iOS中怎樣修改uipickerView的高度

UIDatePicker *datePicker = [[UIDatePicker alloc] init];

datePicker.frame = CGRectMake(0, 0, 320, 180);

[self addSubview:datePicker];

UIDatePicker *datePicker = [[UIDatePicker alloc] initWithFrame:CGRectMake(0, 0, 320, 180)];

[self addSubview:datePicker];