title: Null pointer Exception when using view holder in list view adapter
body: <p>I tried to implement view holder in my getView() method,however,it crashed and shows all those views in view holder is null,why,here is my code.</p>
  
  <pre><code>        if(view==null){
              viewHolder=new ViewHolder();
              view=inflater.inflate(R.layout.find_new_thing_item,null);
              viewHolder.progressBar=(ProgressBar)view.findViewById(R.id.find_new_thing_item_progress_bar);
              viewHolder.mainPictureImageView=(ImageView)view.findViewById(R.id.find_new_thing_item_main_image);
              viewHolder.userIconImageView=(ImageView)view.findViewById(R.id.find_new_thing_item_user_icon);
              viewHolder.thingsNameTextView=(TextView)view.findViewById(R.id.find_new_thing_item_name);
              viewHolder.priceTextView=(TextView)view.findViewById(R.id.find_new_thing_item_price);
              viewHolder.userNameTextView=(TextView)view.findViewById(R.id.find_new_thing_item_user_name);
              viewHolder.userCommentTextView=(TextView)view.findViewById(R.id.find_new_thing_item_user_comment);
              viewHolder. numberOfLikesTextView=(TextView)view.findViewById(R.id.find_new_thing_item_number_of_likes);
              viewHolder.numberOfAddToDouListTextView=(TextView)view.findViewById(R.id.find_new_thing_item_number_of_add_to_dou_list);
              viewHolder.numberOfReplyTextView=(TextView)view.findViewById(R.id.find_new_thing_item_number_of_reply);
              view.setTag(viewHolder);
          }else {
              viewHolder=(ViewHolder)view.getTag();
          }
  
  
          new DownloadItemImage().execute(thingsItemArrayList.get(i-1).getMainPicture());
          new DownloadUserIcon().execute(thingsItemArrayList.get(i-1).getUserIcon());
          viewHolder.thingsNameTextView.setText(thingsItemArrayList.get(i - 1).getThingsName());
          viewHolder.priceTextView.setText(thingsItemArrayList.get(i-1).getPrice());
          viewHolder.userNameTextView.setText(thingsItemArrayList.get(i-1).getUserName());
          viewHolder.userCommentTextView.setText(thingsItemArrayList.get(i-1).getUserComment());
          viewHolder.numberOfLikesTextView.setText(thingsItemArrayList.get(i-1).getNumberOfLikes());
          viewHolder.numberOfAddToDouListTextView.setText(thingsItemArrayList.get(i-1).getNumberOfAddToDouList());
          if(thingsItemArrayList.get(i-1).getNumberOfReply().indexOf("评论")&gt;=0){
              viewHolder.numberOfReplyTextView.setText(thingsItemArrayList.get(i-1).getNumberOfReply());
          }else{
              viewHolder.numberOfReplyTextView.setText("评论 0");
          }
  
          return view;
  </code></pre>