将日期转成具体的几分钟前，几小时前，昨天。。。

+ (NSString *)formatShowDateTime:(NSDate *)needDate
{
    if (needDate == nil) {
        
        return @"";
    }
    
    @try {
        //实例化一个NSDateFormatter对象
        
        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        
        NSDate * nowDate = [NSDate date];
        
        /////  将需要转换的时间转换成 NSDate 对象
        /////  取当前时间和转换时间两个日期对象的时间间隔
        /////  这里的NSTimeInterval 并不是对象，是基本型，其实是double类型，是由c定义的:  typedef double NSTimeInterval;
        NSTimeInterval time = [nowDate timeIntervalSinceDate:needDate];
        
        //// 再然后，把间隔的秒数折算成天数和小时数：
        
        NSString *dateStr = @"";
        
        if (time<=60) {  //// 1分钟以内的
            dateStr = @"1分钟前";
        }else if(time<=60*60){  ////  一个小时以内的
            
            int mins = time/60;
            dateStr = [NSString stringWithFormat:@"%d分钟前",mins];
            
        }else if(time<=60*60*24*2){   //// 在两天内的
            
            [dateFormatter setDateFormat:@"YYYY/MM/dd"];
            NSString * need_yMd = [dateFormatter stringFromDate:needDate];
            NSString *now_yMd = [dateFormatter stringFromDate:nowDate];
            
            [dateFormatter setDateFormat:@"HH:mm"];
            if ([need_yMd isEqualToString:now_yMd]) {
                //// 在同一天
                //                dateStr = [NSString stringWithFormat:@"今天 %@",[dateFormatter stringFromDate:needDate]];
                dateStr = [NSString stringWithFormat:@"%@",[dateFormatter stringFromDate:needDate]];
            }else{
                ////  昨天
                //                dateStr = [NSString stringWithFormat:@"昨天 %@",[dateFormatter stringFromDate:needDate]];
                [dateFormatter setDateFormat:@"dd"];
                NSString *beforeYesDay = [dateFormatter stringFromDate:needDate];
                NSString *yesDay = [dateFormatter stringFromDate:nowDate];
                NSInteger num = [yesDay integerValue] - [beforeYesDay integerValue];
                if (num == 1) {
                    dateStr = @"昨天";
                }else{
                    [dateFormatter setDateFormat:@"MM月dd日"];
                    dateStr = [dateFormatter stringFromDate:needDate];
                }
            }
        }else {
            
            [dateFormatter setDateFormat:@"yyyy"];
            NSString * yearStr = [dateFormatter stringFromDate:needDate];
            NSString *nowYear = [dateFormatter stringFromDate:nowDate];
            
            if ([yearStr isEqualToString:nowYear]) {
                ////  在同一年
                [dateFormatter setDateFormat:@"MM月dd日"];
                dateStr = [dateFormatter stringFromDate:needDate];
            }else{
                [dateFormatter setDateFormat:@"yyyy年MM月dd日"];
                dateStr = [dateFormatter stringFromDate:needDate];
            }
        }
        
        return dateStr;
    }
    @catch (NSException *exception) {
        return @"";
    }
}