list view in fragments null pointer exception

Question

I am trying to setup swipe to refresh in my fragment, which fetches objects from parse. But every time, I seem to get an null pointer exception on setadapter and list view. Although both of them are correctly initialized are not null.

My recentsadapter:

package com.astuetz.viewpager.extensions.sample;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.HashMap;

public class RecentsAdapter extends BaseAdapter
{

        LayoutInflater inflater;
        Context context;
        ArrayList<HashMap<String,String>> items = null;

        public RecentsAdapter(Context context,ArrayList<HashMap<String,String>> items)
        {
            super();
            this.context = context;
            this.items = items;
            inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        }

        @Override
        public int getCount()
        {
            return items.size();
        }

        @Override
        public Object getItem(int position)
        {
            return items.get(position);
        }

        @Override
        public long getItemId(int position)
        {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent)
        {
            View v = convertView;
            MyHolder holder = null;
            if(v == null)
            {
                v = inflater.inflate(R.layout.recents_list_item,parent,false);
                holder = new MyHolder(v);
                v.setTag(holder);
            }

            else
            {
                holder = (MyHolder) v.getTag();
            }

            holder.title.setText(items.get(position).get("title"));
            holder.author.setText(items.get(position).get("author"));
            holder.dept.setText(items.get(position).get("dept"));
            holder.price.setText(items.get(position).get("price"));
    //        holder.place.setText(items.get(position).get("place"));


            return v;
        }

        class MyHolder
        {

            TextView dept,title,author,price,place;

            public MyHolder(View view)
            {
                title = (TextView) view.findViewById(R.id.book_title);
                dept = (TextView)view.findViewById(R.id.dept_name);
                author = (TextView) view.findViewById(R.id.author_name);
                price = (TextView)view.findViewById(R.id.price_list);
    //            place = (TextView)view.findViewById(R.id.place_list);
            }

        }
    }

My recent_card.xml which defines my list view and swipe to refresh:

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
             xmlns:card_view="http://schemas.android.com/apk/res-auto"
             android:layout_width="match_parent"
             android:layout_height="match_parent">

    <android.support.v4.widget.SwipeRefreshLayout
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    <android.support.v7.widget.CardView
        android:id="@+id/recents_card"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_margin="8dp"
        card_view:cardBackgroundColor="@android:color/white"
        card_view:cardCornerRadius="8dp"
        android:padding="8dp">

        <ListView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/recents_list"
            android:divider="@color/dividerColor"
            android:dividerHeight="1dp"/>

    </android.support.v7.widget.CardView>
    </android.support.v4.widget.SwipeRefreshLayout>
</FrameLayout>

and my RecentsCardFragment.java which implements them:

/*
 * Copyright (C) 2013 Andreas Stuetz <[email protected]>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.astuetz.viewpager.extensions.sample;

import android.app.AlertDialog;
import android.app.ProgressDialog;
import android.content.Context;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.view.ViewCompat;
import android.support.v4.widget.SwipeRefreshLayout;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Adapter;
import android.widget.ListView;
import android.widget.Toast;


import com.parse.FindCallback;
import com.parse.GetCallback;
import com.parse.Parse;
import com.parse.ParseException;
import com.parse.ParseObject;
import com.parse.ParseQuery;



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



public class RecentsCardFragment extends Fragment implements SwipeRefreshLayout.OnRefreshListener
{
   ListView  recentsList = (ListView)getActivity().findViewById(R.id.recents_list);

    private SwipeRefreshLayout refreshBooks;

     ArrayList<HashMap<String,String>> items = new ArrayList<>();





    //private  ProgressDialog progress;


    public static RecentsCardFragment newInstance() {
        RecentsCardFragment f = new RecentsCardFragment();
            return f;
        }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.recents_card,container,false);
        ViewCompat.setElevation(rootView,50);
        refreshBooks = (SwipeRefreshLayout) rootView.findViewById(R.id.container);
        refreshBooks.setOnRefreshListener(this);


        getBooks();


        RecentsAdapter  adapter = new RecentsAdapter(getActivity().getApplicationContext(), items);

        recentsList.setAdapter(adapter);


        return rootView;
    }


    private ArrayList<HashMap<String,String>> getBooks(){

        final ParseQuery<ParseObject> query = ParseQuery.getQuery("Posted");
        query.orderByDescending("createdAt");

        query.findInBackground(new FindCallback<ParseObject>() {


            @Override
            public void done(List<ParseObject> parseObjects, ParseException e) {


                if (e == null){

                    Log.w("Parse","Inside getbooks()");
                    for (ParseObject book : parseObjects) {

                        HashMap<String, String> test = new HashMap<>();

                        String dept = book.getString("Department");
                        String title = book.getString("Title");
                        String author = book.getString("Author");
                        Number price_num = book.getNumber("Price");
                        String price = String.valueOf(price_num);
                        String place = book.getString("Place");
                        String desp = book.getString("Description");

                        test.put("dept", dept);
                        test.put("title", title);
                        test.put("author", author);
                        test.put("price", price);
                        test.put("place", place);
                        test.put("description", desp);

                        items.add(test);




                    }


                } else {

                    Log.d("Books", "Error: " + e.getMessage());

                }

            }

        });

        return items;
    }


    @Override
    public void onRefresh(){

        refreshBooks.setRefreshing(true);
        updateBooks();



}

    private void updateBooks(){

        Toast.makeText(getActivity(),"Refresh", Toast.LENGTH_SHORT).show();

        items.addAll(getBooks());

      refreshBooks.setRefreshing(false);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

   }


    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

    }


 }

Here is my logcat:

06-14 02:44:52.485    2373-2373/com.astuetz.viewpager.extensions.sample I/Process﹕ Sending signal. PID: 2373 SIG: 9
06-14 02:58:26.624    2502-2524/com.astuetz.viewpager.extensions.sample D/OpenGLRenderer﹕ Render dirty regions requested: true
06-14 02:58:26.644    2502-2502/com.astuetz.viewpager.extensions.sample D/﹕ HostConnection::get() New Host Connection established 0xabb86710, tid 2502
06-14 02:58:27.720    2502-2502/com.astuetz.viewpager.extensions.sample D/Atlas﹕ Validating map...
06-14 02:58:28.692    2502-2502/com.astuetz.viewpager.extensions.sample I/Choreographer﹕ Skipped 57 frames!  The application may be doing too much work on its main thread.
06-14 02:58:28.716    2502-2502/com.astuetz.viewpager.extensions.sample D/AndroidRuntime﹕ Shutting down VM
06-14 02:58:28.720    2502-2502/com.astuetz.viewpager.extensions.sample E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.astuetz.viewpager.extensions.sample, PID: 2502
    java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.support.v4.app.FragmentActivity.findViewById(int)' on a null object reference
            at com.astuetz.viewpager.extensions.sample.RecentsCardFragment.<init>(RecentsCardFragment.java:54)
            at com.astuetz.viewpager.extensions.sample.RecentsCardFragment.newInstance(RecentsCardFragment.java:68)
            at com.astuetz.viewpager.extensions.sample.MainActivity$MyPagerAdapter.getItem(MainActivity.java:133)
            at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:97)
            at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:837)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:987)
            at android.support.v4.view.ViewPager.populate(ViewPager.java:919)
            at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1441)
            at android.view.View.measure(View.java:17430)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:875)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
            at android.view.View.measure(View.java:17430)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
            at android.view.View.measure(View.java:17430)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
            at android.view.View.measure(View.java:17430)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
            at android.view.View.measure(View.java:17430)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
            at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1436)
            at android.widget.LinearLayout.measureVertical(LinearLayout.java:722)
            at android.widget.LinearLayout.onMeasure(LinearLayout.java:613)
            at android.view.View.measure(View.java:17430)
            at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5463)
            at android.widget.FrameLayout.onMeasure(FrameLayout.java:430)
            at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2560)
            at android.view.View.measure(View.java:17430)
            at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2001)
            at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1166)
            at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1372)
            at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1054)
            at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5779)
            at android.view.Choreographer$CallbackRecord.run(Choreographer.java:767)
            at android.view.Choreographer.doCallbacks(Choreographer.java:580)
            at android.view.Choreographer.doFrame(Choreographer.java:550)
            at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:753)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5221)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
06-14 02:58:32.992    2502-2502/com.astuetz.viewpager.extensions.sample I/Process﹕ Sending signal. PID: 2502 SIG: 9

I keep on getting null pointer exceptions to my list view recents list, or at the line, recentslist.ssetadapter(adapter).

Although, there are several answered questions regarding the same topic, in unable to solve mine using them.

please help me out! Thanks in advance!

Answer 1

Your recent_list is null and you are referencing it outside the onCreateView inside your RecentsCardFragment, this is why the NullPointerException happenning. Move your recent_list declaration into your onCreateView method, like this:

public class RecentsCardFragment extends Fragment implements SwipeRefreshLayout.OnRefreshListener
{
   ListView  recentsList;

    private SwipeRefreshLayout refreshBooks;

     ArrayList<HashMap<String,String>> items = new ArrayList<>();

    //private  ProgressDialog progress;

    public static RecentsCardFragment newInstance() {
        RecentsCardFragment f = new RecentsCardFragment();
            return f;
        }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.recents_card,container,false);
        recentsList = (ListView)rootView.findViewById(R.id.recents_list);
        ViewCompat.setElevation(rootView,50);
        refreshBooks = (SwipeRefreshLayout) rootView.findViewById(R.id.container);
        refreshBooks.setOnRefreshListener(this);


        getBooks();


        RecentsAdapter  adapter = new RecentsAdapter(getActivity().getApplicationContext(), items);

        recentsList.setAdapter(adapter);


        return rootView;
    }