iOS怎样通过这样的JSON数据，实现上下拉刷新加载更多

{
"count": 87,
"next": " http://127.0.0.1:5000/api/v1.0/posts/?page=2 ",
"posts": [
{
"author": " http://127.0.0.1:5000/api/v1.0/users/2 ",
"body": "\u66f4\u597d\u6591\u6591\u9a73\u9a73\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d\u4e0d",
"body_html": null,
"body_title": null,
"comment_count": 0,
"comments": " http://127.0.0.1:5000/api/v1.0/posts/1/comments/ ",
"id": 1,
"timestamp": "Wed, 24 Jun 2015 06:40:03 GMT",
"url": " http://127.0.0.1:5000/api/v1.0/posts/1 "
},
{
"author": " http://127.0.0.1:5000/api/v1.0/users/2 ",
"body": "\u770b\u770b\u770b\u770b\u5361\u5361\u5361\u5361\u9760\u9760\u9760\u9760\u9760\u9760\u9760",
"body_html": null,
"body_title": null,
"comment_count": 0,
"comments": " http://127.0.0.1:5000/api/v1.0/posts/2/comments/ ",
"id": 2,
"timestamp": "Wed, 24 Jun 2015 06:40:31 GMT",
"url": " http://127.0.0.1:5000/api/v1.0/posts/2 "
},
{
"author": " http://127.0.0.1:5000/api/v1.0/users/2 ",
"body": "uuuuuuuuuuuuuuuuuuu\u6de1\u6de1\u7684\u6de1\u6de1\u7684\u6de1\u6de1\u7684\u6de1\u6de1\u7684\u6de1\u6de1\u7684\u6de1\u6de1\u7684\u6de1\u6de1\u7684",
"body_html": null,
"body_title": null,
"comment_count": 0,
"comments": " http://127.0.0.1:5000/api/v1.0/posts/3/comments/ ",
"id": 3,
"timestamp": "Wed, 24 Jun 2015 06:40:44 GMT",
"url": " http://127.0.0.1:5000/api/v1.0/posts/3 "
}
],
"prev": null
}