计算一年中所有周的第一天和最后一天

准备

在看代码之前你可能需要先了解以下知识

• NSDate、NSCalendar和NSDateComponents

• NSCalendar使用详解

代码

  - (void)weeksWithDateComponents:(NSDateComponents *)fromComp
              toDateComponents:(NSDateComponents *)toComp{
    //获取公历日历
    NSCalendar *calendar = [NSCalendar calendarWithIdentifier:NSCalendarIdentifierGregorian];
    //一年中的天数或一年已过的天数
    NSInteger daysOfYear = 0;
    if (toComp) {//计算已过的天数
        daysOfYear = [calendar ordinalityOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitYear forDate:[calendar dateFromComponents:toComp]];
    }else{//计算一年的天数
//        daysOfYear = [calendar rangeOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitYear forDate:[calendar dateFromComponents:fromComp]].length;//在9.3系统里始终是31天
        /*fixed 9.3 bug*/
        for (NSInteger i = 1; i <= 12; i++) {
            fromComp.month = i;
            fromComp.day = 1;
            NSDate *date = [calendar dateFromComponents:fromComp];
            daysOfYear += [calendar rangeOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitMonth forDate:date].length;
        }
    }
    //月份移动至1月
    fromComp.month = 1;
    //记录当前第几周
    NSInteger weekOfYear = 0;
    //遍历每一天
    for (NSInteger i = 1; i <= daysOfYear; i++) {
        @autoreleasepool {
            //移至当前天
            fromComp.day = i;
            NSDate *idate = [calendar dateFromComponents:fromComp];
            NSDateComponents *comp = [calendar components:kCFCalendarUnitDay|kCFCalendarUnitWeekday|kCFCalendarUnitMonth fromDate:idate];
            //星期一开始算周
            if (comp.weekday == 2) {
                weekOfYear += 1;
                fromComp.day = MIN(i+6,daysOfYear);
                NSDate *fdate = [calendar dateFromComponents:fromComp];
                NSString *reslut = [NSString stringWithFormat:@"第%zd周 (%zd月%zd日-%zd月%zd日)",weekOfYear,
                                    [calendar ordinalityOfUnit:NSCalendarUnitMonth inUnit:NSCalendarUnitYear forDate:fdate],
                                    [calendar ordinalityOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitMonth forDate:fdate],
                                    [calendar ordinalityOfUnit:NSCalendarUnitMonth inUnit:NSCalendarUnitYear forDate:idate],
                                    [calendar ordinalityOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitMonth forDate:idate]];
                NSLog(@"%@",reslut);
            }
        }
    }
}

使用

    NSDateComponents * fComp = [[NSCalendar currentCalendar] components:NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay fromDate:[NSDate date]];
    fComp.month = 1;
    fComp.day = 1;
    NSDateComponents * tComp = [[NSCalendar currentCalendar] components:NSCalendarUnitYear|NSCalendarUnitMonth|NSCalendarUnitDay fromDate:[NSDate date]];
    [self weeksWithDateComponents:fComp toDateComponents:tComp];