Null Pointer Exception in getView() of custom adapter while extending array adapter

Question

I am trying to display JSON data but it's giving null pointer exception. It can't get the context of custom single item that I'm inflating

public class HotelAdapter extends ArrayAdapter{
    private List<HotelModel> hotelModelList;
    private LayoutInflater layoutInflater;
    private int resource;

    public HotelAdapter(@NonNull Context context, int resource, @NonNull 
List<HotelModel> objects) {
        super(context, resource, objects);
        hotelModelList = objects;
        this.resource=resource;
        layoutInflater = 
(LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);
    }

    @NonNull
    @Override
    public View getView(int position, @Nullable View convertView, @NonNull 
ViewGroup parent) {
        ViewHolder holder = null;
        if (convertView==null){
            holder =new ViewHolder();
            convertView = layoutInflater.inflate(R.layout.item_hotel,null);

            holder.addr = 
(TextView)convertView.findViewById(R.id.hotel_add_mini);
            holder.categ = 
(TextView)convertView.findViewById(R.id.hotel_rating);
            holder.name = 
(TextView)convertView.findViewById(R.id.hotel_name);
            holder.price = 
(TextView)convertView.findViewById(R.id.hotel_price);
            holder.rating = 
(RatingBar)convertView.findViewById(R.id.ratingBar2);

        }
        else {
            holder= (ViewHolder) convertView.getTag();
        }


        holder.addr.setText(hotelModelList.get(position).getAddr());
        holder.categ.setText(hotelModelList.get(position).getCateg());
        holder.name.setText(hotelModelList.get(position).getName());
        holder.price.setText(Integer.toString(hotelModelList.get(position).getPrice()));
        holder.rating.setRating(hotelModelList.get(position).getRating());


        return convertView;
    }
    class ViewHolder{
        private ImageView img;
        private TextView name;
        private TextView addr;
        private TextView categ;
        private TextView price;
        private RatingBar rating;
    }
}

It can't get the reference of TextViews from item_hotel.xml layout files. So It's giving null pointer exception. I have checked the List<>, the list is non null so it's just the reference problem. Moreover, in this

holder.addr = 
(TextView)convertView.findViewById(R.id.hotel_add_mini);

The (TextView) is showing redundant but it shouldn't have as findViewById returns a view and we have to cast it into textView.

Answer 1

You forgot to set the tag in your if condition and your're using tag in else condition that is the problem.

In your if condition add,

convertView.setTag(holder);

Answer 2

Basically the problem is in this line

layoutInflater = (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);

try to use context which you are getting in constructor of your HotelAdapter

layoutInflater = (LayoutInflater)context.getSystemService(LAYOUT_INFLATER_SERVICE);

and set tag on convertView

if (convertView == null) {
            convertView = mInflater.inflate(R.layout.item_hotel, null);
            holder = new ViewHolder();
            holder.addr = (TextView) convertView.findViewById(R.id.hotel_add_mini);
            holder.categ = (TextView) convertView.findViewById(R.id.hotel_rating);
            holder.name = (TextView) convertView.findViewById(R.id.hotel_name);
            holder.price = (TextView) convertView.findViewById(R.id.hotel_price);
            holder.rating = (RatingBar) convertView.findViewById(R.id.ratingBar2);
            convertView.setTag(holder);
        } else{
            holder= (ViewHolder) convertView.getTag();
        }

Answer 3

Replace this:

private List<HotelModel> hotelModelList;
private LayoutInflater layoutInflater;
private int resource;

with:

private List<HotelModel> hotelModelList;
private LayoutInflater layoutInflater;
private int resource;
private Context context;

then update your constructor and instead of this:

public HotelAdapter(@NonNull Context context, int resource, @NonNull 
List<HotelModel> objects) 
{
    super(context, resource, objects);
    hotelModelList = objects;
    this.resource=resource;
    layoutInflater =
    (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);
}

Use following:

public HotelAdapter(@NonNull Context context, int resource, @NonNull 
List<HotelModel> objects) 
{
    super(context, resource, objects);
    this.hotelModelList = objects;
    this.resource=resource;
    this.context = context;
}

After that instead of following line:

convertView = layoutInflater.inflate(R.layout.item_hotel,null);

Use following two lines:

LayoutInflater inflater = ((Activity) context).getLayoutInflater();
convertView = inflater.inflate(R.layout.item_hotel, parent, false);

Remove following line also:

layoutInflater = (LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE);

This will solve your issue you need to provide context to your layout inflater I think that might be the problem in your case.

Answer 4

Try to make a constructor and set context also.

      public class HotelAdapter extends ArrayAdapter{
           Context mcontext;
           private List<HotelModel> mhotelModelList;

           public HotelAdapter(Context context, private List<HotelModel> hotelModelList;){                 
                                super(context, R.layout.item_hotel, hotelModelList);
                                this.mcontext = context;
                                this.mhotelModelList = hotelModelList;
                            }

          @Override
          public View getView(int position, View convertView, ViewGroup parent) {
                    LayoutInflater vi = (LayoutInflater) 
                   mcontext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            if (convertView == null) {
                 convertView = mInflater.inflate(R.layout.item_hotel, null);
                 holder = new ViewHolder();
                  holder.addr =(TextView)convertView.findViewById(R.id.hotel_add_mini);         
                 convertView.setTag(holder);
         }

        else{
        holder = (ViewHolder) convertView.getTag();

          holder.addr.setText(hotelModelList.get(position).getAddr());
         return convertView;
     }
   }