NSDate和NSString之间的转换以及时区的问题

以下是具体的例子：

<span style="font-family:Microsoft YaHei;font-size:12px;"> NSDate *date1=[NSDate date];
NSLog(@"date1: %@",date1);

NSDateFormatter *format=[[NSDateFormatter alloc]init];
[format setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
NSString *str1=[format stringFromDate:date1];
NSLog(@"date1Srting:%@",str1);

NSDate *date2= [format dateFromString:str1];
NSLog(@"date2: %@",date2);

NSDate *date3=[NSDate date];
NSTimeZone *zone =[NSTimeZone systemTimeZone];
NSInteger interval = [zone secondsFromGMTForDate: date3];
NSDate *localDate =[date3 dateByAddingTimeInterval: interval];
NSLog(@"date3: %@",localDate);</span>
结果：
2015-02-11 17:04:31.784 OCStudy-block[6277:150502] date1: 2015-02-11 09:04:31 +0000
2015-02-11 17:04:31.784 OCStudy-block[6277:150502] date1Srting:2015-02-11 17:04:31
2015-02-11 17:04:31.784 OCStudy-block[6277:150502] date2: 2015-02-11 09:04:31 +0000
2015-02-11 17:04:31.784 OCStudy-block[6277:150502] date3: 2015-02-11 17:04:31 +0000


从上可以看出 ，系统获取到的时间比我们本地时间要慢8小时，date2经过NSDateFormatter转化之后比原理晚了8小时，跟我们测试的本地时间相同，而date3显示则是符合我们的要求，具体解析参见http://www.educity.cn/wenda/153791.html