So im working on project which shows memes and it loads em from an API, so now theres a main menu to select categories so when i click on a particular category, the fragment transactions to a new fragment and then it loads memes by a method written in ExploreFragment -
package com.example.memeit;
import static com.android.volley.VolleyLog.TAG;
import android.content.Context;
import android.os.Bundle;
import androidx.annotation.NonNull;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.Adapter;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;
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.List;
/**
* A simple {@link Fragment} subclass.
* Use the {@link ExploreFragment#newInstance} factory method to
* create an instance of this fragment.
*/
public class ExploreFragment extends Fragment{
// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;
public String BASEURL = "https://meme-api.herokuapp.com/gimme/30";
public TextView tv1_likes;
public RecyclerView rcv1_explore;
public Context context;
public ArrayList<exploreclass> list;
public boolean isScrolling = false;
public LinearLayoutManager manager;
public explore_adapter adapter;
int currentItems, totalItems, scrolledOutItems;
public ExploreFragment() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment ExploreFragment.
*/
// TODO: Rename and change types and number of parameters
public static ExploreFragment newInstance(String param1, String param2) {
ExploreFragment fragment = new ExploreFragment();
Bundle args = new Bundle();
args.putString(ARG_PARAM1, param1);
args.putString(ARG_PARAM2, param2);
fragment.setArguments(args);
return fragment;
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_explore, container, false);
tv1_likes =(TextView) view.findViewById(R.id.tv1_explore);
list = new ArrayList<>();
manager = new LinearLayoutManager(getContext());
adapter = new explore_adapter(list, getContext());
rcv1_explore =(RecyclerView) view.findViewById(R.id.rcv_explore);
rcv1_explore.setHasFixedSize(true);
rcv1_explore.addOnScrollListener(new RecyclerView.OnScrollListener() {
@Override
public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
if(newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL) {
isScrolling = true;
}
}
@Override
public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
totalItems = manager.getItemCount();
currentItems = manager.getChildCount();
scrolledOutItems = manager.findFirstVisibleItemPosition();
if(isScrolling && (totalItems == currentItems + scrolledOutItems)) {
isScrolling = false;
fetchMoreData();
}
}
});
return view;
}
public void ExtractMemes(Context context, String url) {
RequestQueue queue = Volley.newRequestQueue(context);
JsonObjectRequest response = new JsonObjectRequest(Request.Method.GET, url, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
try {
JSONArray memes_array = response.getJSONArray("memes");
for(int i=0; i<memes_array.length(); i++) {
JSONObject memes_object = memes_array.getJSONObject(i);
exploreclass class_object = new exploreclass();
class_object.setUps(memes_object.getInt("ups"));
class_object.setUrl(memes_object.getString("url"));
class_object.setPostLink(memes_object.getString("postLink"));
list.add(class_object);
}
} catch (JSONException e) {
e.printStackTrace();
}
rcv1_explore.setLayoutManager(manager);
rcv1_explore.setAdapter(adapter);
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(getContext(), error.getLocalizedMessage(), Toast.LENGTH_SHORT).show();
}
});
queue.add(response);
}
private void fetchMoreData() {
RequestQueue queue = Volley.newRequestQueue(getContext());
JsonObjectRequest response = new JsonObjectRequest(Request.Method.GET, BASEURL, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
try {
JSONArray memes_array = response.getJSONArray("memes");
for(int i=0; i<memes_array.length(); i++) {
JSONObject memes_object = memes_array.getJSONObject(i);
exploreclass class_object = new exploreclass();
class_object.setUps(memes_object.getInt("ups"));
class_object.setUrl(memes_object.getString("url"));
class_object.setPostLink(memes_object.getString("postLink"));
list.add(class_object);
adapter.notifyDataSetChanged();
Toast.makeText(getContext(), "Success", Toast.LENGTH_SHORT).show();
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
Toast.makeText(getContext(), error.getLocalizedMessage(), Toast.LENGTH_SHORT).show();
}
});
queue.add(response);
}
}
so now when i call this method ExtractMemes in another class to load memes after transaction it says -
java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.recyclerview.widget.RecyclerView.setLayoutManager(androidx.recyclerview.widget.RecyclerView$LayoutManager)' on a null object reference
at com.example.memeit.ExploreFragment$2.onResponse(ExploreFragment.java:154)
at com.example.memeit.ExploreFragment$2.onResponse(ExploreFragment.java:137)
this is how i access the method -
if(position == 0){
FragmentTransaction transaction = getChildFragmentManager().beginTransaction();
ExploreFragment exploreFragment = new ExploreFragment();
exploreFragment.list = new ArrayList<>();
exploreFragment.manager = new LinearLayoutManager(getContext());
transaction.replace(R.id.framelayout, exploreFragment);
exploreFragment.ExtractMemes(getContext(), "https://meme-api.herokuapp.com/gimme/HistoryMemes/50");
}
