Type, MethodInfo, activation, custom attributes

using System;

public class Sample { }

public class Program
{
  public static void Main(string[] args)
  {
    // 1) From a compile-time type
    Type t1 = typeof(Sample);

    // 2) From an instance
    Sample s = new Sample();
    Type t2 = s.GetType();

    // 3) From a full name (needs assembly-qualified name for external types)
    Type t3 = Type.GetType("System.String");

    Console.WriteLine(t1.Name + ", " + t2.FullName + ", " + (t3 == null ? "null" : t3.Name));
  }
}

using System;
using System.Reflection;

public class Greeter
{
  public string Hello(string name) { return "Hello, " + name; }
}

public class Program
{
  public static void Main(string[] args)
  {
    Greeter g = new Greeter();
    Type t = typeof(Greeter);

    MethodInfo mi = t.GetMethod("Hello"); // public instance method
    object result = mi.Invoke(g, new object[] { "Ada" }); // call dynamically

    Console.WriteLine(result); // Hello, Ada
  }
}

using System;

public class Person
{
  public string Name { get; set; }
  public Person() { Name = "Unknown"; } // parameterless ctor
}

public class Program
{
  public static void Main(string[] args)
  {
    Type tp = typeof(Person);
    object o = Activator.CreateInstance(tp); // uses public parameterless ctor
    Person p = (Person)o;
    p.Name = "Alan";
    Console.WriteLine("Created: " + p.Name);
  }
}

using System;
using System.Reflection;

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)]
public sealed class LabelAttribute : Attribute
{
  public string Text { get; private set; }
  public LabelAttribute(string text) { Text = text; }
}

[Label("Utility class")]
public class Utils
{
  [Label("Adds two ints")]
  public static int Add(int a, int b) { return a + b; }
}

public class Program
{
  public static void Main(string[] args)
  {
    Type t = typeof(Utils);

    // Read class attribute
    object[] classAttrs = t.GetCustomAttributes(typeof(LabelAttribute), false);
    if (classAttrs.Length > 0)
      Console.WriteLine("Class label: " + ((LabelAttribute)classAttrs[0]).Text);

    // Read method attribute
    MethodInfo mi = t.GetMethod("Add");
    object[] methodAttrs = mi.GetCustomAttributes(typeof(LabelAttribute), false);
    if (methodAttrs.Length > 0)
      Console.WriteLine("Method label: " + ((LabelAttribute)methodAttrs[0]).Text);
  }
}