【iOS】得到当前年、月、周的第一天和最后一天

在写一个记账软件，其中有个统计功能。比如，统计某月的支出，需要知道某天所在的月的第一天和最后一天，以便从数据库中根据时间取数据。

话不多说，上代码：

//

//  EBDate.h

//  ChargeMoney

//

//  Created by eagle on 15-3-24.

//  Copyright (c) 2015年 EagleB. All rights reserved.

//

#import <Foundation/Foundation.h>

@interface EBDate : NSObject

/**

 *  得到这个周的第一天和最后一天

 */

+(NSArray *)getFirstAndLastDayOfThisWeek;

/**

 *  得到这个月的第一天和最后一天

 */

+(NSArray *)getFirstAndLastDayOfThisMonth;

/**

 *  得到今年的第一天和最后一天

 */

+(NSArray *)getFirstAndLastDayOfThisYear;

@end

//

//  EBDate.m

//  ChargeMoney

//

//  Created by eagle on 15-3-24.

//  Copyright (c) 2015年 EagleB. All rights reserved.

//

#import "EBDate.h"

@implementation EBDate

+(NSArray *)getFirstAndLastDayOfThisWeek

{

    NSCalendar *calendar = [NSCalendar currentCalendar];

    NSDateComponents *dateComponents = [calendar components:NSWeekdayCalendarUnit | NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit fromDate:[NSDate date]];

    NSInteger weekday = [dateComponents weekday];   //第几天(从sunday开始)

    NSInteger firstDiff,lastDiff;

    if (weekday == ) {

        firstDiff = -;

        lastDiff = ;

    }else {

        firstDiff =  - weekday + ;

        lastDiff =  - weekday;

    }

    NSInteger day = [dateComponents day];

    NSDateComponents *firstComponents = [calendar components:NSWeekdayCalendarUnit | NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit fromDate:[NSDate date]];

    [firstComponents setDay:day+firstDiff];

    NSDate *firstDay = [calendar dateFromComponents:firstComponents];

    NSDateComponents *lastComponents = [calendar components:NSWeekdayCalendarUnit | NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit fromDate:[NSDate date]];

    [lastComponents setDay:day+lastDiff];

    NSDate *lastDay = [calendar dateFromComponents:lastComponents];

    return [NSArray arrayWithObjects:firstDay,lastDay, nil];

}

+(NSArray *)getFirstAndLastDayOfThisMonth

{

    NSCalendar *calendar = [NSCalendar currentCalendar];

    NSDate *firstDay;

    [calendar rangeOfUnit:NSMonthCalendarUnit startDate:&firstDay interval:nil forDate:[NSDate date]];

    NSDateComponents *lastDateComponents = [calendar components:NSMonthCalendarUnit | NSYearCalendarUnit |NSDayCalendarUnit fromDate:firstDay];

    NSUInteger dayNumberOfMonth = [calendar rangeOfUnit:NSDayCalendarUnit inUnit:NSMonthCalendarUnit forDate:[NSDate date]].length;

    NSInteger day = [lastDateComponents day];

    [lastDateComponents setDay:day+dayNumberOfMonth-];

    NSDate *lastDay = [calendar dateFromComponents:lastDateComponents];

    return [NSArray arrayWithObjects:firstDay,lastDay, nil];

}

+(NSArray *)getFirstAndLastDayOfThisYear

{

    //通过2月天数的改变，来确定全年天数

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

    [formatter setTimeZone:[NSTimeZone systemTimeZone]];

    [formatter setDateFormat:@"yyyy"];

    NSString *dateStr = [formatter stringFromDate:[NSDate date]];

    dateStr = [dateStr stringByAppendingString:@"-02-14"];

    [formatter setDateFormat:@"yyyy-MM-dd"];

    NSDate *aDayOfFebruary = [formatter dateFromString:dateStr];

    NSCalendar *calendar = [NSCalendar currentCalendar];

    NSDate *firstDay;

    [calendar rangeOfUnit:NSYearCalendarUnit startDate:&firstDay interval:nil forDate:[NSDate date]];

    NSDateComponents *lastDateComponents = [calendar components:NSMonthCalendarUnit | NSYearCalendarUnit | NSDayCalendarUnit fromDate:firstDay];

    NSUInteger dayNumberOfFebruary = [calendar rangeOfUnit:NSDayCalendarUnit inUnit:NSMonthCalendarUnit forDate:aDayOfFebruary].length;

    NSInteger day = [lastDateComponents day];

    [lastDateComponents setDay:day++dayNumberOfFebruary-];

    NSDate *lastDay = [calendar dateFromComponents:lastDateComponents];

    return [NSArray arrayWithObjects:firstDay,lastDay, nil];

}

@end

注意频繁创建Canlendar，会严重消耗系统性能，该文章的方法仅提供一个参考。

感谢这篇文章:http://my.oschina.net/yongbin45/blog/156181#OSC_h4_7

--------------------------------------

更新：

上边的方法有点笨了，贴上最新的代码。可能过段时间看，这方法又笨了。不得不说，底层的API提供的功能越来强大，你要写的越来越简单。

 /**

  *  month: range from 1 to 12

  **/

 + (NSArray<NSDate *> *)getFirstAndLastDayOfMonth:(NSInteger)month inYear:(NSInteger)year {

     NSCalendar *calendar = [NSCalendar currentCalendar];

     NSDate *date = [self getDateWithMonth:month year:year];

     NSDate *firstDay;

     NSTimeInterval interval;

     [calendar rangeOfUnit:NSCalendarUnitMonth startDate:&firstDay interval:&interval forDate:date];

     NSDateComponents *lastDateComponents = [calendar components:NSCalendarUnitMonth | NSCalendarUnitYear |NSCalendarUnitDay fromDate:firstDay];

     NSUInteger dayNumberOfMonth = [calendar rangeOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitMonth forDate:date].length;

     NSInteger day = [lastDateComponents day];

     [lastDateComponents setDay:day + dayNumberOfMonth];

     lastDateComponents.nanosecond = lastDateComponents.nanosecond - ;

     NSDate *lastDay = [calendar dateFromComponents:lastDateComponents];

     return [NSArray arrayWithObjects:firstDay,lastDay, nil];

 }

 + (NSArray<NSDate *> *)getFirstAndLastDayOfYear:(NSInteger)year {

     NSDate *date = [self getDateWithYear:year];

     NSCalendar *calendar = [NSCalendar currentCalendar];

     NSDate *firstDay;

     [calendar rangeOfUnit:NSCalendarUnitYear startDate:&firstDay interval:nil forDate:date];

     NSDateComponents *lastDateComponents = [calendar components:NSCalendarUnitMonth | NSCalendarUnitYear | NSCalendarUnitDay fromDate:firstDay];

     NSUInteger dayNumberOfYear = [calendar rangeOfUnit:NSCalendarUnitDay inUnit:NSCalendarUnitYear forDate:date].length;

     NSInteger day = [lastDateComponents day];

     [lastDateComponents setDay:day + dayNumberOfYear];

     lastDateComponents.nanosecond = lastDateComponents.nanosecond - ;

     NSDate *lastDay = [calendar dateFromComponents:lastDateComponents];

     return [NSArray arrayWithObjects:firstDay,lastDay, nil];

 }

 + (NSDate *)getDateWithMonth:(NSInteger)month year:(NSInteger)year {

     NSDateComponents *dateComponents = [[NSDateComponents alloc] init];

     dateComponents.year = year;

     dateComponents.month = month;

     NSCalendar *calendar = [NSCalendar currentCalendar];

     NSDate *date = [calendar dateFromComponents:dateComponents];

     return date;

 }

 + (NSDate *)getDateWithYear:(NSInteger)year {

     NSDateComponents *dateComponents = [[NSDateComponents alloc] init];

     dateComponents.year = year;

     NSCalendar *calendar = [NSCalendar currentCalendar];

     NSDate *date = [calendar dateFromComponents:dateComponents];

     return date;

 }

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【iOS】得到当前年、月、周的第一天和最后一天

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