Android app runtime error at onCreate() method of fragment

Question

I'm developing a music player app for Android. I've only created an Activity with 4 fragments with empty layouts using ViewPager. It works great upto this point.

The fragments are Artists, Albums, All Songs and Playlists.

Now, I'm trying to fill the All Songs fragment with a list of all songs on the device. I've added the necessary code for that and the app compiles without any error. However, when I open the app, I get a force close with the message "Unfortunately, Player has stopped". So Here's the logcat.

E/AndroidRuntime( 2539): FATAL EXCEPTION: main
E/AndroidRuntime( 2539): java.lang.NullPointerException
E/AndroidRuntime( 2539):     at com.example.player.AllSongsFragment.onCreate(AllSongsFragment.java:26)
E/AndroidRuntime( 2539):     at android.support.v4.app.Fragment.performCreate(Fragment.java:1477)
E/AndroidRuntime( 2539):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:904)
E/AndroidRuntime( 2539):     at android.support.v4.app.FragmentManagerImpl.performPendingDeferredStart(FragmentManager.java:834)
E/AndroidRuntime( 2539):     at android.support.v4.app.Fragment.setUserVisibleHint(Fragment.java:841)
E/AndroidRuntime( 2539):     at android.support.v4.app.FragmentPagerAdapter.setPrimaryItem(FragmentPagerAdapter.java:130)
E/AndroidRuntime( 2539):     at android.support.v4.view.ViewPager.populate(ViewPager.java:1066)
E/AndroidRuntime( 2539):     at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
E/AndroidRuntime( 2539):     at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1436)
E/AndroidRuntime( 2539):     at android.view.View.measure(View.java:15775)
E/AndroidRuntime( 2539):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4942)
E/AndroidRuntime( 2539):     at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
E/AndroidRuntime( 2539):     at android.view.View.measure(View.java:15775)
E/AndroidRuntime( 2539):     at android.widget.LinearLayout.measureVertical(LinearLayout.java:850)
E/AndroidRuntime( 2539):     at android.widget.LinearLayout.onMeasure(LinearLayout.java:588)
E/AndroidRuntime( 2539):     at android.view.View.measure(View.java:15775)
E/AndroidRuntime( 2539):     at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4942)

So, the problem is a NullPointerException in the onCreate method of the AllSongsFragment class

Here's the content of AllSongsFragment.java

package com.example.player;

import com.example.player.R;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import android.net.Uri;
import android.content.ContentResolver;
import android.database.Cursor;
import android.widget.ListView;
import com.example.player.adapter.AllSongsAdapter;
import com.example.player.Song;

public class AllSongsFragment extends Fragment {
    private ArrayList<Song> songArray;
    private ListView songListView;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        songListView = (ListView)getView().findViewById(R.id.all_songs_list);
        songArray = new ArrayList<Song>();
        getSongList();
        // Sort the songs
        Collections.sort(songArray, new Comparator<Song>() {
            public int compare(Song a, Song b) {
                return a.getTitle().compareTo(b.getTitle());
            }
        });
        AllSongsAdapter songAdt = new AllSongsAdapter(getActivity(), songArray);
        songListView.setAdapter(songAdt);
    } // onCreate
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.all_songs_fragment_layout, container, false);
        return rootView;
    } //onCreateView()

    public void getSongList() {
    //retrieve song info
         ContentResolver musicResolver = getActivity().getContentResolver();
        Uri musicUri = android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
        Cursor musicCursor = musicResolver.query(musicUri, null, null, null, null);
        // Iterate over the List
        if(musicCursor!=null && musicCursor.moveToFirst()) {
        //get columns
        int titleColumn = musicCursor.getColumnIndex(android.provider.MediaStore.Audio.Media.TITLE);
        int idColumn = musicCursor.getColumnIndex(android.provider.MediaStore.Audio.Media._ID);
        int artistColumn = musicCursor.getColumnIndex(android.provider.MediaStore.Audio.Media.ARTIST);
        //add songs to list
        do {
        long thisId = musicCursor.getLong(idColumn);
        String thisTitle = musicCursor.getString(titleColumn);
        String thisArtist = musicCursor.getString(artistColumn);
        songArray.add(new Song(thisId, thisTitle, thisArtist));
        }  while (musicCursor.moveToNext());
        } // if
    } //getSongList()
} //AllSongsFragment

I have a Song class in Song.java to represent each song object.

package com.flairsome.player;

public class Song {
    private long id;
    private String title;
    private String artist;
    //Constructor
    public Song(long songID, String songTitle, String songArtist) {
        id=songID;
        title=songTitle;
        artist=songArtist;
    }
    // get methods
    public long getID() {
        return id;
    }
    public String getTitle() {
         return title;
    }
    public String getArtist() {
        return artist;
    }
} //.Song

The AllSongsAdapter.java is

package com.example.player.adapter;

import android.widget.BaseAdapter;
import java.util.ArrayList;
import android.content.Context;
import android.view.LayoutInflater;
import android.widget.LinearLayout;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import com.example.player.Song;
import com.example.player.R;

public class AllSongsAdapter extends  BaseAdapter {
    private ArrayList<Song> songs;
    private LayoutInflater songInf;
    // constructor
    public AllSongsAdapter(Context c, ArrayList<Song> theSongs){
        songs = theSongs;
        songInf = LayoutInflater.from(c);
    }
    @Override
    public int getCount() {
        return songs.size();
    }
    @Override
    public Object getItem(int arg0) {
    // TODO Auto-generated method stub
        return null;
    }
    @Override
    public long getItemId(int arg0) {
        // TODO Auto-generated method stub
        return 0;
    }
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        //map to song layout
        LinearLayout songLay = (LinearLayout)songInf.inflate(R.layout.song_item_layout, parent, false);
        //get title and artist views
        TextView songView = (TextView)songLay.findViewById(R.id.song_title);
        TextView artistView = (TextView)songLay.findViewById(R.id.song_artist);
        //get song using position
        Song currSong = songs.get(position);
        //get title and artist strings
        songView.setText(currSong.getTitle());
        artistView.setText(currSong.getArtist());
        //set position as tag
        songLay.setTag(position);
        return songLay;
    } //getView()
}

Although I've posted huge chunka of code, the problem, as seen from the logcat, seems to be in the onCreate() method in the AllSongsFragment class.

Is there anything that I am doing wrong?

Please leave a comment if you need more information or if I need to improve the question. Thank you.

Answer 1

Move this

 songListView = (ListView)getView().findViewById(R.id.all_songs_list);

to onActivityCreated

getView() returns null in your case. songListView is null and you when you set adapter to listview results in NUllPointerException

You can move the below also to onActivityCreated

  songArray = new ArrayList<Song>();
  getSongList();
    // Sort the songs
  Collections.sort(songArray, new Comparator<Song>() {
        public int compare(Song a, Song b) {
            return a.getTitle().compareTo(b.getTitle());
        }
  });
  AllSongsAdapter songAdt = new AllSongsAdapter(getActivity(), songArray);
  songListView.setAdapter(songAdt);

Answer 2

Replace songListView = (ListView)getView().findViewById(R.id.all_songs_list); with songListView = (ListView)findViewById(R.id.all_songs_list);