ios 计算当前时间与某一个时间相隔天数

- (NSInteger)getDifferenceByDate:(NSString *)date {

     //获得当前时间

    NSDate*now = [NSDatedate];

    //实例化一个NSDateFormatter对象

   NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

        //设定时间格式

    [dateFormattersetDateFormat:@"yyyy-MM-dd"];

    NSDate*oldDate = [dateFormatterdateFromString: date];

    NSCalendar *gregorian = [[NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];

    unsignedintunitFlags =NSCalendarUnitDay;

    NSDateComponents*comps = [gregoriancomponents:unitFlagsfromDate:oldDate  toDate:now  options:0];

    return[compsday];

}