这里写的是给一个日期计算出 这个日期所在的一周是几号到几号。吧日期换成今天日期也就是本周是几号到几号。考虑到有跨月，跨年等等的问题，直接就根据秒数来计算比较不会错。在者考虑到过内外的一周是不一样的。国内周一是一周的第一天也就是一周是周一到周日，国外是周日的一周的第一天也就是周日到下周的周六。

#import "ViewController.h"@interface ViewController ()
{UITextField * _textField;
}@end@implementation ViewController- (void)viewDidLoad {[super viewDidLoad];// 2016.8.8 星期一// 2016.8.9 星期二// 2016.8.11 星期4// 2016.8.14 星期日UIButton * btn = [[UIButton alloc]initWithFrame:CGRectMake((self.view.frame.size.width-80)/2.0, 100, 80, 30)];btn.backgroundColor = [UIColor orangeColor];btn.tag = 1001;[btn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];[btn setTitle:@"国内计算" forState:UIControlStateNormal];[btn addTarget:self action:@selector(btnAction:) forControlEvents:UIControlEventTouchUpInside];[self.view addSubview:btn];UIButton * btn2 = [[UIButton alloc]initWithFrame:CGRectMake((self.view.frame.size.width-80)/2.0, 140, 80, 30)];btn2.backgroundColor = [UIColor orangeColor];[btn2 setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];[btn2 setTitle:@"国外计算" forState:UIControlStateNormal];btn2.tag = 1000;[btn2 addTarget:self action:@selector(btnAction:) forControlEvents:UIControlEventTouchUpInside];[self.view addSubview:btn2];_textField = [[UITextField alloc]initWithFrame:CGRectMake((self.view.frame.size.width-150)/2.0, CGRectGetMinY(btn.frame)-50, 150, 30)];_textField.backgroundColor = [UIColor yellowColor];[self.view addSubview:_textField];}- (void)btnAction:(UIButton*)sender
{if (sender.tag == 1000) {NSDictionary * dic = [ViewController weekfirstAndLastDay:_textField.text Formater:@"yyyy.MM.dd" Foreign:YES];NSLog(@"%@",dic);}else{NSDictionary * dic = [ViewController weekfirstAndLastDay:_textField.text Formater:@"yyyy.MM.dd" Foreign:NO];NSLog(@"%@",dic);}
}+(NSDictionary *)weekfirstAndLastDay:(NSString*)dateStr Formater:(NSString*)formater Foreign:(BOOL)foreign
{NSDateFormatter *formatter = [[NSDateFormatter alloc] init];[formatter setDateFormat:formater];NSDate * date =[formatter dateFromString:dateStr];NSArray * foreginDateArr = @[@"星期日",@"星期一",@"星期二",@"星期三",@"星期四",@"星期五",@"星期六"];NSArray * chineseDateArr = @[@"星期一",@"星期二",@"星期三",@"星期四",@"星期五",@"星期六",@"星期日"];NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];[dateFormatter setDateFormat:@"YYYY.MM.dd"];NSCalendar *calendar = [NSCalendar currentCalendar];NSDateComponents *comp = [calendar components:kCFCalendarUnitYear|kCFCalendarUnitMonth|kCFCalendarUnitDay|kCFCalendarUnitWeekday|kCFCalendarUnitDay fromDate:date];NSInteger foreginWeekDay = [comp weekday];NSString * foreginDateStr = foreginDateArr[foreginWeekDay-1];NSInteger chineseWeekDay = 0;if (foreign) {chineseWeekDay = foreginWeekDay;}else{for (int i = 0; i < foreginDateArr.count; i++) {if ([foreginDateStr isEqualToString:chineseDateArr[i]]) {chineseWeekDay = i+1;break;}}}NSInteger gapDate = 7- chineseWeekDay;//把时间转化成秒NSTimeInterval dateStamp = [date timeIntervalSince1970];//把秒转化成时间NSTimeInterval beginStamp = dateStamp - 24*60*60*(chineseWeekDay-1);NSTimeInterval endStamp = dateStamp + 24*60*60*gapDate;NSDate * begin = [NSDate dateWithTimeIntervalSince1970:beginStamp];NSDate * end = [NSDate dateWithTimeIntervalSince1970:endStamp];NSString * beginStr = [dateFormatter stringFromDate:begin];NSString * endStr = [dateFormatter stringFromDate:end];NSDictionary * dic = @{@"begin":beginStr,@"end":endStr,@"now":dateStr};return dic;
}

思路就是算出这个日期是属于一周的第几天，然后在相应的减去秒数，加上秒数算出一周是从几号到几号。

分别计算了国内外