用列表反序列化对象 <byte> XML的成员

Question

Have come across XML deserialization issue of class instances with List<byte> public properties when that properties have default definition in class constrictor

Say we have class:

public class TestClass
{
    public List<byte> ByteList;
    public TestClass()
    {
        this.ByteList = new List<byte>() { 0x01, 0x02 };
    }
}

then we have following code to test serialization/deserialization

TestClass testClass = new TestClass();
Console.WriteLine("testClass.ByteList.Count: {0}", testClass.ByteList.Count);

System.Xml.Serialization.XmlSerializer xmlSerializer = new System.Xml.Serialization.XmlSerializer(typeof(TestClass));
using (System.IO.FileStream fs = new System.IO.FileStream(@".\testClass.xml", System.IO.FileMode.OpenOrCreate))
{
    xmlSerializer.Serialize(fs, testClass);
}
Console.WriteLine("testClass.ByteList.Count: {0}", testClass.ByteList.Count);

TestClass deserializedTestClass = null;
using (System.IO.FileStream sr = new System.IO.FileStream(@".\testClass.xml", System.IO.FileMode.Open))
{
    deserializedTestClass = (TestClass)xmlSerializer.Deserialize(sr);
}
Console.WriteLine("deserializedTestClass.ByteList.Count: {0}", deserializedTestClass.ByteList.Count);

as a result we see on console following output:

testClass.ByteList.Count: 2

testClass.ByteList.Count: 2

deserializedTestClass.ByteList.Count: 4

serialization result xml is here:

<?xml version="1.0"?>
<TestClass xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <ByteList>
    <unsignedByte>1</unsignedByte>
    <unsignedByte>2</unsignedByte>
  </ByteList>
</TestClass>

Could somebody explain what is going on here and how to fix it?

Answer 1

The parameterless constructor for TestClass initializes ByteList to a non-empty list (ie with the values { 1, 2 }). Then the deserialization adds the two elements found in the XML to that non-empty list. So of course the list winds up with all 4 elements.