NSCalendar 功能很強(qiáng)大，多次調(diào)用時(shí)需要考慮性能問題，但必要的使用會(huì)在日期計(jì)算時(shí)事半功倍。

計(jì)算周次所在日期范圍

-(NSString*)timeConversionYear:(NSInteger)year WeakOfYear:(NSInteger)weekofYear
{
    //周次的范圍日期  幾月幾日 - 幾月幾日
    NSString *weekDate = @"";
    //時(shí)間軸 取每一年的六月一號(hào) 沒有特別的含義
    NSString *timeAxis = [NSString stringWithFormat:@"%ld-06-01 12:00:00",(long)year];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    //獲得了時(shí)間軸
    NSDate *date = [dateFormatter dateFromString:timeAxis];
    
    //日歷類 提供大部分的時(shí)間計(jì)算接口
    NSCalendar *calendar = [NSCalendar currentCalendar];
    /**這兩個(gè)參數(shù)的設(shè)置影響著周次的個(gè)數(shù)和劃分*****************/
    [calendar setFirstWeekday:2]; //設(shè)置每周的開始是星期一
    [calendar setMinimumDaysInFirstWeek:7]; //設(shè)置一周至少需要幾天
    /****************/
    //一個(gè)封裝了具體年月日、時(shí)秒分、周、季度等的類
    NSDateComponents *comps = [calendar components:(NSCalendarUnitWeekOfYear | NSCalendarUnitWeekday | NSCalendarUnitWeekdayOrdinal | NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay)
                                          fromDate:date];
    
    //時(shí)間軸是當(dāng)前年的第幾周
    NSInteger todayIsWeek = [comps weekOfYear];
    //第幾周的字符串格式
    //NSString *todayIsWeekStr = [NSString stringWithFormat:@"%ld",(long)todayIsWeek];
    
    //獲取時(shí)間軸是星期幾 1(星期天) 2(星期一) 3(星期二) 4(星期三) 5(星期四) 6(星期五) 7(星期六)
    NSInteger todayIsWeekDay = [comps weekday];
    
    //得到時(shí)間軸是幾號(hào)
    // NSInteger todayIsDay = [comps day];
    // 計(jì)算當(dāng)前日期和這周的星期一和星期天差的天數(shù)
    //firstDiff 星期一相差天數(shù) 、 lastDiff 星期天相差天數(shù)
    long firstDiff,lastDiff;
    if (todayIsWeekDay == 1) {
        firstDiff = -6;
        lastDiff = 0;
    }else
    {
        firstDiff = [calendar firstWeekday] - todayIsWeekDay;
        lastDiff = 8 - todayIsWeekDay;
    }
    
    NSDate *firstDayOfWeek= [NSDate dateWithTimeInterval:24*60*60*firstDiff sinceDate:date];
    NSDate *lastDayOfWeek= [NSDate dateWithTimeInterval:24*60*60*lastDiff sinceDate:date];
    
    long weekdifference = weekofYear - todayIsWeek;
    
    firstDayOfWeek= [NSDate dateWithTimeInterval:24*60*60*7*weekdifference sinceDate:firstDayOfWeek];
    lastDayOfWeek= [NSDate dateWithTimeInterval:24*60*60*7*weekdifference sinceDate:lastDayOfWeek];
    // NSLog(@"星期一的日期 %@",[dateFormatter stringFromDate:firstDayOfWeek]);
    // NSLog(@"星期天的日期 %@",[dateFormatter stringFromDate:lastDayOfWeek]);
    
    NSDateComponents *firstDayOfWeekcomps = [calendar components:(NSCalendarUnitWeekOfYear | NSCalendarUnitWeekday | NSCalendarUnitWeekdayOrdinal | NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay)
                                                        fromDate:firstDayOfWeek];
    NSDateComponents *lastDayOfWeekcomps = [calendar components:(NSCalendarUnitWeekOfYear | NSCalendarUnitWeekday | NSCalendarUnitWeekdayOrdinal | NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay)
                                                       fromDate:lastDayOfWeek];
    
    NSInteger startMonth = [firstDayOfWeekcomps month];
    NSInteger startDay = [firstDayOfWeekcomps day];
    
    NSInteger endmonth = [lastDayOfWeekcomps month];
    NSInteger endday = [lastDayOfWeekcomps day];
    weekDate = [NSString stringWithFormat:@"%ld.%ld.%ld-%ld.%ld.%ld",year,(long)startMonth,(long)startDay,year,(long)endmonth,(long)endday];
    return weekDate;
}

計(jì)算年有多少周

+(NSInteger)weeksInOneYear:(NSInteger)year
{
    NSString *timeAxis = [NSString stringWithFormat:@"%ld-12-31 12:00:00",(long)year];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    //獲得了時(shí)間軸
    NSDate *date = [dateFormatter dateFromString:timeAxis];
    //日歷類 提供大部分的時(shí)間計(jì)算接口
    NSCalendar *calendar = [NSCalendar currentCalendar];
    [calendar setFirstWeekday:2];
    [calendar setMinimumDaysInFirstWeek:7];
    
    //    NSRange range = [calendar rangeOfUnit:NSCalendarUnitWeekOfYear inUnit:NSCalendarUnitYear forDate:date];
    NSInteger length = [calendar ordinalityOfUnit:NSCalendarUnitWeekOfYear inUnit:NSCalendarUnitYear forDate:date];
    return length;
}