Serialize only changed properties of the object

Question

In C# is it possible to serialize object with only the modified values?

For example: I have instance of the Button object bind into the PropertyGrid and I want to serialize that Button object with only the changed properties. In C# what was the best approach to archive this?

Answer 1

In your own types: yes, you can support this - via the ShouldSerialize* pattern, for example:

public string Name {get;set;}
public bool ShouldSerializeName() { return Name != null; }

However, on external types - it is entirely up to them whether they support this. Note that this will also tell the property-grid which to embolden.

In some cases, [DefaultValue({the default value})] will also work.

Answer 2

You can iterate object's properties through reflection, compare it's properties with 'fresh' instance, and write down the difference somehow. But you should address many problems if you choose that path, like null handling, serializing non-serializable types, serializing references, etc. Here's just a sketch:

    public static string ChangedPropertiesToXml<T>(T changedObj)
    {
        XmlDocument doc=new XmlDocument();
        XmlNode typeNode = doc.CreateNode(XmlNodeType.Element, typeof (T).Name, "");
        doc.AppendChild(typeNode);
        T templateObj = Activator.CreateInstance<T>();
        foreach (PropertyInfo info in
            typeof (T).GetProperties(BindingFlags.Instance | BindingFlags.Public))
        {
            if (info.CanRead && info.CanWrite)
            {
                object templateValue = info.GetValue(templateObj, null);
                object changedValue = info.GetValue(changedObj, null);
                if (templateValue != null && changedValue != null && !templateValue.Equals(changedValue))
                {
                    XmlElement elem =  doc.CreateElement(info.Name);
                    elem.InnerText = changedValue.ToString();
                    typeNode.AppendChild(elem);
                }
            }
        }
        StringWriter sw=new StringWriter();
        doc.WriteContentTo(new XmlTextWriter(sw));
        return sw.ToString();
    }

A call:

Button b = new Button();
b.Name = "ChangedName";
Console.WriteLine(SaveChangedProperties(b));

An output:

<Button>
   <Name>ChangedName</Name>
</Button>