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Attributes in C#

Attributes gives us the ability to associating metadata, or declarative information, with code (assemblies, types, methods, properties etc.). This is in C# done using [* and *], if you would like to add an attribute to a property:

[Description("This is a description of my property")]
public string MyProperty { get; set;}

Using reflection is it possible to retrieve the attributes. We are especially going to use this when working with Object-relational mapping (ORM) later in the course.

Example of reading an attribute using reflection:

using System;
using System.Reflection;
using System.ComponentModel;
public class Program{
    static void Main()
    {
        var propertyInfo = typeof(Test).GetProperty("MyProperty");
        var testDescriptionAttribute = (DescriptionAttribute)propertyInfo.GetCustomAttribute(typeof(DescriptionAttribute));
        Console.WriteLine(testDescriptionAttribute.Description);
    }
}
public class Test
{
    [Description("This is a description of my property")]
    public string MyProperty { get; set;}
}

.NET comes with a range of build in attributes, among these are:

Custom attributes

It's possible to define your own attributes. This done by creating a class which inherits from Attribute,

using System;
using System.Reflection;
using System.ComponentModel;
using System.Collections.Generic;
class Program{
    static void Main()
    {
        ShowTaxonomyAttribute(typeof(Wolf));
        ShowTaxonomyAttribute(typeof(Human));
    }
    static void ShowTaxonomyAttribute(Type type)
    {
        System.Attribute[] attrs = System.Attribute.GetCustomAttributes(type);
        foreach (System.Attribute attr in attrs)
        {
            if (attr is Taxonomy)
            {
                Taxonomy t = (Taxonomy)attr;
                System.Console.WriteLine(t);
            }
            else
            {
                Console.WriteLine($"Non-taxonomy attribute: {attr.TypeId}");
            }
        }
    }
}
[Taxonomy("Eukarya", Kingdom = "Animala", Specie = "Vulpes vulpes")]
public class Wolf
{
    public void MakeASound()
    {
        Console.WriteLine("Wooooooww!");
    }
}
[Description("This is a human")]
[Taxonomy("Eukarya", Kingdom = "Animala", Phylum = "Chordata", Class = "Mammalia", Order= "Primates", Genus ="Homo", Specie = "Homo sapiens", Family = "Hominidae")]
public class Human
{
    public void MakeASound()
    {
        Console.WriteLine("Hallo world");
    }
}
// Custom Taxonomy attribute
[System.AttributeUsage(System.AttributeTargets.Class)]

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6/7 Attributes

Attributes in C#

Custom attributes

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