datePicker的简单使用方法：（注意连线）
- (IBAction)buttonpressed:(id)sender {
NSDate *selected = [datePicker date];
NSTimeZone *timeZone3 = [NSTimeZone timeZoneForSecondsFromGMT:3600*8];
NSDateFormatter *formatter3 = [[NSDateFormatter alloc] init];
[formatter3 setTimeZone:timeZone3];
[formatter3 setDateFormat:@"G YYYY-MM-dd EEEE aa HH:mm:ss Z"];
NSString *dateString = [formatter3 stringFromDate:selected];
NSString *message = [[NSString alloc]initWithFormat:@"The date and time you selected is : %@",dateString];
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Date and Time Selected" message:message delegate:nil cancelButtonTitle:@"Yes,I did" otherButtonTitles: nil];
[alert show];
[alert release];
[message release];
}