计算时间

NSDate+MJ.h

#import <Foundation/Foundation.h>

@interface NSDate (MJ)
/**
 *  是否为今天
 */
- (BOOL)isToday;
/**
 *  是否为昨天
 */
- (BOOL)isYesterday;
/**
 *  是否为今年
 */
- (BOOL)isThisYear;

/**
 *  返回一个只有年月日的时间
 */
- (NSDate *)dateWithYMD;

/**
 *  获得与当前时间的差距
 */
- (NSDateComponents *)deltaWithNow;
@end

NSDate+MJ.m

//
//  NSDate+MJ.m
//  ItcastWeibo
//
//  Created by apple on 14-5-9.
//  Copyright (c) 2014年 itcast. All rights reserved.
//

#import "NSDate+MJ.h"

@implementation NSDate (MJ)
/**
 *  是否为今天
 */
- (BOOL)isToday
{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    int unit = NSCalendarUnitDay | NSCalendarUnitMonth |  NSCalendarUnitYear;
    
    // 1.获得当前时间的年月日
    NSDateComponents *nowCmps = [calendar components:unit fromDate:[NSDate date]];
    
    // 2.获得self的年月日
    NSDateComponents *selfCmps = [calendar components:unit fromDate:self];
    return
    (selfCmps.year == nowCmps.year) &&
    (selfCmps.month == nowCmps.month) &&
    (selfCmps.day == nowCmps.day);
}

/**
 *  是否为昨天
 */
- (BOOL)isYesterday
{
    // 2014-05-01
    NSDate *nowDate = [[NSDate date] dateWithYMD];
    
    // 2014-04-30
    NSDate *selfDate = [self dateWithYMD];
    
    // 获得nowDate和selfDate的差距
    NSCalendar *calendar = [NSCalendar currentCalendar];
    NSDateComponents *cmps = [calendar components:NSCalendarUnitDay fromDate:selfDate toDate:nowDate options:0];
    return cmps.day == 1;
}

- (NSDate *)dateWithYMD
{
    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
    fmt.dateFormat = @"yyyy-MM-dd";
    NSString *selfStr = [fmt stringFromDate:self];
    return [fmt dateFromString:selfStr];
}

/**
 *  是否为今年
 */
- (BOOL)isThisYear
{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    int unit = NSCalendarUnitYear;
    
    // 1.获得当前时间的年月日
    NSDateComponents *nowCmps = [calendar components:unit fromDate:[NSDate date]];
    
    // 2.获得self的年月日
    NSDateComponents *selfCmps = [calendar components:unit fromDate:self];
    
    return nowCmps.year == selfCmps.year;
}

- (NSDateComponents *)deltaWithNow
{
    NSCalendar *calendar = [NSCalendar currentCalendar];
    int unit = NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
    return [calendar components:unit fromDate:self toDate:[NSDate date] options:0];
}
@end

// 创建格式化类
    NSDateFormatter *fmt = [[NSDateFormatter alloc] init];
    // 设置格式      _created_at = @"Mon Jul 14 16:13:07 +0800 2014";
    fmt.dateFormat = @"EEE MMM dd HH:mm:ss Z yyyy";
    
#warning 真机调试(真机显示时间，要写上这句话)
    fmt.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];
    // 获得发微博的具体时间
    NSDate *createDate = [fmt dateFromString:_created_at];
    
    // 判断是否为今年
    if (!createDate.isThisYear) {
        fmt.dateFormat = @"yyyy-MM-dd";
        return [fmt stringFromDate:createDate];
    }
    
    if (!createDate.isToday && !createDate.isYesterday) { // 不是今天，也不是昨天
            fmt.dateFormat = @"MM-dd HH:mm";
            return [fmt stringFromDate:createDate];
    }
    if (!createDate.isToday) {
        fmt.dateFormat = @"昨天 HH:mm";
        return [fmt stringFromDate:createDate];
    }
    NSDateComponents *cmps = [createDate deltaWithNow];
    
    if (!cmps.hour >= 1 && !cmps.minute >= 1) {
         return @"刚刚";
    }
    
    if (!cmps.hour >= 1) {
        return [NSString stringWithFormat:@"%d分钟前", cmps.minute];
    }
    
    return  [NSString stringWithFormat:@"%d小时前", cmps.hour];