CS50 Android Track Filter will not run in device despite building without errors

I am trying to implement the filter function in the Pokedex app, and although the app "Builds" without any errors, when I go to run it within the virtual Android phone, I get the error "Pokedex Keeps Stopping," on the virtual device. Since my code builds correctly, I cannot really figure out why it would continue to crash on the virtual device. Any help will be appreciated!

Here is my PokedexAdapter.java file, with the filter function added at the bottom:

package edu.harvard.cs50.pokedex;
import android.content.Context;
import android.content.Intent;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Filter;
import android.widget.Filterable;
import android.widget.LinearLayout;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.Volley;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Hashtable;
import java.util.List;
public class PokedexAdapter extends RecyclerView.Adapter<PokedexAdapter.PokedexViewHolder> implements Filterable {
public static class PokedexViewHolder extends RecyclerView.ViewHolder {
public LinearLayout containerView;
public TextView textView;
PokedexViewHolder(View view) {
super(view);
containerView = view.findViewById(R.id.pokedex_row);
textView = view.findViewById(R.id.pokedex_row_text_view);
containerView.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Pokemon current = (Pokemon) containerView.getTag();
Intent intent = new Intent(v.getContext(), PokemonActivity.class);
intent.putExtra("url", current.getUrl());
v.getContext().startActivity(intent);
}
});
}
}
private List<Pokemon> pokemon = new ArrayList<>();
private RequestQueue requestQueue;
PokedexAdapter(Context context) {
requestQueue = Volley.newRequestQueue(context);
loadPokemon();
}
public void loadPokemon() {
String url = "https://pokeapi.co/api/v2/pokemon?limit=151";
JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, url, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
try {
JSONArray results = response.getJSONArray("results");
for (int i = 0; i < results.length(); i++) {
JSONObject result = results.getJSONObject(i);
String name = result.getString("name");
pokemon.add(new Pokemon(
name.substring(0, 1).toUpperCase() + name.substring(1),
result.getString("url")
));
}
notifyDataSetChanged();
} catch (JSONException e) {
Log.e("cs50", "Json error", e);
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Log.e("cs50", "Pokemon list error", error);
}
});
requestQueue.add(request);
}
@NonNull
@Override
public PokedexViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext())
.inflate(R.layout.pokedex_row, parent, false);
return new PokedexViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull PokedexViewHolder holder, int position) {
Pokemon current = pokemon.get(position);
holder.textView.setText(current.getName());
holder.containerView.setTag(current);
}
@Override
public int getItemCount() {
return pokemon.size();
}
@Override
public Filter getFilter() {
return new PokemonFilter();
}
private class PokemonFilter extends Filter {
@Override
protected FilterResults performFiltering(CharSequence constraint) {
// implement your search here!
FilterResults results = new FilterResults();
if (constraint == null || constraint.length() == 0) {
//returns whole list if nothing is entered
results.values = pokemon;
results.count = pokemon.size();
}
else {
List<Pokemon> filteredPokemon = new ArrayList<>();
for (Pokemon name : pokemon) {
if (name.getName().toUpperCase().startsWith(constraint.toString().toUpperCase())) {
filteredPokemon.add(name);
results.values = filteredPokemon; // you need to create this variable!
results.count = filteredPokemon.size();
}
}
}
return results;
}
@Override
protected void publishResults(CharSequence constraint, FilterResults results) {
List<Pokemon> filtered = (List<Pokemon>) results.values;
notifyDataSetChanged();
}
}
}

And here is how it is implemented in MainActivity.java:

package edu.harvard.cs50.pokedex;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.SearchView;
public class MainActivity extends AppCompatActivity implements SearchView.OnQueryTextListener {
private RecyclerView recyclerView;
private PokedexAdapter adapter;  //private RecyclerView.Adapter adapter;
private RecyclerView.LayoutManager layoutManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.recycler_view);
adapter = new PokedexAdapter(getApplicationContext());
layoutManager = new LinearLayoutManager(this);
recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(layoutManager);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main_menu, menu);
MenuItem searchItem = menu.findItem(R.id.action_search);
SearchView searchView = (SearchView) searchItem.getActionView();
searchView.setOnQueryTextListener(this);
return true;
}
@Override
public boolean onQueryTextChange(String newText) {
adapter.getFilter().filter(newText);
return false;
}
@Override
public boolean onQueryTextSubmit(String newText) {
adapter.getFilter().filter(newText);
return false;
}
}

@Override
public void onBindViewHolder(@NonNull PokedexViewHolder holder, int position) {
if (filtered.isEmpty()) {
Pokemon current = pokemon.get(position);
holder.textView.setText(current.getName());
holder.containerView.setTag(current);
}else{
Pokemon current = filtered.get(position);
holder.textView.setText(current.getName());
holder.containerView.setTag(current);
}
}
@Override
public int getItemCount() {
if (filtered.isEmpty()) {
return pokemon.size();
}else {
return filtered.size();
}
}

use this instead in your pokedex adapter

I had a similar issue which was caused by the following :

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

I believe it can happen that pokemon is not initiated and therefore doesn't have a return value (or equals "null")

I added an if statement that would just return 0 if pokemon is null

@Override
public int getItemCount() {
if (pokemon != null) {
return pokemon.size();
} else {
return 0;
} 
}

I also have changed the variable name pokemon to the variable name of my Array List that holds the filtered items.

The issue (may) be in your imports. You have:

import android.widget.SearchView;

In your MainActivity. When I changed that import over to the following:

import androidx.appcompat.widget.SearchView;

Everything seemed to work. If that doesn't work, then I have no idea.

Other thing you have to do is change the variable "pokemon" in onBindViewHolder and in getItemCount to the variable you stored the filtered data called "filtered".

And it's mandatory to change import android.widget.SearchView; as the other person said.

cs50 advised to use

@Override
protected void publishResults(CharSequence charSequence, FilterResults results) {
filtered = (List<Pokemon>) results.values;
notifyDataSetChanged();
}

but if you notice, android studio prompts you that filtered was never used by highlighting filtered in grey.

I have been studying the code trying to figure out where the problem was. The fact that the code compiles and runs without any errors just means that the filtering was executed successfully (honestly I'm not 100% sure, I am just guessing) but for some reason the search result was not displayed.

After noticing that filtered was greyed out, I tried my luck and replaced filtered with pokemon because the original list that was posted is pokemon.

What I ended up with was

@Override
protected void publishResults(CharSequence charSequence, FilterResults results) {
pokemon = (List<Pokemon>) results.values;
notifyDataSetChanged();
}

and now everything works fine.

Also I did update my imports like what the second answer suggested