Compiles into a library defining the RamdomSupplier attribute and the RandomMethod attribute

   

/*
Mastering Visual C# .NET
by Jason Price, Mike Gunderloy

Publisher: Sybex;
ISBN: 0782129110
*/

/*
  Example17_5a compiles into a library defining the RamdomSupplier attribute
  and the RandomMethod attribute
*/

using System;

// declare an attribute named RandomSupplier
[AttributeUsage(AttributeTargets.Class)]
public class RandomSupplier : Attribute
{
  public RandomSupplier()
  {
    // doesn't have to do anything
    // we just use this attribute to mark selected classes
  }
}

// declare an attribute named RandomMethod
[AttributeUsage(AttributeTargets.Method )]
public class RandomMethod : Attribute
{
  public RandomMethod()
  {
    // doesn't have to do anything
    // we just use this attribute to mark selected methods
  }
}
//===================================================
/*
  Example17_5b implements one class to supply random numbers
*/

// flag the class as a random supplier
[RandomSupplier]
public class OriginalRandom
{
  [RandomMethod]
  public int GetRandom()
  {
    return 5;
  }
}

//===================================================
/*
  Example17_5c implements one class to supply random numbers
*/

using System;

// flag the class as a random supplier
[RandomSupplier]
public class NewRandom
{
  [RandomMethod]
  public int ImprovedRandom()
  {
    Random r = new Random();
    return r.Next(1, 100);
  }
}

// this class has nothing to do with random numbers
public class AnotherClass
{
  public int NotRandom()
  {
    return 1;
  }
}
//===================================================
/*
  Example17_5d illustrates runtime type discovery
*/

using System;
using System.Reflection;

class Example17_5d 
{

  public static void Main(string[] args) 
  {

    RandomSupplier rs;
    RandomMethod rm;

    // iterate over all command-line arguments
    foreach(string s in args)
    {
      Assembly a = Assembly.LoadFrom(s);

      // Look through all the types in the assembly
      foreach(Type t in a.GetTypes())
      {
        rs = (RandomSupplier) Attribute.GetCustomAttribute(
         t, typeof(RandomSupplier));
        if(rs != null)
        {
          Console.WriteLine("Found RandomSupplier class {0} in {1}",
           t, s);
          foreach(MethodInfo m in t.GetMethods())
          {
            rm = (RandomMethod) Attribute.GetCustomAttribute(
             m, typeof(RandomMethod));
            if(rm != null)
            {
              Console.WriteLine("Found RandomMethod method {0}"
               , m.Name );
            }
          }        
        }
      }
    }

  }

}