Onscrolling，获得的图像在android中消失

Question

public Object instantiateItem(ViewGroup container, int position) {

        // Declare Variables
        TextView txtrank;

        ImageView imgflag;

        inflater = (LayoutInflater) context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        View itemView = inflater.inflate(R.layout.viewpager_item, container,
                false);

        // Locate the TextViews in viewpager_item.xml
        txtrank = (TextView) itemView.findViewById(R.id.rank);


        // Capture position and set to the TextViews
        txtrank.setText(worldpopulationlist.get(position).getImage());


        // Locate the ImageView in viewpager_item.xml
        imgflag = (ImageView) itemView.findViewById(R.id.flag);
        // Capture position and set to the ImageView
//        imgflag.setImageResource(flag[position]);

        String smage= worldpopulationlist.get(position).getImage();
        Uri uri = Uri.parse(worldpopulationlist.get(position).getImage());



        Picasso.with(context)
                .load(uri)
                .into(imgflag);
        // Add viewpager_item.xml to ViewPager
        ((ViewPager) container).addView(itemView);

        return itemView;
    }

此处图片来自parse.com服务器，第一次加载，然后移动到该位置后重新加载。