将后台的时间数据转换为类似微信发动态几分钟前、几天前、几月前
NSString+Time.h

#import <Foundation/Foundation.h>

@interface NSString (Time)
+ (NSString *) compareCurrentTime:(NSString *)str;
@end

NSString+Time.m

#import "NSString+Time.h"

@implementation NSString (Time)
+ (NSString *) compareCurrentTime:(NSString *)str
{
    
    //把字符串转为NSdate
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss.SSS"];
    NSDate *timeDate = [dateFormatter dateFromString:str];
    
    //得到与当前时间差
    NSTimeInterval  timeInterval = [timeDate timeIntervalSinceNow];
    timeInterval = -timeInterval;
    //标准时间和北京时间差8个小时
//    timeInterval = timeInterval - 8*60*60;
    long temp = 0;
    NSString *result;
    if (timeInterval < 60) {
        result = [NSString stringWithFormat:@"刚刚"];
    }
    else if((temp = timeInterval/60) <60){
        result = [NSString stringWithFormat:@"%ld分钟前",temp];
    }
    
    else if((temp = temp/60) <24){
        result = [NSString stringWithFormat:@"%ld小时前",temp];
    }
    
    else if((temp = temp/24) <30){
        result = [NSString stringWithFormat:@"%ld天前",temp];
    }
    
    else if((temp = temp/30) <12){
        result = [NSString stringWithFormat:@"%ld月前",temp];
    }
    else{
        temp = temp/12;
        result = [NSString stringWithFormat:@"%ld年前",temp];
    }
    
    return  result;
}


@end