iOS 计算两个NSDate间间隔天数

+(NSInteger)getDaysFrom:(NSDate *)serverDate To:(NSDate *)endDate
{
NSCalendar *gregorian = [[NSCalendar alloc]
initWithCalendarIdentifier:NSCalendarIdentifierGregorian];

[gregorian setFirstWeekday:2];

//去掉时分秒信息
NSDate *fromDate;
NSDate *toDate;
[gregorian rangeOfUnit:NSCalendarUnitDay startDate:&fromDate interval:NULL forDate:serverDate];
[gregorian rangeOfUnit:NSCalendarUnitDay startDate:&toDate interval:NULL forDate:endDate];
NSDateComponents *dayComponents = [gregorian components:NSCalendarUnitDay fromDate:fromDate toDate:toDate options:0];

return dayComponents.day;

}