Question

Im building an listview with sections. i was using this answer of a post and asked a question before, but am stuck again. I think it is a pretty weird error.

When i start my activity, i can see the list on the screen, just as i want it. But the moment i try to start scrolling the activity crashes. I thought i implemented everything the same way, but apparently im not.
My adapter:

public class DelftAdapter extends BaseAdapter {
    
    
    private static final int TYPE_ITEM = 0;
    private static final int TYPE_SECTION = 1;
    private Activity activity;
    private  List<ListItem> listItems;
    private static LayoutInflater inflater=null;
    public ImageLoader imageLoader; 
    private final int[] bgColors = new int[] { R.color.list_odd, R.color.list_even };

    
    public DelftAdapter(Activity a, ArrayList<ListItem> li) {
        activity = a;
        listItems = li;
        inflater = (LayoutInflater)activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        imageLoader=new ImageLoader(activity.getApplicationContext());

    }

    public int getCount() {
        return listItems.size();
    }

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

    public long getItemId(int position) {
        return position;
    }
  
    @Override
    public int getItemViewType(int position) {
        return listItems.get(position).isSection() ? TYPE_SECTION : TYPE_ITEM;
    }

    @Override
    public int getViewTypeCount() {
        return 2;  // sectionheader and regular item
    }
   
    
    public View getView(int position, View convertView, ViewGroup parent) {
        int type = getItemViewType(position);
        View vi=convertView;
            final ListItem li = listItems.get(position);
            ItemViewHolder itemHolder;
            SectionViewHolder sectionHolder;
  
             switch (type) {
             case TYPE_SECTION: // is sectionheader
                 if (vi == null) { //convertview==null
                sectionHolder = new SectionViewHolder();
                vi = inflater.inflate(R.layout.sectionedlistitem, null);
                vi.setOnClickListener(null);
                vi.setOnLongClickListener(null);
                vi.setLongClickable(false);
                sectionHolder.title = (TextView) vi.findViewById(R.id.list_header_title);
               }else{//convertview is not null
                   sectionHolder = (SectionViewHolder)vi.getTag();
               }
                   SectionItem si = (SectionItem)li;
                   sectionHolder.title.setText(si.getTitle());
                break;
             case TYPE_ITEM:// no sectionheader
                if (vi == null) { //convertview==null
                    itemHolder = new ItemViewHolder();
                    vi = inflater.inflate(R.layout.singlelistitem, null);
                    itemHolder.name=(TextView)vi.findViewById(R.id.tvname);
                    itemHolder.tip=(TextView)vi.findViewById(R.id.tvtip);
                    itemHolder.image=(ImageView)vi.findViewById(R.id.image);
                }else{  // convertview != null
                    itemHolder = (ItemViewHolder)vi.getTag();
                }
                ListData ld = (ListData)li;
                itemHolder.name.setText(ld.name);
                itemHolder.tip.setText(ld.tip);
                        if (ld.photoUrl != null ){
                            imageLoader.DisplayImage(ld.photoUrl, itemHolder.image);
                        }else{
                            itemHolder.image.setImageURI(Uri.fromFile(new File("//assets/nopic.png")));
                        }
                        // alternating colors
                    int colorPos = position % bgColors.length;
                    vi.setBackgroundResource(bgColors[colorPos]);
                    break;
                 }
            
            
        return vi;
    
}
    public static class SectionViewHolder {
        public TextView title;
    }
    
    public static class ItemViewHolder {
        public TextView name;
        public TextView tip;
        public ImageView image;
    }
    
}

I build two ViewHolders for the two different kind of views. The error that occurs is NullPointerException on the itemHolder.name.setText(ld.name); line.
The thing i don’t get is that the code works for the first few entrys but fails when i start scrolling. In the data i’m using, name and tip are never empty, only photoUrl might be but that is covered in the code.

Anyone knows why this piece of code is failing?

Answer 1

In the code paths where you create a new viewholder and inflate a new view, you never actually store the viewHolder in the Views tag, so when you scroll and get an exisitng view, view.gettag() returns null, and later when you try and use the ViewHolder you get the Null Pointer Exception. You need to add the calls to setTag().