这里记录一下iOS中日期比较的方法
NSDate * now = [NSDate date];
NSDate * beforetime = [now dateByAddingTimeInterval:-60];
NSTimeInterval timeBetween = [now timeIntervalSinceDate:beforetime];
NSLog(@"%f",timeBetween);原文：http://blog.csdn.net/qqmcy/article/details/42173147