获取时间在某一个区间内

   //获取当前时间

    NSDate*today = [NSDatedate];

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

    // 时间格式,建议大写    HH 使用 24 小时制；hh 12小时制

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

    NSString* todayStr=[dateFormatstringFromDate:today];//将日期转换成字符串

    today=[ dateFormatdateFromString:todayStr];

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

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

//    NSDate *startDate = [dateFormatter dateFromString:@"2017-07-26"];

    NSDate*startDate = today;

    NSDate*endDate = [dateFormatterdateFromString:@"2019-04-30"];

    //利用NSCalendar比较日期的差异

    NSCalendar *calendar = [NSCalendar currentCalendar];

    NSCalendarUnit unit = NSCalendarUnitDay;//只比较天数差异

    //比较的结果是NSDateComponents类对象

    NSDateComponents*delta = [calendarcomponents:unitfromDate:startDatetoDate:endDateoptions:0];

    NSLog(@"%ld",delta.day);