刚刚看到了一个小知识点，拿出来与大家分享一下，也是做个笔记。
NSURLRequest有缓存策略，是这条属性：
/*! @method cachePolicy @abstract Returns the cache policy of the receiver. @result The cache policy of the receiver. */ @property (readonly) NSURLRequestCachePolicy cachePolicy;
NSURLRequestCachePolicy 是一个枚举
typedef NS_ENUM(NSUInteger, NSURLRequestCachePolicy) { NSURLRequestUseProtocolCachePolicy = 0, NSURLRequestReloadIgnoringLocalCacheData = 1, NSURLRequestReloadIgnoringLocalAndRemoteCacheData = 4, // Unimplemented NSURLRequestReloadIgnoringCacheData = NSURLRequestReloadIgnoringLocalCacheData, NSURLRequestReturnCacheDataElseLoad = 2, NSURLRequestReturnCacheDataDontLoad = 3, NSURLRequestReloadRevalidatingCacheData = 5, // Unimplemented };
有这么几个值，分别是这些意思：
默认缓存策略：NSURLRequestUseProtocolCachePolicy
忽视本地缓存，只加载网络数据：NSURLRequestReloadIgnoringLocalCacheData
先加载本地缓存，没有的情况下网络请求数据：NSURLRequestReturnCacheDataElseLoad
不加载本地缓存，直接请求：NSURLRequestReturnCacheDataDontLoad
原文：http://www.cnblogs.com/FrankieZ/p/5192639.html