Problem with "ViewHolder" class in android

Question

I have a problem when use "ViewHolder" class. I use "ViewHolder" to improve my List display speech. I think the code is ok, but why It throw exception when "setText" with data from "Cursor". My code here:

if(row==null){
   LayoutInflater inflater = LayoutInflater.from(context);   
   row = inflater.inflate(R.layout.sbooks_row, null);
   holder = new ViewHolder();

   holder.id = (TextView)row.findViewById(R.id.id);
   holder.title = (TextView)row.findViewById(R.id.title);
   holder.icon = (ImageView)row.findViewById(R.id.icon);

   row.setTag(holder);
  }
  else
  {
   holder = (ViewHolder)row.getTag();
  }

  holder.title.setText(cursor.getString(cursor.getColumnIndex(SBooksDbAdapter.KEY_TITLE)));
  holder.id.setText(cursor.getString(cursor.getColumnIndex(SBooksDbAdapter.KEY_ROWID)));

Answer 1

You do not say what the exception is. I am going to guess it is a NullPointerException, which means either:

1. You do not have a widget in your row with android:id="@+id/title", or
2. You do not have a column in your result set named SBooksDbAdapter.KEY_TITLE, or
3. Somehow you are creating rows with no holder in its tag