I have made an app that retrieves data from a firebase real-time database and displays it in a RecyclerView.
MainActivity.java:
package com.example.myapplication;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.widget.Button;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
import android.widget.TextView;
import com.google.firebase.FirebaseApp;
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;
public class MainActivity extends AppCompatActivity {
RecyclerView recyclerview;
ArrayList<Dishes> list;
DatabaseReference reference;
Food_RecyclerViewAdapter adapter;
Button button;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerview = findViewById(R.id.recycler);
reference = FirebaseDatabase.getInstance().getReference("Dishes");
recyclerview.setHasFixedSize(true);
recyclerview.setLayoutManager(new LinearLayoutManager(this));
button = findViewById(R.id.button);
list = new ArrayList<>();
adapter = new Food_RecyclerViewAdapter(this, list);
recyclerview.setAdapter(adapter);
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot snapshot) {
for (DataSnapshot ds : snapshot.getChildren()){
//Add firebase data to Recyclerview adapter
Dishes dish = ds.getValue(Dishes.class);
list.add(dish);
}
adapter.notifyDataSetChanged();
}
@Override
//when the connection is cancelled call the Display() method
public void onCancelled(@NonNull DatabaseError error) {
Display();
}
});
}
private void Display() {
//Display the toast message "Error"
Toast.makeText(this, "Error", Toast.LENGTH_SHORT).show();
}
}
The Model class for the RecyclerView:
package com.example.myapplication;
class Dishes {
String name;
int price;
float rating;
public Dishes(String name, float rating, int price) {
this.name = name;
this.price = price;
this.rating = rating;
}
public String getName() {
return name;
}
public int getPrice() {
return price;
}
public float getRating() {
return rating;
}
}
The RecyclerView adapter:
package com.example.myapplication;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.RatingBar;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import java.util.ArrayList;
class Food_RecyclerViewAdapter extends RecyclerView.Adapter<Food_RecyclerViewAdapter.MyViewHolder> {
Context context;
ArrayList<Dishes> models;
public Food_RecyclerViewAdapter(Context context, ArrayList<Dishes> models){
this.context = context;
this.models = models;
}
@NonNull
@Override
public Food_RecyclerViewAdapter.MyViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
LayoutInflater inflater = LayoutInflater.from(context);
View view = inflater.inflate(R.layout.item, parent, false);
return new Food_RecyclerViewAdapter.MyViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull Food_RecyclerViewAdapter.MyViewHolder holder, int position) {
Dishes dish = models.get(position);
holder.name.setText(dish.getName());
holder.price.setText("Price" " $ " dish.getPrice());
holder.rating.setRating(dish.getRating());
}
@Override
public int getItemCount() {
return models.size();
}
public static class MyViewHolder extends RecyclerView.ViewHolder{
TextView name, price;
Button button;
RatingBar rating;
public MyViewHolder(@NonNull View ItemView) {
super(ItemView);
name = ItemView.findViewById(R.id.food_name);
price = ItemView.findViewById(R.id.pri);
button = ItemView.findViewById(R.id.btn);
rating = ItemView.findViewById(R.id.ratingBar);
}
}
}
Dependencies:
dependencies {
implementation 'androidx.appcompat:appcompat:1.3.0'
implementation 'com.google.android.material:material:1.4.0'
implementation 'androidx.constraintlayout:constraintlayout:2.0.4'
implementation 'com.google.firebase:firebase-database:20.0.3'
testImplementation 'junit:junit:4. '
androidTestImplementation 'androidx.test.ext:junit:1.1.3'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}
However when I run the app on my device "Samsung" the data does not load and the Oncancelled method is called when these rules are used:
{
"rules": {
".read": false,
".write": false
}
}
And when read and write are set to true the app just crashes:
{
"rules": {
".read": true,
".write": true
}
}
I am guessing that there is one thing I did wrong or am missing out, what is it? I am new to firebase so explaining as well as help would be appreciated, thankyou.
edit: Stack trace on logcat reads: 02-14 16:40:29.800 32134-32142/? W/SQLiteConnectionPool: A SQLiteConnection object for database ' data data com_android_vending databases resource_data_db' was leaked! Please fix your application to end transactions in progress properly and to close the database when it is no longer needed.
edit2: when the app crashes this error is given to me: 02-14 18:42:33.075 14095-14095/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main com.google.firebase.database.DatabaseException: Class com.example.myapplication.Dishes does not define a no-argument constructor. If you are using ProGuard, make sure these constructors are not stripped. at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:570) at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(CustomClassMapper.java:563) at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(CustomClassMapper.java:433) at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:232) at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:80) at com.google.firebase.database.DataSnapshot.getValue(DataSnapshot.java:203) at com.example.myapplication.MainActivity$1.onDataChange(MainActivity.java:54) at com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75) at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63) at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55) at android.os.Handler.handleCallback(Handler.java:615) at android.os.Handler.dispatchMessage(Handler.java:92) at android.os.Looper.loop(Looper.java:137) at android.app.ActivityThread.main(ActivityThread.java:4947) at java.lang.reflect.Method.invokeNative(Native Method) at java.lang.reflect.Method.invoke(Method.java:511) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805) at dalvik.system.NativeStart.main(Native Method)
edit 3: I have solved the problem after doing snachsms answer, adding another empty constructor in dishes:
public Dishes(){}
public Dishes(String name, float rating, int price) {
this.name = name;
this.price = price;
this.rating = rating;
}
Great thanks man and to everyone who contributed.
CodePudding user response:
Class com.example.myapplication.Dishes does not define a no-argument constructor.
so Dishes
don't have no-argument constructor, thats correct as you have only one constructor in Dishes
class
public Dishes(String name, float rating, int price) {
so you need yet another with no arguments at all, so
public Dishes() {}
public Dishes(String name, float rating, int price) {
... rest of code
and why this happens? maybe Firebase is using empty constructor for creating a Dishes
object for some internal purposes, but thats guessing...