谁能举例说明如何使用 NSCache
缓存字符串?
或者任何人都有一个很好的解释的链接?好像没找到啊。。
最佳答案
您使用它的方式与使用 NSMutableDictionary
的方式相同。不同之处在于,当 NSCache
检测到内存压力过大(即缓存了太多值)时,它会释放其中的一些值以腾出空间。
如果您可以在运行时重新创建这些值(通过从 Internet 下载、进行计算等),那么 NSCache
可能会满足您的需求。如果无法重新创建数据(例如,它是用户输入、时间敏感等),那么您不应该将其存储在 NSCache
中,因为它将在那里被销毁。
例如,不考虑线程安全:
// Your cache should have a lifetime beyond the method or handful of methods
// that use it. For example, you could make it a field of your application
// delegate, or of your view controller, or something like that. Up to you.
NSCache *myCache = ...;
NSAssert(myCache != nil, @"cache object is missing");
// Try to get the existing object out of the cache, if it's there.
Widget *myWidget = [myCache objectForKey: @"Important Widget"];
if (!myWidget) {
// It's not in the cache yet, or has been removed. We have to
// create it. Presumably, creation is an expensive operation,
// which is why we cache the results. If creation is cheap, we
// probably don't need to bother caching it. That's a design
// decision you'll have to make yourself.
myWidget = [[[Widget alloc] initExpensively] autorelease];
// Put it in the cache. It will stay there as long as the OS
// has room for it. It may be removed at any time, however,
// at which point we'll have to create it again on next use.
[myCache setObject: myWidget forKey: @"Important Widget"];
}
// myWidget should exist now either way. Use it here.
if (myWidget) {
[myWidget runOrWhatever];
}
https://stackoverflow.com/questions/5755902/