标准时间即(2017-05-05 17:33:09)字符串；

//时间戳 转 标准时间（2017-07-15格式） - wsx注释
+(NSString *)timeStampSwitchStandardTime:(long long)timeStamp{
    NSDate *date = [NSDate dateWithTimeIntervalSince1970:timeStamp];//秒数@"1493976789"转时间    
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"];
    NSString *time = [formatter stringFromDate:date];//时间转标准时间字符串
    NSLog(@"标准时间字符串:%@",time);
    
    return time;
}

打印截图：

秒转标准时间.png

进阶转换，显示多少秒/分/小时/天之前，代码如下:

//时间戳 转 标准时间（2017-07-15格式） - wsx注释
+(NSString *)timeStampSwitchStandardTime:(long long)timeStamp{
    NSDate *nowDate = [NSDate date];
    NSDate *oldDate = [NSDate dateWithTimeIntervalSince1970:timeStamp];//时间戳转Date时间
    // 两个时间戳的间隔   返回的是秒
    NSTimeInterval timeInterval = [nowDate timeIntervalSinceDate:oldDate];
    NSInteger interval = (NSInteger)timeInterval;
    //日期获取 - wsx注释
    NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
    [formatter setDateFormat:@"YYYY-MM-dd"];
    NSString *time;
    if (interval < 60 ) {
        time = [NSString stringWithFormat:@"%ld秒前",(long)interval];
    }else if (interval < 60*60){
        time = [NSString stringWithFormat:@"%ld分前",(long)interval/60];
    }else if (interval < 60*60*24){
        time = [NSString stringWithFormat:@"%ld小时前",(long)interval/3600];
    }else if (interval < 60*60*24*2){
        time = @"昨天";
    }else if (interval < 60*60*24*3){
        time = @"前天";
    }else{
        time = [formatter stringFromDate:oldDate];//时间转标准时间字符串
    }
    NSLog(@"标准时间字符串:%@",time);
    
    return time;
}

标准时间转时间戳：

- (NSString *)obtainTimeStampFromStandardTimeWithStartTime:(NSString *)startTime EndTime:(NSString *)endTime {
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateStyle:NSDateFormatterMediumStyle];
    [dateFormatter setTimeStyle:NSDateFormatterShortStyle];
    [dateFormatter setDateFormat:@"YYYY-MM-dd HH:mm:ss"]; // hh表示:12小时制,HH表示:24小时制
    //设置时区,这个对于时间的处理很重要
    NSTimeZone* timeZone = [NSTimeZone timeZoneWithName:@"Asia/Shanghai"];
    [dateFormatter setTimeZone:timeZone];
    NSString *nowTimeStamp = [NSString stringWithFormat:@"%ld", (long)[[NSDate date] timeIntervalSince1970]];
    // 开始时间转换
    NSDate *startDate = [dateFormatter dateFromString:startTime]; // 将standardTime字符串按dateFormatter转成NSDate
    NSString *startTimeStamp = [NSString stringWithFormat:@"%ld", (long)[startDate timeIntervalSince1970]]; // date与当前时间差8小时  // 得到秒
    // 结束时间转换
    NSDate *endDate = [dateFormatter dateFromString:endTime];
    NSString *endTimeStamp = [NSString stringWithFormat:@"%ld", (long)[endDate timeIntervalSince1970]]; // 得到秒
    // 比较时间差
    if ([[NSDate date] timeIntervalSinceDate:startDate] < 0.0f) {
        return @"未开始";
    } else if ([[NSDate date] timeIntervalSinceDate:endDate] > 0.0f) {
        return @"已结束";
    }
    
    return @"进行中";
}