Why is my recyclerView not displaying any data?

Question

I have implemented a RecyclerView and customer Adapter many times, but for some reason I cannot get this one to display any data. I am feeding in data from JSON using retrofit and calling notifyDataSetChanged() once this has been loaded, yet it still remains blank. I have stripped this back to just one text view to try and simplify but still not getting anything. Can anyone see where I am going wrong here?

When I debug, I am getting the List to contain data so I am definitely parsing the data correctly, I just cant get it display in the recycler view. I have even checked the list.size() in the loadTrailerList method and it has data.

My Activity onCreate method:

trailerAdapter = new TrailerAdapter(this);
trailerRecyclerView = findViewById(R.id.trailer_recycler_view);
trailerRecyclerView.setLayoutManager(new LinearLayoutManager(this));
trailerRecyclerView.setAdapter(trailerAdapter);

Retrofit onResponse method:

if (response.body() != null) {
                trailers = response.body().getTrailers();
            }
            trailerAdapter.loadTrailerList(response.body().getTrailers());

My custom adapter:

public class TrailerAdapter extends RecyclerView.Adapter<TrailerAdapter.TrailerViewHolder> {

    private final List<Trailer> trailerList = new ArrayList<>();
    private final TrailerClickListener listener;

    public TrailerAdapter(TrailerClickListener listener) {
        this.listener = listener;
    }

    @NonNull
    @Override
    public TrailerViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View itemView = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.trailer_list_item, viewGroup, false);
        return new TrailerViewHolder(itemView, this);
    }

    @Override
    public void onBindViewHolder(@NonNull TrailerViewHolder trailerViewHolder, int i) {
        trailerViewHolder.trailerTitle.setText(trailerList.get(i).getName());
    }

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

    public void loadTrailerList(List<Trailer> trailers) {
        this.trailerList.clear();
        if (trailers != null) {
            trailers.addAll(trailers);
        }
        notifyDataSetChanged();
    }

    class TrailerViewHolder extends RecyclerView.ViewHolder {

        final TrailerAdapter trailerAdapter;
        private final TextView trailerTitle;

        private TrailerViewHolder(@NonNull View itemView, TrailerAdapter trailerAdapter) {
            super(itemView);
            this.trailerAdapter = trailerAdapter;
            trailerTitle = itemView.findViewById(R.id.text_view_trailer_title);

            itemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    listener.onTrailerClicked(trailerList.get(getAdapterPosition()));
                }
            });
        }
    }
}

My List Item XML

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content">

            <TextView
                android:id="@+id/text_view_trailer_title"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="Play Trailer" />

</LinearLayout>

the recycler view in my activity XML:

                    <android.support.v7.widget.RecyclerView
                        android:id="@+id/trailer_recycler_view"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content"
                        android:background="@color/colorPrimary"
                        app:layout_constraintTop_toBottomOf="@+id/trailer_divider">

                    </android.support.v7.widget.RecyclerView>

I am grateful for anyone that can point me in the right direction

Answer 1

MainActivity.kt-

package com.example.groc

import android.content.Intent
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView


class MainActivity : AppCompatActivity() {

    private lateinit var recyclerView: RecyclerView
    private lateinit var foodList : ArrayList<food>
    private lateinit var FoodAdapter: foodAdapter

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)


        recyclerView = findViewById(R.id.recyclerView)
        recyclerView.setHasFixedSize(true)
        recyclerView.layoutManager=LinearLayoutManager(this)

        foodList= ArrayList()


        foodList.add(food(R.drawable.pasta,"Pasta"))
        foodList.add(food(R.drawable.chicken,"Chicken"))
        foodList.add(food(R.drawable.panner,"Paneer"))
        foodList.add(food(R.drawable.rajma,"Rajma"))



        FoodAdapter= foodAdapter(foodList)
        recyclerView.adapter=FoodAdapter


        FoodAdapter.onItemClick = {

            val intent =Intent(this,DetailedActivity::class.java)
            intent.putExtra("food",it)
            startActivity(intent)
        }
    }

}

foodAdapter.kt-

package com.example.groc

import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.ImageView
import android.widget.TextView
import androidx.recyclerview.widget.RecyclerView


class foodAdapter(private val foodList:ArrayList<food>)
    :RecyclerView.Adapter<foodAdapter.FoodViewHolder>(){

var onItemClick : ((food) -> Unit)? =null

    class FoodViewHolder(itemView: View):RecyclerView.ViewHolder(itemView){
        val imageView : ImageView =itemView.findViewById(R.id.imageView)
        val textView : TextView =itemView.findViewById(R.id.textView)


    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): FoodViewHolder {

        val view = LayoutInflater.from(parent.context).inflate(R.layout.each_item,parent,false)
        return FoodViewHolder(view)
    }

    override fun getItemCount(): Int {

        return foodList.size
    }

    override fun onBindViewHolder(holder: FoodViewHolder, position: Int) {

        val food=foodList[position]
        holder.imageView.setImageResource(food.image)
        holder.textView.text=food.name

        holder.itemView.setOnClickListener {
            onItemClick?.invoke(food)
        }

    }
}

food.kt-

package com.example.groc

import android.os.Parcel
import android.os.Parcelable

data class food(val image:Int , val name: String) : Parcelable {
    constructor(parcel: Parcel) : this(
        parcel.readInt(),
        parcel.readString()!!
    ) {
    }

    override fun writeToParcel(parcel: Parcel, flags: Int) {
        parcel.writeInt(image)
        parcel.writeString(name)
    }

    override fun describeContents(): Int {
        return 0
    }

    companion object CREATOR : Parcelable.Creator<food> {
        override fun createFromParcel(parcel: Parcel): food {
            return food(parcel)
        }

        override fun newArray(size: Int): Array<food?> {
            return arrayOfNulls(size)
        }
    }

}

DetailedActivity.kt-

package com.example.groc

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.ImageButton
import android.widget.ImageView
import android.widget.TextView
import android.widget.Toast

class DetailedActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_detailed)

        val food = intent.getParcelableExtra<food>("food")
        if(food!=null)
        {
            val textView: TextView=findViewById(R.id.detailedActivityTV)
            val imageView: ImageView=findViewById(R.id.detailedActivityIV)

            textView.text=food.name
            imageView.setImageResource(food.image)

            Toast.makeText(this,textView.text,Toast.LENGTH_SHORT).show()


        }
    }
}

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">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="0dp"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.5" />
</androidx.constraintlayout.widget.ConstraintLayout>

each_item.xml-

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    app:cardCornerRadius="20dp"
    android:layout_marginHorizontal="10dp"
    android:layout_marginVertical="16dp"
    app:cardElevation="4dp">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <ImageView
            android:id="@+id/imageView"
            android:layout_width="120dp"
            android:layout_height="100dp"
            android:scaleType="fitXY"
            android:src="@drawable/pasta"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"/>

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Pasta"
            android:textColor="@color/black"
            android:textSize="24sp"
            android:textStyle="bold"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:flow_horizontalBias="0.5"
            app:layout_constraintStart_toEndOf="@id/imageView"
            app:layout_constraintTop_toTopOf="parent"/>
    </androidx.constraintlayout.widget.ConstraintLayout>
</androidx.cardview.widget.CardView>

activity_detailed.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=".DetailedActivity">

    <ImageView
        android:id="@+id/detailedActivityIV"
        android:layout_width="0dp"
        android:layout_height="250dp"
        android:scaleType="fitXY"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@drawable/pasta" />

    <TextView
        android:id="@+id/detailedActivityTV"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginTop="16dp"
        android:text="TextView"
        android:textSize="24sp"
        android:textStyle="bold"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/detailedActivityIV" />
</androidx.constraintlayout.widget.ConstraintLayout>

Answer 2

It is because you are sending a list to adapter but, you are not initializing your list which is used in the adapter.

try this.

public void loadTrailerList(List<Trailer> trailers) {
        this.trailerList.clear();
        if (trailers != null) {
            trailerList = trailers;
        }
        notifyDataSetChanged();
    }

Answer 3

Doh! I just realised what I was doing wrong:

In my loadTrailerList() method in my adapter, I was calling:

trailers.addAll(trailers);

instead of:

trailerList.addAll(trailers);

to load the list of items into the actual ArrayList! whoops!