XmlSerializer嵌套数组

Question

我需要获取XML的以下部分：

<TestInfo>
    //.....
    <Screenings>
       <UnitCodes>
          <UnitCode></UnitCode> <!-- Can be repeated -->
       </UnitCodes>
    </Screenings>
</TestInfo>

我有以下课程：

public class TestInfo
{
    //.... 
    [XmlArray("Screenings")]
    [XmlArrayItem("UnitCodes", typeof(Screening))]
    public List<Screening> Screenings { get; set; }
}

public class Screening
{
    [XmlArrayItem("UnitCode", typeof(string))]
    public List<string> UnitCodes { get; set; }
}

但它会生成：

<TestInfo>
    //.....
    <Screenings>
      <UnitCodes>
        <UnitCodes>
          <UnitCode>number</UnitCode>
        </UnitCodes>
      </UnitCodes>
    </Screenings>
</TestInfo>

如何删除不必要的（两次）UnitCodes节点？

谢谢！