ListView使用ViewHolder极简写法

public static <T extends View> T getAdapterView(View convertView, int id) {
    SparseArray<View> viewHolder = (SparseArray<View>) convertView.getTag();
    if (viewHolder == null) {
        viewHolder = new SparseArray<View>();
        convertView.setTag(viewHolder);
    }
    View childView = viewHolder.get(id);
    if (childView == null) {
        childView = convertView.findViewById(id);
        viewHolder.put(id, childView);
    }
    return (T) childView;
}

//用法
@Override
public View getView(int position, View convertView, ViewGroup parent) {
    if (convertView == null) {
        convertView = LayoutInflater.from(getActivity()).inflate(R.layout.fragment_feed_item, parent, false);
    }

    ImageView thumnailView = getAdapterView(convertView, R.id.video_thumbnail);
    ImageView avatarView =  getAdapterView(convertView, R.id.user_avatar);
    ImageView appIconView = getAdapterView(convertView, R.id.app_icon);

    ...

}