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  1. using System;
  2. using System.Collections.Generic;
  3.  
  4. public class Test
  5. {
  6. 	public static void Main()
  7. 	{
  8. 		// your code goes here
  9. 		Messenger m = new Messenger();
  10.         var sum = 0;
  11.         Action<int> messenger = x => sum += x;
  12. 		m.Register<int>(messenger);
  13. 		m.Send(42);
  14. 		Console.WriteLine(sum);
  15. 		m.Unregister<int>(messenger);
  16. 		m.Send(23);
  17. 		Console.WriteLine(sum);
  18. 	}
  19. }
  20.  
  21. /// <summary>
  22. /// Strongly-typed messenger system.
  23. /// </summary>
  24. public class Messenger
  25. {
  26.     /// <summary>
  27.     /// The actions. These are called when a message is sent.
  28.     /// </summary>
  29.     private readonly IDictionary<Type, Delegate> actions = new Dictionary<Type, Delegate>();
  30.  
  31.     /// <summary>
  32.     /// Register an action for a message.
  33.     /// </summary>
  34.     /// <typeparam name="T"> Type of message to receive. </typeparam>
  35.     /// <param name="action"> The action that is executed when the message is received. </param>
  36.     public void Register<T>(Action<T> action)
  37.     {
  38.         if (action == null)
  39.         {
  40.             throw new ArgumentNullException("action");
  41.         }
  42.  
  43.         var messageType = typeof(T);
  44.  
  45.         if (actions.ContainsKey(messageType))
  46.         {
  47.             actions[messageType] = Delegate.Combine(actions[messageType], action);
  48.         }
  49.         else
  50.         {
  51.             actions.Add(messageType, action);
  52.         }
  53.     }
  54.  
  55.     /// <summary>
  56.     /// Sends the specified message.
  57.     /// </summary>
  58.     /// <typeparam name="T"> The type of message. </typeparam>
  59.     /// <param name="message"> The message to send. </param>
  60.     public void Send<T>(T message)
  61.     {
  62.         var messageType = typeof(T);
  63.  
  64.         if (actions.ContainsKey(messageType))
  65.         {
  66.             ((Action<T>)actions[messageType])(message);
  67.         }
  68.     }
  69.  
  70.     /// <summary>
  71.     /// Unregister an action.
  72.     /// </summary>
  73.     /// <typeparam name="T"> The type of message. </typeparam>
  74.     /// <param name="action"> The action to unregister. </param>
  75.     public void Unregister<T>(Action<T> action)
  76.     {
  77.         var messageType = typeof(T);
  78.  
  79.         if (actions.ContainsKey(messageType))
  80.         {
  81.             actions[messageType] = (Action<T>)Delegate.Remove(actions[messageType], action);
  82.         }
  83.     }
  84. }
Runtime error #stdin #stdout #stderr 0.05s 27256KB
comments (?)
stdin
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Standard input is empty
stdout
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42
stderr
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Unhandled Exception:
System.NullReferenceException: Object reference not set to an instance of an object
  at Messenger.Send[Int32] (Int32 message) [0x00000] in <filename unknown>:0 
  at Test.Main () [0x00000] in <filename unknown>:0 
[ERROR] FATAL UNHANDLED EXCEPTION: System.NullReferenceException: Object reference not set to an instance of an object
  at Messenger.Send[Int32] (Int32 message) [0x00000] in <filename unknown>:0 
  at Test.Main () [0x00000] in <filename unknown>:0
https://ideone.com/85kzXX
language:
C# (gmcs 5.20.1)
created:
10 years ago
visibility:
public

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