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C# Academy · Lesson

Light metaprogramming scenarios

Attribute driven helpers: display labels, required validation, mini constructor activator, and CSV like serialization with clear safety tips.

Plan & scope

Aim: Drive tiny behaviors with attributes.

  • Map labels
  • Validate required fields
  • Mini DI activator
  • Serialize to CSV like text

Attribute labels

Decorate properties with a DisplayName and reflect it to print friendly labels.

using System;
using System.Reflection;

[AttributeUsage(AttributeTargets.Property)]
public sealed class DisplayNameAttribute : Attribute
{
  public string Text { get; private set; }
  public DisplayNameAttribute(string text) { Text = text; }
}

public sealed class User
{
  [DisplayName("User Id")]
  public int Id { get; set; }

  [DisplayName("Full Name")]
  public string Name { get; set; }
}

public class Program
{
  static void PrintWithLabels(object o)
  {
    if (o == null) throw new ArgumentNullException("o");
    Type t = o.GetType();
    foreach (PropertyInfo p in t.GetProperties())
    {
      object[] at = p.GetCustomAttributes(typeof(DisplayNameAttribute), false);
      string label = at.Length > 0 ? ((DisplayNameAttribute)at[0]).Text : p.Name;
      object val = p.GetValue(o, null);
      Console.WriteLine(label + ": " + (val == null ? "null" : val.ToString()));
    }
  }

  public static void Main(string[] args)
  {
    User u = new User { Id = 1, Name = "Ada" };
    PrintWithLabels(u);
  }
}

All lessons in this course

  1. Type, MethodInfo, activation, custom attributes
  2. Source-level info (Caller attributes)
  3. Light metaprogramming scenarios
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