BaseAdapter基本使用

 class PhotoAdapter extends BaseAdapter {


        @Override
        public int getCount() {
            return imagePathList.size();
        }

        @Override
        public Object getItem(int i) {
            return imagePathList.get(i);
        }

        @Override
        public long getItemId(int i) {
            return i;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup viewGroup) {
            //有很多例子中都用到这个holder,理解下??
            ViewHolder holder = null;
            //思考这里为何要判断convertView是否为空  ？？
            if (convertView == null) {
                holder = new ViewHolder();
                convertView = View.inflate(MainActivity.this, R.layout.item_photo, null);
                holder.iv_item_photo = (ImageView) convertView.findViewById(R.id.iv_item_photo);
                convertView.setTag(holder);
            } else {
                holder = (ViewHolder) convertView.getTag();
            }
            Bitmap bitmap = getLoacalBitmap(imagePathList.get(position)); //从本地取图片(在cdcard中获取)  //
            holder.iv_item_photo.setImageBitmap(bitmap);
            return convertView;
        }
    }



    class ViewHolder {
        private ImageView iv_item_photo;

    }