android – 错误的图像显示在我的ListView行中

@Override
public View getView(int position,View convertView,ViewGroup parent) {
    View v = convertView;
    if (v == null) {

        LayoutInflater vi = (LayoutInflater) getSystemservice(Context.LAYOUT_INFLATER_serviCE);
        v = vi.inflate(R.layout.listrow,null);
    }
    Order o = items.get(position);

    if (o != null) {
        TextView tt = (TextView) v.findViewById(R.id.toptext);
        ImageView thumb = (ImageView) v.findViewById(R.id.icon);

        if (o.getOrderDrawable() != null) {
            thumb.setImageDrawable(o.getOrderDrawable());
        } else {
            tt.setText(o.getOrdertitle());
        }

    }
    return v;
}

问题是滚动时;有时会显示正确的图像,但有时向后/向前滚动时,图像会随机显示,并且与行无关.

图像从网上下载.

我该如何解决这个问题？