shows me empty textview in place of my data on fire base. – Shivam Mar 08 '20 at 13:34
@ShivamSehrawat `notifyDataSetChanged` works when your `mDataList` updated but you are not updating list. This is the problem . – Rahul sharma Mar 09 '20 at 08:18

score 1 · Answer 3 · answered Mar 04 '20 at 06:25

1

java inner class dos't access outer local declared variable.So you need do

 public List<User> mDataList = new ArrayList<>();

OR

use interface

answered Mar 04 '20 at 06:25

ashok

431
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8

App updates data in firebase real-time database but doesn't show anything in recyclerview

3 Answers3

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