当前时间转字符串(date→string)

• Mon Dec 7 11:25:11 2020 → 2020-12-07 11:25:11

- (NSString *)getNowDateFormatString{
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    //格式可自定义;
    //DD为全年的中的第n天,dd为某月中的第n天;
    //HH为24小时时间制,hh为12小时时间制;
    [formatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"];
    
    NSDate   *nowDate = [NSDate date];
    NSString *timeString = [formatter stringFromDate:nowDate];
    
    return   timeString;
}

当前时间转时间戳(date→integer)

• Mon Dec 7 11:52:20 2020 → 1607313140000

- (NSInteger)getNowDateFormatInteger{
    NSDate *datenow = [NSDate date];
    NSInteger timeStamp = [[NSNumber numberWithDouble:[datenow timeIntervalSince1970]] integerValue];
    // iOS默认精度为妙(10位)，通常server定义的精度为毫秒，乘以1000即可;
    NSInteger timeInteger = timeStamp * 1000;
    return   timeInteger;
}

时间戳转字符串(integer→string)

• 1607313140000 → 2020-12-07 11:25:11

- (NSString *)formatTimeWithTimeStamp:(NSInteger)integer{
    //这里以13位时间戳为例,ios默认精度为妙,故除以1000后再转换;
    //如果这里传入的integer有误,则会返回时间起始年"1970";
    NSInteger target = integer / 1000;
    NSDate *date = [[NSDate alloc]initWithTimeIntervalSince1970:target];
    
    //格式化成目标时间格式
    NSDateFormatter *formatter = [[NSDateFormatter alloc]init];
    [formatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"];
    NSString  *timeString  = [formatter stringFromDate:date];
    
    return timeString;
}

格式化统一字符串形式(统一样式，统一成其中的一种)

• 2019/07/26 10:32:18
• 2019-07-26 10:32:18

- (NSString *)dateFormatWithString:(NSString *)string {
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    // 传进来的日期格式
    [formatter setDateFormat:@"YYYY/MM/dd HH:mm:ss"];
    // 先将传进来的字符串日期转换成NSDate
    NSDate *date =[formatter dateFromString:string];
    
    // 目标日期格式
    [formatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"];
    NSString *timeString = [formatter stringFromDate:date ];
    
    return timeString;
}

天数差(与当前时间做比较，相差的天数)

- (NSInteger)daysOfNumberWithString:(NSString *)lastString{
    //这里需要注意传入参数lastString时间格式，要与当前时间格式统一，才可以作比较
    NSInteger days;
    NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
    //这里格式要设置成统一
    [formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    
    NSDate *lastDate = [formatter dateFromString:laststring];
    //调用上述时间格式化方法
    NSString *nowString = [self getNowDateFormatString];
    NSDate   *nowDate = [formatter dateFromString:nowString];
    
    NSTimeInterval time = [nowDate timeIntervalSinceDate:lastDate];
    days = time / (60 * 60 *24);
    
    return days;
}

多少天多少小时多少分钟多少秒(例如朋友圈发布的消息，已经过了多长时间)

- (NSString *)dateTimeDifferenceWithStartTime:(NSString *)startTime endTime:(NSString *)endTime {
    NSDateFormatter *date = [[NSDateFormatter alloc]init];
    [date setDateFormat:@"yyyy-MM-dd-HH:mm:ss"];
    
    NSDate *startDate =[date dateFromString:startTime];
    NSDate *endDdate = [date dateFromString:endTime];
    
    NSCalendar *cal = [NSCalendar currentCalendar];
    unsigned int unitFlags = NSCalendarUnitYear | NSCalendarUnitMonth | NSCalendarUnitDay | NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
    NSDateComponents *dateComponents = [cal components:unitFlags fromDate:startDate toDate:endDdate options:0];
    
    // 天
    NSInteger day = [dateComponents day];
    // 小时
    NSInteger house = [dateComponents hour];
    // 分
    NSInteger minute = [dateComponents minute];
    // 秒
    NSInteger second = [dateComponents second];
    NSString *timeStr;
    if (day != 0) {
        timeStr = [NSString stringWithFormat:@"%zd天%zd小时%zd分%zd秒",day,house,minute,second];
    }
    else if (day==0 && house !=0) {
        timeStr = [NSString stringWithFormat:@"%zd小时%zd分%zd秒",house,minute,second];
    }
    else if (day==0 && house==0 && minute!=0) {
        timeStr = [NSString stringWithFormat:@"%zd分%zd秒",minute,second];
    }
    else{
        timeStr = [NSString stringWithFormat:@"%zd秒",second];
    }
    return timeStr;
}