Question

I’m trying to serialize a class derived from List<> using DataContract. The problem is that properties of my class won’t get serialized.

My classes:

[CollectionDataContract] /*[Serializable]*/ /*[DataContract]*/
public class DownloadRuleCollection : List<DownloadRule> {

    [DataMember(EmitDefaultValue = false)]
    public string SomeProperty { get; set; }
    //this is, in fact, more complex, but this is enough for the example
}

[DataContract]
public class DownloadRule {
    [DataMember(EmitDefaultValue = false)]
    public string Name { get; set; }

    /*
     more properties
     ...
     */
}

Test:

static void Main(string[] args) {

    //fill test collection with some data...
    var col = new DownloadRuleCollection { SomeProperty = "someText" };

    var rule = new DownloadRule { Name = "test01" };
    col.Add(rule);

    rule = new DownloadRule { Name = "test02" };
    col.Add(rule);

    rule = new DownloadRule { Name = "test03" };
    col.Add(rule);

    //serialize
    Console.WriteLine("serializing");

    Serialize(col, "serializationTest.xml");

    Console.WriteLine("serialized");
    Console.ReadLine();
}

result:

<?xml version="1.0" encoding="utf-8"?>
<ArrayOfDownloadRule xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/ConsoleApplication1">
  <DownloadRule>
    <Name>test01</Name>
  </DownloadRule>
  <DownloadRule>
    <Name>test02</Name>
  </DownloadRule>
  <DownloadRule>
    <Name>test03</Name>
  </DownloadRule>
</ArrayOfDownloadRule>

As you can see, the List’s items are serialized (and deserialized) properly, but the List itself does not get serialized. I have tried to use different attributes:
[Serializable], no change;
[DataContract], throws exception during serialization (collections cant use this attribute)

btw I am serializing also private fields, so I cannot use XmlSerializer (or other classes that can’t serialize private fields).

Answer 1

Ok, so Climber104’s solution would work, but I would need to re-implement all of the List‘s methods, which makes me feel that I am reinventing the wheel.

JaredPar from Jarek Waliszko’s thread suggests to use a wrapper class.
The easiest is to use it just for the sake of serialization process, so I used an protected innner wrapper class. This allows me to achieve my goals with just a few lines of code needed.

public class DownloadRuleCollection : List<DownloadRule> {

    public string SomeProperty { get; set; }

    public void Serialize(string fileName) {
        Serializer.Serialize(
            new DownloadRuleCollection_SerializationWrapper {
                Collection = this,
                SomeProperty = SomeProperty
            }, fileName);
    }

    public static DownloadRuleCollection Deserialize(string fileName) {
        var wrapper = Serializer.Deserialize<DownloadRuleCollection_SerializationWrapper>(fileName);

        var result = wrapper.Collection;
        result.SomeProperty = wrapper.SomeProperty;

        return result;
    }

    [DataContract(Name = "DownloadRuleCollection")]
    private class DownloadRuleCollection_SerializationWrapper {

        [DataMember(EmitDefaultValue = false, Name = "SomeProperty", Order = 0)]
        public string SomeProperty { get; set; }

        [DataMember(EmitDefaultValue = false, Name = "DownloadRules", Order = 1)]
        public DownloadRuleCollection Collection;

    }
}

[DataContract]
public class DownloadRule {
    [DataMember(EmitDefaultValue = false)]
    public string Name { get; set; }
}

public static class Serializer {
    public static void Serialize<T>(T obj, string fileName) {
        using(XmlWriter writer = XmlWriter.Create(fileName, new XmlWriterSettings { Indent = true }))
            new DataContractSerializer(typeof(T)).WriteObject(writer, obj);
    }

    public static T Deserialize<T>(Stream stream) {
        return (T)new DataContractSerializer(typeof(T)).ReadObject(stream);
    }

    public static T Deserialize<T>(string fileName) {
        using(FileStream fs = File.OpenRead(fileName)) {
            return Deserialize<T>(fs);
        }
    }
}