datePicker改变大小问题

_datePick = [[UIDatePicker alloc]init];
if (iPhone4 || iPhone5) {
_datePick.frame = CGRectMake(0, 15/568.0*SCREEN_H, SCREEN_W-60 , 185/568.0*SCREEN_H);
}else
{
_datePick.frame = CGRectMake(0, 15/568.0*SCREEN_H, SCREEN_W-60 , 200/568.0*SCREEN_H);
}
_datePick.datePickerMode = UIDatePickerModeDate;

_datePick.backgroundColor = [UIColor whiteColor];
[_DateView addSubview:_datePick];

//下面的是错误的
_datePick = [[UIDatePicker alloc]initWithFrame:CGRectMake(20, 100, 300, 150)];//创建的时候用这种方法是不会改变大小的。