首先，获得两个比较的日期
//创建时间格式
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSDate *fromDate = [dateFormatter dateFromString:@"2017-01-09 12:02:03"];
NSDate *toDate = [NSDate date];
比较两个日期是否为同一天：
//判断是否为同一天
- (BOOL)isSameDay:(NSDate*)date1 date2:(NSDate*)date2
{
NSCalendar* calendar = [NSCalendar currentCalendar];
unsigned unitFlags = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay;
NSDateComponents* comp1 = [calendar components:unitFlags fromDate:date1];
NSDateComponents* comp2 = [calendar components:unitFlags fromDate:date2];
return [comp1 day] == [comp2 day] &&
[comp1 month] == [comp2 month] &&
[comp1 year] == [comp2 year];
}
相隔多少天
//NSCalendarIdentifierGregorian 公历
NSCalendar *gregorian = [[NSCalendar alloc]
initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
//设定每周的第一天从星期几开始，比如:如需设定从星期日开始，则value传入1;如需设定从星期一开始，则value传入2
[gregorian setFirstWeekday:2];
NSDateComponents *dayComponents = [gregorian components:NSCalendarUnitDay fromDate:fromDate toDate:toDate options:0];
if (labs(dayComponents.day) >= 1) {
//进行检测更新
}
关于NSDateComponents的讲解，可以查看https://my.oschina.net/yongbin45/blog/156181的介绍
