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;
/**
 *  得到今天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 == 1) {
        firstDiff = -6;
        lastDiff = 0;
    }else {
        firstDiff =  - weekday + 2;
        lastDiff = 8 - 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-1];
    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+337+dayNumberOfFebruary-1];
    NSDate *lastDay = [calendar dateFromComponents:lastDateComponents];
    
    return [NSArray arrayWithObjects:firstDay,lastDay, nil];
}

@end

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