C# Language Reading an attribute from interface


There is no simple way to obtain attributes from an interface, since classes does not inherit attributes from an interface. Whenever implementing an interface or overriding members in a derived class, you need to re-declare the attributes. So in the example below output would be True in all three cases.

using System;
using System.Linq;
using System.Reflection;

namespace InterfaceAttributesDemo {
    [AttributeUsage(AttributeTargets.Interface, Inherited = true)]
    class MyCustomAttribute : Attribute {
        public string Text { get; set; }
    [MyCustomAttribute(Text = "Hello from interface attribute")]
    interface IMyClass {
        void MyMethod();
    class MyClass : IMyClass {
        public void MyMethod() { }
    public class Program {
        public static void Main(string[] args) {
        private static void GetInterfaceAttributeDemo() {
            var attribute1 = (MyCustomAttribute) typeof(MyClass).GetCustomAttribute(typeof(MyCustomAttribute), true);
            Console.WriteLine(attribute1 == null); // True
            var attribute2 = typeof(MyClass).GetCustomAttributes(true).OfType<MyCustomAttribute>().SingleOrDefault();
            Console.WriteLine(attribute2 == null); // True
            var attribute3 = typeof(MyClass).GetCustomAttribute<MyCustomAttribute>(true);
            Console.WriteLine(attribute3 == null); // True

One way to retrieve interface attributes is to search for them through all the interfaces implemented by a class.

var attribute = typeof(MyClass).GetInterfaces().SelectMany(x => x.GetCustomAttributes().OfType<MyCustomAttribute>()).SingleOrDefault();
Console.WriteLine(attribute == null); // False
Console.WriteLine(attribute.Text); // Hello from interface attribute