Custom Attribute on property in C#

Question

I have a class Person with two properties

public sealed class Person
{
[Description("This is the first name")]
public string FirstName { get; set; }
[Description("This is the last name")]
public string LastName { get; set; }
}

In my console application code I'd like to get for each property of each instance the value of the Description Attribute.....

something similar to

Person myPerson = new Person();
myPerson.LastName.GetDescription() // method to retrieve the value of the attribute

Is it possible to do this task? Can someone suggest me a way? Best regards Fab

http://stackoverflow.com/questions/6637679/reflection-get-attribute-name-and-value-on-property — Nathan Cooper, Feb 10 '16 at 12:23
With that syntax no, it isn't possible. With other syntaxes it is possible (as shown for example in the linked question) — xanatos, Feb 10 '16 at 12:25

score 3 · Answer 1 · answered Feb 10 '16 at 12:27

The .LastName returns a string, so you can't do much from there. Ultimately, you need the PropertyInfo for this. There are two ways of getting that:

via an Expression (perhaps SomeMethod<Person>(p => p.LastName))
from a string (perhaps via nameof)

For example, you could do something like:

var desc = Helper.GetDescription<Person>(nameof(Person.LastName));

or

var desc = Helper.GetDescription(typeof(Person), nameof(Person.LastName));

with something like:

var attrib = (DescriptionAttribute)Attribute.GetCustomAttribute(
    type.GetProperty(propertyName), typeof(DescriptionAttribute));
return attrib?.Description;

Well, taking into account that nameof is available since C# 6.0 only. — Alexey Khoroshikh, Feb 10 '16 at 12:45

xanatos · Accepted Answer · 2016-02-10T12:33:27.483

With exactly that syntax it isn't possible. It is possible by using Expression Trees... For example:

public static class DescripionExtractor 
{
    public static string GetDescription<TValue>(Expression<Func<TValue>> exp) 
    {
        var body = exp.Body as MemberExpression;

        if (body == null) 
        {
            throw new ArgumentException("exp");
        }

        var attrs = (DescriptionAttribute[])body.Member.GetCustomAttributes(typeof(DescriptionAttribute), true);

        if (attrs.Length == 0) 
        {
            return null;
        }

        return attrs[0].Description;
    }
}

and then:

Person person = null;
string desc = DescripionExtractor.GetDescription(() => person.FirstName);

Note that the value of person is irrelevant. It can be null and everything will work correctly, because person isn't really accessed. Only its type is important.

Custom Attribute on property in C#

2 Answers2