nsdate 前一天 后一天

http://blog.sina.com.cn/s/blog_6568e7880100kfnh.html-(IBAction)prevDay:(id)sender{

    NSDateFormatter *format = [[NSDateFormatter alloc] init];
    [format setDateFormat:@"yyyy-MM-dd"];
    NSString * reportDate = [format stringFromDate:self.m_dataPicker.date];
    NSDate *date = [format dateFromString:reportDate];
    NSDate *newDate = [[NSDate alloc] initWithTimeIntervalSinceReferenceDate:([date timeIntervalSinceReferenceDate] - 24*3600)];
      reportDate = [format stringFromDate:newDate];
    [m_pickerButton setTitle:[[NSString alloc] initWithString:reportDate] forState:UIControlStateNormal];
    [m_dataPicker setDate:newDate animated:NO];
   
    [format release];
}

-(IBAction)nextDay:(id)sender{
    NSDateFormatter *format = [[NSDateFormatter alloc] init];
    [format setDateFormat:@"yyyy-MM-dd"];
    NSString *reportDate = [format stringFromDate:self.m_dataPicker.date];
    NSDate *date = [format dateFromString:reportDate];
    NSDate *newDate = [[NSDate alloc] initWithTimeIntervalSinceReferenceDate:([date timeIntervalSinceReferenceDate] + 24*3600)];
       reportDate = [format stringFromDate:newDate];
    
    [m_pickerButton setTitle:[[NSString alloc] initWithString:reportDate] forState:UIControlStateNormal];
    [m_dataPicker setDate:newDate animated:NO];
   
    
    [format release];
}