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;
}