Is it possible to modify the attribute of a property at runtime?

attributes, c#

Solution

It depends; from a reflection perspective: no. You can't. But if you are talking about attributes used by System.ComponentModel in things like data-binding, they you can use `TypeDescriptor.AddAttributes` to append extra attributes. Or other customer models involving custom descriptors. So it depends on the use-case.

In the case of xml serialization, it gets more interesting. Firstly, we can use fun object models:

using System;
using System.Xml.Serialization;
public class MyData
{
    [XmlAttribute]
    public int Id { get; set; }
    [XmlAttribute]
    public string Name { get; set; }
    [XmlIgnore]
    public bool NameSpecified { get; set; }

    static void Main()
    {
        var ser = new XmlSerializer(typeof(MyData));

        var obj1 = new MyData { Id = 1, Name = "Fred", NameSpecified = true };
        ser.Serialize(Console.Out, obj1);
        Console.WriteLine();
        Console.WriteLine();
        var obj2 = new MyData { Id = 2, Name = "Fred", NameSpecified = false };
        ser.Serialize(Console.Out, obj2);
    }
}

The `bool {name}Specified {get;set;}` pattern (along with `bool ShouldSerialize{name}()`) is recognised and used to control which elements to include.

Another alternative is to use the non-default ctor:

using System;
using System.Xml.Serialization;
public class MyData
{
    [XmlAttribute]
    public int Id { get; set; }
    public string Name { get; set; }

    static void Main()
    {
        var obj = new MyData { Id = 1, Name = "Fred" };

        XmlAttributeOverrides config1 = new XmlAttributeOverrides();
        config1.Add(typeof(MyData),"Name",
            new XmlAttributes { XmlIgnore = true});
        var ser1 = new XmlSerializer(typeof(MyData),config1); 
        ser1.Serialize(Console.Out, obj);
        Console.WriteLine();
        Console.WriteLine();
        XmlAttributeOverrides config2 = new XmlAttributeOverrides();
        config2.Add(typeof(MyData), "Name",
            new XmlAttributes { XmlIgnore = false });
        var ser2 = new XmlSerializer(typeof(MyData), config2);
        ser2.Serialize(Console.Out, obj);
    }
}

Note though that if you use this second approach you need to cache the serializer instance, as it emits an assembly every time you do this. I find the first approach simpler...

Problem

Original source