如何将多个IXmlSerializable序列化为一个XML文件？

Question

I have created a few specialized data structures that implements IXmlSerializable. At runtime, I want to serialize these instances into a single XML document (and deserialize).

Serializing to different files, XML result is correct. But when I tried to call XmlSerializer.Serialize consecutive times on a single StreamWriter for different data structures, the result is that it adds the XML declaration on each call, resulting in invalid XML.

What is the proper way to do this?

Do I need a wrapper parent class? If I use another parent class to wrap these data structures, and then serialize the parent class, how should I write implement IXmlSerialize at the parent?

Answer 1

Do I need a wrapper parent class?

Yes. The XmlSerializer isn't that smart. It outputs an XML file. It doesn't take into account that it might have some content already. You just get two XML files in one.

If fact, you don't need to implement IXmlSerializable at all if your data structure is simple. You can just serialize any class. This structure will suffice:

public class ParentClass
{
    public Class1 FirstClass {get;set;}
    public Class2 SecondClass {get;set;}
}

Just stuff it with your instances and you can XML serialize them.

---

In my case, I have an extension method to do all the serialization for me. This is it:

public static string ToXml<T>(this T value)
{
    StringWriter stringWriter = new StringWriter();

    string xml;

    XmlSerializer xmlserializer = new XmlSerializer(typeof(T));

    using (XmlWriter writer = XmlWriter.Create(stringWriter, new XmlWriterSettings { Indent = true }))
    {
        writer.WriteStartDocument();

        xmlserializer.Serialize(writer, value);
        writer.WriteEndDocument();

        xml = stringWriter.ToString();
    }

    return xml;
}

Then you can just call:

string xml = someInstanceOfParent.ToXml();

Save that as you like.

Answer 2

We can use the following approach: while serializing we write root node manually, then while deserializing skip this node manually.

public class One
{
    public string Foo { get; set; }
}

public class Two
{
    public string Bar { get; set; }
}


var one = new One { Foo = "foo" };
var two = new Two { Bar = "bar" };

// Serialization two different class in one file
var settings = new XmlWriterSettings { Indent = true };
using (var writer = XmlWriter.Create("test.txt", settings))
{
    // Create root node
    writer.WriteStartElement("root");

    var xs = new XmlSerializer(typeof(One));
    xs.Serialize(writer, one);

    xs = new XmlSerializer(typeof(Two));
    xs.Serialize(writer, two);
}

// Deserialization two different class from one file
using (var reader = XmlReader.Create("test.txt"))
{
    // Skip root node
    reader.ReadToFollowing("One"); // Name of first class

    var xs = new XmlSerializer(typeof(One));
    One first = (One)xs.Deserialize(reader);

    xs = new XmlSerializer(typeof(Two));
    Two second = (Two)xs.Deserialize(reader);
}