请问如何用NSURLCache实现这个逻辑

1 请求时先判断是否有缓存
2 如果有缓存 先用缓存渲染页面
3 然后接着发送请求最新的数据
4 当数据回来时在用新的数据渲染页面，同时更新缓存
5 如果2没有缓存，就直接发请求渲染

Start by locating the NSURLCache integration and the code that requests and renders the page data. Trace whether cached data is available before each request, then identify the request completion path. Done means cached content renders immediately when present, a fresh request still runs, the newer response replaces the view and cache, and a cache miss renders the response directly.

Written by the indexing model from the issue text.