UIKIT_EXTERN NSString *const UIApplicationDidReceiveMemoryWarningNotification;
内存警告能够写在
- (void)didReceiveMemoryWarning
{
}
方法中，可是在通知中实现效率更高，警告的方法运行顺序在通知之后
[[NSNotificationCenter defaultCenter ]addObserver:self selector:@selector(memoryWarning) name:UIApplicationDidReceiveMemoryWarningNotification object:nil];
原文：http://www.cnblogs.com/yxwkf/p/5179391.html