系统默认的是内容居左显示的，有时会觉得不太好看，可以实现代理方法。
- (UIView *)pickerView:(UIPickerView *)pickerView viewForRow:(NSInteger)row forComponent:(NSInteger)component reusingView:(UIView *)view
{
UILabel *label = [[[UILabel alloc] initWithFrame:CGRectMake(12.0f, 0.0f, [pickerView rowSizeForComponent:component].width-12, [pickerView rowSizeForComponent:component].height)] autorelease];
[label setText:[pickerData objectAtIndex:row]];
label.backgroundColor = [UIColor clearColor];
[label setTextAlignment:UITextAlignmentCenter];
return label;
}
设置初始默认值
[pickerView selectRow:3 inComponent:0 animated:NO];
转自：http://blog.csdn.net/xiaoxiangzhu660810/article/details/9271239