NSDate和NSString

+(NSDate*) convertDateFromString:(NSString*)uiDate{    NSDateFormatter *formatter = [[NSDateFormatter alloc] init] ;    [formatter setDateFormat:@"yyyy年MM月dd日"];    NSDate *date=[formatter dateFromString:uiDate];    return date;} 输入的日期字符串形如：@"2012-07-30 13:08:08"- (NSDate *)dateFromString:(NSString *)dateString{NSDateFormatter *dateFormatter = [[NSDateFormatteralloc] init];[dateFormatter setDateFormat: @"yyyy-MM-dd HH:mm:ss"]; NSDate *destDate= [dateFormatter dateFromString:dateString];[dateFormatter release];return destDate;} - (NSString *)stringFromDate:(NSDate *)date{NSDateFormatter *dateFormatter = [[NSDateFormatteralloc] init]; //zzz表示时区，zzz可以删除，这样返回的日期字符将不包含时区信息。[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss zzz"];NSString *destDateString = [dateFormatter stringFromDate:date];[dateFormatter release];return destDateString;} //从起始日期经过一定天数后/前（day为负数）的日期- (NSString *)dateStringFromDate:(NSDate *)date afterDay:(int)day{    NSCalendar *calendar = [NSCalendar currentCalendar];    NSDateComponents *componentsToAdd = [[NSDateComponents alloc] init];    //这边填入需要增加的天数    [componentsToAdd setDay:day];    NSDateFormatter *dateFormatter=[[NSDateFormatter alloc] init];    [dateFormatter setDateFormat:@"yyyy-MM-dd"];    NSDate *fromDate=date;    NSDate *dateAfterDay = [calendar dateByAddingComponents:componentsToAdd toDate:fromDate options:0];    [componentsToAdd release];    NSString *dateStr = [dateFormatter stringFromDate:dateAfterDay];    [dateFormatter release];        return dateStr;}