how to serialize some attribute in some condition

Question

When using XML serialization to serialize a class, how to make some attribute be outputted conditionally. i.e. In some case, it output this attribute, in other cases, it does not.

Answer 1

You can create an additional property which is called MyPropertySpecified, which returns a boolean.
When this property returns true, the MyProperty property will be serialized. When it returns false, it will not be serialized.

Also, you'd want to decorate that property with the XmlIgnoreAttribute, so that this specific property is not serialized.

Example:

public class Person
{
    public string Name
    {
        get;
        set;
    }

    [XmlIgnore]
    public bool NameSpecified
    {
        get  { return Name != "secret"; }
    }
}

Answer 2

While works and is a rather short solution, the propertyNameSpecified pattern has some drawbacks in my opinion (pollutes the interface of your class; relies on property names; introduces implicit behavior).

If you only need to implement a simple condition (e.g. don't serialize a default value), then the DefaultValue attribute is a better choice.

For example:

public class PurchaseOrder
{
    [DefaultValue("2002")]
    public string Year;
}

If Year has the value "2002", it will be omitted from the XML output.