How to create a custom attribute in C#?

Question

Amrith Chandran · Answer

In C#, you can create your own custom attributes, which are pieces of metadata associated with your code elements: classes, methods, properties, etc., that can later be read through reflection.
Let's see the step-by-step guide to create a custom attribute in C#.
and 
Create a Custom Attribute Class
A custom attribute is simply a class that derives from System.Attribute namespace.
and 
using System;
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method | AttributeTargets.Property, AllowMultiple = false)]
public class AuthorAttribute : Attribute
{
   public string UserName { get; }
   public string Version { get; set; }
   public AuthorAttribute(string name)
   {
       UserName = name;
       Version = "1.0";
   }
} 
and 
Note: AttributeTargets.Class is allowed to use this attribute with the classes,
AttributeTargets.Method is allowed to use with methods and and and AttributeTargets.Property allows to use of properties. You can also allow this attribute to be used only with the call by setting the
AttributeTargets.Class.
You can also allow multiple uses with AllowMultiple = true.
and 
Apply the Attribute
Now you can use this attribute to decorate your class, method, or property:
[Author("Manish Sharma", Version = "2.3")]
public class ClassName
{
   [Author("Pooja Verma")]
   public void MethodName()
   {
       Console.WriteLine("Hello C# developer");
   }
}
and 
Retrieve the Attribute via Reflection
You can read attribute data at runtime like given below:
using System;
using System.Reflection;
class Program
{
   static void Main()
   {
       Type type = typeof(ClassName);
       // Get class attribute
       var classAttr = (AuthorAttribute)Attribute.GetCustomAttribute(type, typeof(AuthorAttribute));
       Console.WriteLine($"Class Author: {classAttr.UserName}, Version: {classAttr.Version}");
       // Get method attribute
       MethodInfo method = type.GetMethod("MethodName");
       var methodAttr = (AuthorAttribute)Attribute.GetCustomAttribute(method, typeof(AuthorAttribute));
       Console.WriteLine($"Method Author: {methodAttr.UserName}, Version: {methodAttr.Version}");
   }
}
and 
Output
Class Author: Manish Sharma, Version: 2.3
Method Author: John Doe, Version: 1.0
and 
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How to create a custom attribute in C#?

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