如何将此转换为Fragment以使用ViewPager？
@Override
public View getView(int position, View convertView, ViewGroup parent) {
final ViewHolder holder;
View view = convertView;
if (view == null) {
view = getLayoutInflater().inflate(R.layout.item_grid_image, parent, false);
holder = new ViewHolder();
assert view != null;
holder.imageView = (ImageView) view.findViewById(R.id.image);
holder.progressBar = (ProgressBar)view.findViewById(R.id.progress);
view.setTag(holder);
// ......
}
}