https://cubegao.com/tags/nscache/ Recent content in NSCache on cubegao Hugo zh-CN Mon, 11 Nov 2019 20:13:00 +0800 https://cubegao.com/post/2019-11-11-nscache/ Mon, 11 Nov 2019 20:13:00 +0800 https://cubegao.com/post/2019-11-11-nscache/ <p>第一次见到<code>NSCache</code>，是在<code>SDWebImage</code>中。<code>SDWebImage</code>的内存缓存机制就是通过<code>NSCache</code>完成的。所以可能你不太了解这个类，但是其实一直在使用它。</p> <h3 id="为什么要使用nscache">为什么要使用NSCache？</h3> <p>我们通常用缓存来临时存储短时间使用但创建昂贵的对象。重用这些对象可以优化性能，因为它们的值不需要重新计算。另外一方面，这些对象对于程序来说不是紧要的，在内存紧张时会被丢弃。如果对象被丢弃了，则下次使用时需要重新计算。</p> <p><code>NSCache</code>是一个可变的集合，主要用来存储<code>key-value</code>对。它有着和<code>NSMutableDictionary</code>类似的API。实际上，<code>NSCache</code>就像是一个会自动移除对象来释放内存的<code>NSMutableDictionary</code>。</p> <div class="goat svg-container "> <svg xmlns="http://www.w3.org/2000/svg" font-family="Menlo,Lucida Console,monospace" viewBox="0 0 496 89" > <g transform='translate(8,16)'> <path d='M 0,0 L 8,0' fill='none' stroke='currentColor'></path> <path d='M 0,16 L 8,16' fill='none' 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