获取某个日期所在周的起始日期

定义全局变量，firstDayOfWeek是开始的日期，lastDayOfWeek是结束的日期：

  NSDate *firstDayOfWeek;
  NSDate *lastDayOfWeek;
  NSCalendar *calendar;
  NSDate *date;

我这边获取的是当前日期：

- (void)getNowTime{
    date = [NSDate date];
    calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    int unitFlags =  NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit |
    NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
    
    NSDateComponents *comps = [calendar components:unitFlags fromDate:date];
    year = [comps year];
    month = [comps month];
    day = [comps day];
    week = [comps weekday];
}

也可以改成其它的日期：

 [comps setMonth:6];
 [comps setDay:1];
 [comps setYear:2017];
 NSDate *weekDate = [calendar dateFromComponents:comps];
int unitFlags =  NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit |
            NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;            
 NSDateComponents *weekComps = [calendar components:unitFlags fromDate:weekDate];

//            [weekComps weekday]  当前日期是周几
//            [weekComps day]      得到几号
[self getWeekDate:weekComps Week:[weekComps weekday] Day:[weekComps day]];

最后直接调用一下方法：

- (void)getWeekDate:(NSDateComponents*)comps1 Week:(NSInteger)weekDay Day:(NSInteger)getDay{
    // 计算当前日期和这周的星期一和星期天差的天数
    long firstDiff,lastDiff;
    if (weekDay == 1){
        firstDiff = -6;
        lastDiff = 0;
    }else{
        firstDiff = [calendar firstWeekday] - weekDay + 1;
        lastDiff = 8 - weekDay;
    }
        [comps1 setDay:getDay+firstDiff];
        firstDayOfWeek = [calendar dateFromComponents:comps1];
        
        [comps1 setDay:getDay+lastDiff];
        lastDayOfWeek = [calendar dateFromComponents:comps1];
        
        NSDateFormatter *formater = [[NSDateFormatter alloc] init];
        [formater setDateFormat:@"MM.dd"];
    
       //起始日期
       NSString *str = [NSString stringWithFormat:@"%@-%@",[formater stringFromDate:firstDayOfWeek],[formater stringFromDate:lastDayOfWeek]];

}

最近写的这个项目的需求是获取一直到当前日期的月日日期、所有周的起始日期和所有的年月，就写了一下：

#import <UIKit/UIKit.h>
@interface BasicViewController : UIViewController
{
    NSMutableArray *MD_DateArray;
    NSMutableArray *Z_DateArray;
    NSMutableArray *YM_DateArray;
}
@end

#import "BasicViewController.h"
#define beginYear 2017 //开始日期

@interface BasicViewController ()
{
    NSCalendar *calendar;
    NSDate *date;
    NSInteger year;
    NSInteger month;
    NSInteger day;
    NSInteger week;
    NSDate *firstDayOfWeek;
    NSDate *lastDayOfWeek;
    NSString *lastDate;
}
@end

@implementation BasicViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    MD_DateArray = [NSMutableArray array];
    Z_DateArray = [NSMutableArray array];
    YM_DateArray = [NSMutableArray array];
    [self reloadData];
}

- (void)viewWillAppear:(BOOL)animated{

    [super viewWillAppear:animated];
    [[UIBarButtonItem appearance]setBackButtonTitlePositionAdjustment:UIOffsetMake(NSIntegerMin, NSIntegerMin) forBarMetrics:UIBarMetricsDefault];
    
    [self.navigationController.navigationBar setTintColor:[UIColor whiteColor]];
}
- (void)reloadData{
    
    [self getNowTime];
    
}

- (void)getNowTime{
    date = [NSDate date];
    calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    int unitFlags =  NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit |
    NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
    
    NSDateComponents *comps = [calendar components:unitFlags fromDate:date];
    year = [comps year];
    month = [comps month];
    day = [comps day];
    week = [comps weekday];
    
    [self getAllMonth:comps];
    [self getAllYear:comps];
}

- (void)getAllMonth:(NSDateComponents*)comps{
   
    for (int i = 1; i<month+1+(year-beginYear)*12; i++) {
        if (i%12 != 0) {
            [comps setMonth:i%12];
        }
//        [comps setMonth:i];
        [comps setDay:1];
        [comps setYear:beginYear+i/12];
        date = [calendar dateFromComponents:comps];
        NSLog(@"date:%@",date);
      NSInteger number = (NSInteger)[[NSCalendar currentCalendar] rangeOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitMonth forDate:date].length;//一个月的天数
        NSLog(@"====================i:%d,number:%ld",i,(long)number);
        if ((beginYear+i/12 == year) && (i == month)) {
            number = day;
        }
        if (i%12 == 0) {
            i = 12;
        }
        NSLog(@"day:%ld",(long)day);
        for (int j = 1; j<number+1; j++) {
        [MD_DateArray addObject:[NSString stringWithFormat:@"%d.%d",i%12,j]];
            [comps setMonth:i];
            [comps setDay:j];
            [comps setYear:beginYear+i/12];
             NSDate *weekDate = [calendar dateFromComponents:comps];
            int unitFlags =  NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit |
            NSHourCalendarUnit | NSMinuteCalendarUnit | NSSecondCalendarUnit;
            
            NSDateComponents *weekComps = [calendar components:unitFlags fromDate:weekDate];

            [self getWeekDate:weekComps Week:[weekComps weekday] Day:[weekComps day]];
        }
    }
   
}

- (void)getAllYear:(NSDateComponents*)comps{
    int mon = 0;
    int yea = 0;
    for (int i = 1; i<month+1+(year-beginYear)*12; i++) {
        mon = i;
        if (i%12 == 0) {
            mon = 12;
        }else{
            mon = i%12;
        }
        if (i<13) {
            yea = 0;
        }else{
            yea = i/12;
        }
        [YM_DateArray addObject:[NSString stringWithFormat:@"%d年%d月",beginYear+yea,mon]];
    }

}

- (void)getWeekDate:(NSDateComponents*)comps1 Week:(NSInteger)weekDay Day:(NSInteger)getDay{
    // 计算当前日期和这周的星期一和星期天差的天数
    long firstDiff,lastDiff;
    if (weekDay == 1){
        firstDiff = -6;
        lastDiff = 0;
    }else{
        firstDiff = [calendar firstWeekday] - weekDay + 1;
        lastDiff = 8 - weekDay;
    }
        [comps1 setDay:getDay+firstDiff];
        firstDayOfWeek = [calendar dateFromComponents:comps1];
        
        [comps1 setDay:getDay+lastDiff];
        lastDayOfWeek = [calendar dateFromComponents:comps1];
        
        NSDateFormatter *formater = [[NSDateFormatter alloc] init];
        [formater setDateFormat:@"MM.dd"];
    
       NSString *str = [NSString stringWithFormat:@"%@-%@",[formater stringFromDate:firstDayOfWeek],[formater stringFromDate:lastDayOfWeek]];
    if ([str isEqualToString:lastDate]) {
        return;
    }else{
        
        [Z_DateArray addObject:[NSString stringWithFormat:@"%@-%@",[formater stringFromDate:firstDayOfWeek],[formater stringFromDate:lastDayOfWeek]]];
         lastDate = str;
    }
//            NSLog(@"Z_DateArray:%@",Z_DateArray);
//    }
}

@end

因为有多个类要使用，所以我直接写在父类里边，我感觉我写的比较麻烦，谁有更简单方法的，希望赐教。