null pointer exception on getApplicationContext()

Question

I tried the following code with extend activity it worked perfect but now i changed the code to work with extending fragment. I search thorugh internet and found getActivity() function to call query() and other functions. I tried this but now it gives an error saying:

Error

 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.admin.funtube_mp4/com.example.admin.funtube_mp4.Main}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2404)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2464)
            at android.app.ActivityThread.access$900(ActivityThread.java:172)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:146)
            at android.app.ActivityThread.main(ActivityThread.java:5653)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.example.admin.funtube_mp4.HomeFragmant.init_phone_video_grid(HomeFragmant.java:65)
            at com.example.admin.funtube_mp4.HomeFragmant.onCreateView(HomeFragmant.java:49)
            at android.app.Fragment.performCreateView(Fragment.java:1700)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:890)
            at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1062)
            at android.app.BackStackRecord.run(BackStackRecord.java:684)
            at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1453)
            at android.app.Activity.performStart(Activity.java:5550)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2377)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2464)
            at android.app.ActivityThread.access$900(ActivityThread.java:172)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1308)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:146)
            at android.app.ActivityThread.main(ActivityThread.java:5653)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1291)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1107)
            at dalvik.system.NativeStart.main(Native Method)

code

public class HomeFragmant extends Fragment{
    private Cursor videocursor;
    private int video_column_index;
    ListView videolist;

    List<String> listpath = new ArrayList<String>();
    String[] paths=new String[100];
    int count;
    String[] thumbColumns = { MediaStore.Video.Thumbnails.DATA, MediaStore.Video.Thumbnails.VIDEO_ID };
    String path;
    File file;

    public HomeFragmant() {
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.fragment_home, container, false);
        videolist = (ListView) getActivity(). findViewById(R.id.PhoneVideoList);
        init_phone_video_grid();

        return rootView;

    }
    private void init_phone_video_grid() {
        System.gc();
        String[] proj = { MediaStore.Video.Media._ID, MediaStore.Video.Media.DATA, MediaStore.Video.Media.DISPLAY_NAME, MediaStore.Video.Media.SIZE };

      //  file = new File(Environment.getExternalStorageDirectory() + File.separator + "Funtube/UserData/Videos/");
       // videocursor =getActivity().getContentResolver().query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, proj, MediaStore.Images.Media.DATA + " LIKE ? ", new String[]{"%" + file.getAbsolutePath().toString() + "%"}, null);
        videocursor = getActivity().getContentResolver().query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI,proj, null, null, null);
//        videocursor =getActivity().managedQuery(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, proj, MediaStore.Images.Media.DATA + " LIKE ? ", new String[]{"%" + file.getAbsolutePath().toString() + "%"}, null);

        count = videocursor.getCount();

        videolist.setAdapter(new VideoAdapter(getActivity().getApplicationContext()));
        videolist.setOnItemClickListener(videogridlistener);
    }

    private AdapterView.OnItemClickListener videogridlistener = new AdapterView.OnItemClickListener() {
        public void onItemClick(AdapterView parent, View v, int position,long id) {
            System.gc();
            video_column_index = videocursor.getColumnIndexOrThrow(MediaStore.Video.Media.DATA);
            videocursor.moveToPosition(position);
            String filename = videocursor.getString(video_column_index);
            Intent intent = new Intent(getActivity(),ViewVideo.class);
            intent.putExtra("videofilename", filename);
            startActivity(intent);
        }
    };

    public class VideoAdapter extends BaseAdapter {
        private Context vContext;

        public VideoAdapter(Context c) {
            vContext = c;
        }

        public int getCount() {
            return count;
        }

        public Object getItem(int position) {
            return position;
        }

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

        public View getView(int position, View convertView, ViewGroup parent) {
            System.gc();
            ViewHolder holder;
            String id = null;
            convertView = null;
            if (convertView == null) {
                convertView = LayoutInflater.from(vContext).inflate(R.layout.listitem, parent, false);
                holder = new ViewHolder();
                holder.txtTitle = (TextView) convertView.findViewById(R.id.txtTitle);
                holder.txtSize = (TextView) convertView.findViewById(R.id.txtSize);
                holder.thumbImage = (ImageView) convertView.findViewById(R.id.imgIcon);

                video_column_index = videocursor.getColumnIndexOrThrow(MediaStore.Video.Media.DISPLAY_NAME);
                videocursor.moveToPosition(position);
                id = videocursor.getString(video_column_index);
                video_column_index = videocursor.getColumnIndexOrThrow(MediaStore.Video.Media.SIZE);
                videocursor.moveToPosition(position);
                // id += " Size(KB):" +
                // videocursor.getString(video_column_index);
                holder.txtTitle.setText(id);
                holder.txtSize.setText(" Size(KB):"+ videocursor.getString(video_column_index));

                String[] proj = { MediaStore.Video.Media._ID, MediaStore.Video.Media.DISPLAY_NAME, MediaStore.Video.Media.DATA };
                @SuppressWarnings("deprecation")
                Cursor cursor = getActivity().getContentResolver().query(MediaStore.Video.Media.EXTERNAL_CONTENT_URI, proj, MediaStore.Video.Media.DISPLAY_NAME + "=?", new String[]{id}, null);
                cursor.moveToFirst();
                long ids = cursor.getLong(cursor
                        .getColumnIndex(MediaStore.Video.Media._ID));

                ContentResolver crThumb = getActivity().getContentResolver();
                BitmapFactory.Options options = new BitmapFactory.Options();
                options.inSampleSize = 1;
                Bitmap curThumb = MediaStore.Video.Thumbnails.getThumbnail(
                        crThumb, ids, MediaStore.Video.Thumbnails.MICRO_KIND,
                        options);
                holder.thumbImage.setImageBitmap(curThumb);
                curThumb = null;

            } /*
             * else holder = (ViewHolder) convertView.getTag();
             */
            return convertView;
        }
    }

    static class ViewHolder {

        TextView txtTitle;
        TextView txtSize;
        ImageView thumbImage;
    }
}

Answer 1

Do not call getActivity() in onCreateView , you have no guarantee that the Activity is fully created there. Use the onActivityCreated method to get a reference to your Activity .

And unless you're afraid of leaking the Activity , you could just use getActivity() , no need to retrieve the ApplicationContext to create your Adapter IMHO.

From the docs about Fragments :

Caution: If you need a Context object within your Fragment, you can call getActivity(). However, be careful to call getActivity() only when the fragment is attached to an activity. When the fragment is not yet attached, or was detached during the end of its lifecycle, getActivity() will return null.

Answer 2

完全同意@ 2Dee，也许您只需要尝试使用getActivity（）

videolist.setAdapter(new VideoAdapter(getActivity()));