ListView 效率优化

private class callsmsAdapter extends BaseAdapter {

		@Override
		public Object getItem(int position) {
			return null;
		}

		@Override
		public long getItemId(int position) {
			return 0;
		}

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

		@Override
		public View getView(int position, View convertView, ViewGroup parent) {
			View view;
			ViewHolder holder;
			if (convertView == null) {
				view = View.inflate(getApplicationContext(), R.layout.item_call_sms_safe, null);
				holder = new ViewHolder();
				holder.tv_number = (TextView) view.findViewById(R.id.tv_black_number);
				holder.tv_mode = (TextView) view.findViewById(R.id.tv_black_mode);
				view.setTag(holder);
			} else {
				view = convertView;
				holder= (ViewHolder) view.getTag();
			}
			BlackNumberInfo info = list.get(position);
			holder.tv_number.setText(info.getNumber());
			switch (info.getMode() + "") {
			case 1 + "":
				holder.tv_mode.setText("电话拦截");
				break;
			case 2 + "":
				holder.tv_mode.setText("短信拦截");
				break;
			default:
				holder.tv_mode.setText("全部拦截");
				break;
			}
			return view;
		}
	}

	static class ViewHolder {
		TextView tv_number;
		TextView tv_mode;
	}