Parametrize generic event system - c#

I'm not sure if this has been asked before, but I really didn't know how to look for it, as I am not exactly sure what this thing / what I'm trying to do is exactly called...
I have an delegate-based messaging generic system that I use in Unity3D - taken from here.
[UA Crosslink]
It is used like this:
// Writing an event listener
void OnSpeedChanged(float speed)
{
this.speed = speed;
}
// Registering an event listener
void OnEnable()
{
Messenger<float>.AddListener("speed changed", OnSpeedChanged);
}
// Unregistering an event listener
void OnDisable()
{
Messenger<float>.RemoveListener("speed changed", OnSpeedChanged);
}
The problem I'm having, is that the code is currently very un-DRY (there's a lot of copy paste), and I want to DRY it, by hopefully parametrizing it, making it more generic.
I will post the relevant code - Please note that you don't really have to understand the code in detail and what's its doing, in order to answer.
Here's a class that does stuff behind the scene:
static internal class MessengerInternal
{
static public Dictionary<string, Delegate> eventTable = new Dictionary<string, Delegate>();
static public readonly MessengerMode DEFAULT_MODE = MessengerMode.REQUIRE_LISTENER;
static public void OnListenerAdding(string eventType, Delegate listenerBeingAdded)
{
if (!eventTable.ContainsKey(eventType)) {
eventTable.Add(eventType, null);
}
Delegate d = eventTable[eventType];
if (d != null && d.GetType() != listenerBeingAdded.GetType()) {
throw new ListenerException(string.Format("Attempting to add listener with inconsistent signature for event type {0}. Current listeners have type {1} and listener being added has type {2}", eventType, d.GetType().Name, listenerBeingAdded.GetType().Name));
}
}
static public void OnListenerRemoving(string eventType, Delegate listenerBeingRemoved)
{
if (eventTable.ContainsKey(eventType)) {
Delegate d = eventTable[eventType];
if (d == null) {
throw new ListenerException(string.Format("Attempting to remove listener with for event type {0} but current listener is null.", eventType));
}
else if (d.GetType() != listenerBeingRemoved.GetType()) {
throw new ListenerException(string.Format("Attempting to remove listener with inconsistent signature for event type {0}. Current listeners have type {1} and listener being removed has type {2}", eventType, d.GetType().Name, listenerBeingRemoved.GetType().Name));
}
}
else {
throw new ListenerException(string.Format("Attempting to remove listener for type {0} but Messenger doesn't know about this event type.", eventType));
}
}
static public void OnListenerRemoved(string eventType)
{
if (eventTable[eventType] == null) {
eventTable.Remove(eventType);
}
}
static public void OnBroadcasting(string eventType, MessengerMode mode)
{
if (mode == MessengerMode.REQUIRE_LISTENER && !eventTable.ContainsKey(eventType)) {
throw new BroadcastException(string.Format("Broadcasting message {0} but no listener found.", eventType));
}
}
}
Now, I have generic messenger classes, that have either one, two, three or even no arguments - So the user could choose a suitable event handler to subscribe to an event.
Here's the version, that takes no generic arguments:
// No parameters
static public class Messenger {
private static Dictionary<string, Delegate> eventTable = MessengerInternal.eventTable;
static public void AddListener(string eventType, Callback handler) {
MessengerInternal.OnListenerAdding(eventType, handler);
eventTable[eventType] = (Callback)eventTable[eventType] + handler;
}
static public void RemoveListener(string eventType, Callback handler) {
MessengerInternal.OnListenerRemoving(eventType, handler);
eventTable[eventType] = (Callback)eventTable[eventType] - handler;
MessengerInternal.OnListenerRemoved(eventType);
}
static public void Broadcast(string eventType) {
Broadcast(eventType, MessengerInternal.DEFAULT_MODE);
}
static public void Broadcast(string eventType, MessengerMode mode) {
MessengerInternal.OnBroadcasting(eventType, mode);
Delegate d;
if (eventTable.TryGetValue(eventType, out d)) {
Callback callback = d as Callback;
if (callback != null) {
callback();
} else {
throw MessengerInternal.CreateBroadcastSignatureException(eventType);
}
}
}
}
Here's the version that takes one arg, (I just copy paste and add a T):
// One parameter
static public class Messenger<T> {
private static Dictionary<string, Delegate> eventTable = MessengerInternal.eventTable;
static public void AddListener(string eventType, Callback<T> handler) {
MessengerInternal.OnListenerAdding(eventType, handler);
eventTable[eventType] = (Callback<T>)eventTable[eventType] + handler;
}
static public void RemoveListener(string eventType, Callback<T> handler) {
MessengerInternal.OnListenerRemoving(eventType, handler);
eventTable[eventType] = (Callback<T>)eventTable[eventType] - handler;
MessengerInternal.OnListenerRemoved(eventType);
}
static public void Broadcast(string eventType, T arg1) {
Broadcast(eventType, arg1, MessengerInternal.DEFAULT_MODE);
}
static public void Broadcast(string eventType, T arg1, MessengerMode mode) {
MessengerInternal.OnBroadcasting(eventType, mode);
Delegate d;
if (eventTable.TryGetValue(eventType, out d)) {
Callback<T> callback = d as Callback<T>;
if (callback != null) {
callback(arg1);
} else {
throw MessengerInternal.CreateBroadcastSignatureException(eventType);
}
}
}
}
As you might have already guessed, the one that takes two args, I just copy paste again, and add another generic type, like <T, U> etc.
This is the part that I'm trying to eliminate - But yet I have no idea how.
More accurately, what I'm looking for is: Only one Messenger class, but yet I am able to do:
Messenger<float>.Subscribe("player dead", OnDead);
Messenger<int, bool>.Subscribe("on something", OnSomething);
Messenger<bool, float, MyType>.Subscribe( stuff );
Or, (doesn't really matter which)
Messenger.Subscribe<float> ("player dead", OnDead);
You got the idea...
How can I do that, how can I write a generic messenger, that when I want to add yet another generic arg, I don't have to copy-paste and write a whole other version, just cause I needed an extra arg?
Thanks a lot!

You have a messenger but you don't seem to be sending any messages! You are trying to send the contents without a proper envelope. Wrap the values you want to send out in a class that represents your actual message and you can then subscribe to the type of the message which will contain all the values you were trying to send.
public class PlayerSpeedChangedMessage {
public Guid PlayerId { get; set; }
public int OldSpeed { get; set; }
public int NewSpeed { get; set; }
}
public class MyMessageHandler {
public MyMessageHandler() {
Messenger<PlayerSpeedChangedMessage>.Subscribe(OnDead);
}
HandleSpeedChange(PlayerSpeedChangedMessage message) {
// Do stuff with the message
}
}

I think for C# developers that Message class on the wiki is a little out-moded. C# and even Unity itself has a fairly nice messaging system already in place (As long as your needs aren't too complex). Check out SendMessage and BroadcastMessage.

Related

How to use params of object in Action

While creating a UI system, I am trying to create a UI event handler that takes a variable length parameter and performs an action.
Here is my code
class UIEventTriggerManager : MonoBehaviour
{
public static UIEventTriggerManager Instance;
private void Awake()
{
Instance = this;
}
public void Publish(string key, params object[] args)
{
m_eventHandler[key]?.Invoke(args);
}
public void Subscribe(string eventName, Action<object[]> action)
{
if (m_eventHandler.ContainsKey(eventName) == false)
{
m_eventHandler.Add(eventName, action);
}
else
{
m_eventHandler[eventName] += action;
}
}
}
class CharacterUI
{
public void FirstOpen()
{
UIEventTriggerManager.Instance.Subscribe("ChagedCharacter", ChagedCharacter); // ChagedCharacter error
UIEventTriggerManager.Instance.Subscribe("ChagedCharacter2", ChagedCharacter2); // error
UIEventTriggerManager.Instance.Subscribe("ChagedCharacter3", ChagedCharacter3); // error
}
public void ChagedCharacter()
{
//....
}
public void ChagedCharacter2(int a)
{
//....
}
public void ChagedCharacter3(int a, string b, float c)
{
//....
}
}
How to use Subscribe 'ChangedCharacter' Method??
Do I have to add 'params object[] args' to the method argument??
I know syntax error but I need an event handler to manage multiple parameters.
I'm trying to implement it this way, please give me some advice.
The params does only exist in the signature of
Publish(string key, params object[] args)
meaning you can call this method with additional parameters - or not. Inside this method it is simply an object[] of variable length. If no args was passed in at all it will simply be an empty array.
Also yourself already seem to know that Action<object[]> simply takes an object[] - no params here.
Action<object[]> basically is nothing else than a shorthand for
public delegate void SomeName(object[] args);
Therefore also the listener method is simply
// Should it be "Changed" btw?
public void ChagedCharacter(object[] args)
and it is the responsibility of this (and any listener) to correctly handle the array.
The error should actually tell you exactly which signature ChagedCharacter was expected to have.
You could then e.g. do
private void ChagedCharacter(object[] args)
{
switch(args.Length)
{
case 0:
ChagedCharacter ();
break;
case 1 when args[0] is int intValue :
ChagedCharacter (intValue);
break;
case 3 when args[0] is int intValue && args[1] is string stringValue && args[2] is float floatValue:
ChagedCharacter (intValue, stringValue, floatValue);
break;
default:
break;
}
}
But honestly before you do that you rather overthink your design ...
Maybe this solution is enough for you. and this solution also have boxing unboxing , So maybe can use <T> to replace object[] to avoid.
public enum EventType
{
ChagedCharacter,
ChagedCharacter2
}
public class UIEventTriggerManager : MonoBehaviour
{
public static UIEventTriggerManager Instance;
private void Awake()
{
Instance = this;
}
static Dictionary<EventType, List<IReciveEvent>> recives = new Dictionary<EventType, List<IReciveEvent>>();
public void Publish(EventType key, params object[] args)
{
if (recives.ContainsKey(key))
{
foreach(IReciveEvent ir in recives[key])
{
ir.GetEvent(key,args);
}
}
}
public void Subscribe(EventType type , IReciveEvent ui)
{
if(!recives.ContainsKey(type))
{
recives[type] = new List<IReciveEvent>();
}
if(!recives[type].Contains(ui))
{
recives[type].Add(ui);
}
}
}
public interface IReciveEvent
{
void GetEvent(EventType type, object[] objs);
}
public class CharUI : MonoBehaviour, IReciveEvent
{
private void Awake()
{
UIEventTriggerManager.Instance.Subscribe(EventType.ChagedCharacter, this);
UIEventTriggerManager.Instance.Subscribe(EventType.ChagedCharacter2, this);
}
public void GetEvent(EventType type, object[] objs)
{
if(type == EventType.ChagedCharacter)
{
//todo
}
else if ( type == EventType.ChagedCharacter2)
{
int a = (int)objs[0];
//todo
}
//....
}
}

Adapting C# event containing ref parameter

I'm in a situation where I have to use 3rd party library that contains a lot of events and is imho not very well written. It fires up events that I have to handle in my code, but I'm trying to abstract it away (to be able to unit test rest of my code dependent on that library) so I need an adapter. The problem is that some of the events are of delegate type that take ref parameters. Here's an example of how the 3rd party library looks like:
delegate void AdapteeEventHandler1(SpecificAdaptee sender, int a, int b);
delegate void AdapteeEventHandler2(SpecificAdaptee sender, ref int a); // problematic delegate
class SpecificAdaptee
{
public event AdapteeEventHandler1 Event1;
public event AdapteeEventHandler2 Event2; // problematic event
/// <summary>Exercise Event1</summary>
public void FireEvent1()
{
Event1?.Invoke(this, 1, 2);
}
/// <summary>Exercise Event2</summary>
public void FireEvent2()
{
int a = 42;
Event2?.Invoke(this, ref a);
}
}
To show how I am abstracting regular event taking list of parameters, it contains Event1 of type AdapteeEventHandler1. The problematic type is AdapteeEventHandler2, but let me show first how I am going about adapting the whole thing:
#region AdaptedEventArgs
class AdaptedEventArgs1 : EventArgs
{
public int A { get; set; }
public int B { get; set; }
}
class AdaptedEventArgs2 : EventArgs
{
public int A { get; set; }
}
#endregion
/// <summary>These represent an abstraction layer between SpecificAdaptee and our own code</summary>
class Adaptor
{
private readonly SpecificAdaptee _specificAdaptee;
/// <summary>Maintains relationship between the event triggered by SpecificAdaptee and the adapted event.</summary>
private readonly IAdaptedEventHandlerManager _adaptedEventHandlerManager;
public Adaptor(SpecificAdaptee specificAdaptee, IAdaptedEventHandlerManager adaptedEventHandlerManager)
{
_specificAdaptee = specificAdaptee;
_adaptedEventHandlerManager = adaptedEventHandlerManager;
}
#region Events
/// <summary>Adapts SpecificAdaptee.Event1</summary>
public event EventHandler<AdaptedEventArgs1> AdaptedEvent1
{
add
{
_specificAdaptee.Event1 += _adaptedEventHandlerManager.RegisterEventHandler<AdapteeEventHandler1>(value,
(sender, a, b) => value.Invoke(this, new AdaptedEventArgs1 { A = a, B = b }));
}
remove
{
_specificAdaptee.Event1 -= _adaptedEventHandlerManager.UnregisterEventHandler<AdapteeEventHandler1>(value);
}
}
/// <summary>Adapts SpecificAdaptee.Event2</summary>
public event EventHandler<AdaptedEventArgs2> AdaptedEvent2
{
add
{
/* !!! ERROR HERE !!! */
_specificAdaptee.Event2 += _adaptedEventHandlerManager.RegisterEventHandler<AdapteeEventHandler2>(value,
(sender, a) => value.Invoke(this, new AdaptedEventArgs2 { A = a }));
}
remove
{
_specificAdaptee.Event2 -= _adaptedEventHandlerManager.UnregisterEventHandler<AdapteeEventHandler2>(value);
}
}
#endregion
}
So what is happening here is that when I register an event handler to Adaptor.AdaptedEvent1 I am wrapping EventHandler<AdaptedEventArgs1> in AdapteeEventHandler1 and register it to SpecificAdaptee.Event1, also converting the AdaptedEventArgs1 to list of parameters required by AdapteeEventHandler1. This way user can register to events of Adaptor that will be fired when SpecificAdaptee fires its own events. Next I will post a program that exercises this but note that the problem is in AdaptedEvent2, where I would like to do things in an analogous manner, but I don't know how to deal with the ref parameter (there is a syntax error in add accessor of AdaptedEvent2.
Here is a console application exercising the project:
class Program
{
public static void Main(string[] args)
{
var specific = new SpecificAdaptee();
var adapter = new Adaptor(specific, new AdaptedEventHandlerManager());
adapter.AdaptedEvent1 += OnAdaptedEvent1;
adapter.AdaptedEvent2 += OnAdaptedEvent2;
specific.FireEvent1();
specific.FireEvent2();
Console.ReadLine();
}
private static void OnAdaptedEvent1(object sender, AdaptedEventArgs1 args)
{
Console.WriteLine($"{nameof(OnAdaptedEvent1)}({sender}, {args.A}, {args.B})");
}
private static void OnAdaptedEvent2(object sender, AdaptedEventArgs2 args)
{
Console.WriteLine($"{nameof(OnAdaptedEvent2)}({sender}, {args.A})");
}
}
So that's how it's supposed to work. I register to events of my Adaptor that I have in my code, and events get fired when the 3rd party library (SpecificAdaptee) fires its own events (here in this example, triggered by calling specific.FireEvent1() and 2).
For completeness, so you can try it yourself I include code for AdaptedEventHandlerManager that maps adapted event handlers to SpecificAdaptee's handlers, so I can register and unregister multiple event handlers like I normally would do:
interface IAdaptedEventHandlerManager
{
TSpecificEventHandler RegisterEventHandler<TSpecificEventHandler>(object adaptedEventHandler,
TSpecificEventHandler specificEventHandler);
TSpecificEventHandler UnregisterEventHandler<TSpecificEventHandler>(object adaptedEventHandler)
where TSpecificEventHandler : class;
}
class AdaptedEventHandlerManager : IAdaptedEventHandlerManager
{
/// <summary>
/// Remembers relation between the specific handler and general handler. Important when unsubscribing from
/// events. Key is the general event handler we are registering to events of this class. Value are specific
/// event handlers.
/// </summary>
private readonly Dictionary<object, List<object>> _eventHandlers =
new Dictionary<object, List<object>>();
public TSpecificEventHandler RegisterEventHandler<TSpecificEventHandler>(object adaptedEventHandler,
TSpecificEventHandler specificEventHandler)
{
List<object> eventHandlerList;
if (!_eventHandlers.TryGetValue(adaptedEventHandler, out eventHandlerList))
{
eventHandlerList = new List<object> { specificEventHandler };
_eventHandlers.Add(adaptedEventHandler, eventHandlerList);
}
else
{
eventHandlerList.Add(specificEventHandler);
}
return specificEventHandler;
}
public TSpecificEventHandler UnregisterEventHandler<TSpecificEventHandler>(object adaptedEventHandler)
where TSpecificEventHandler : class
{
List<object> eventHandlerList;
if (!_eventHandlers.TryGetValue(adaptedEventHandler, out eventHandlerList))
{
return null;
}
var eventHandler = eventHandlerList.FirstOrDefault();
if (eventHandler != null)
{
eventHandlerList.Remove(eventHandler);
}
if (!eventHandlerList.Any())
{
_eventHandlers.Remove(adaptedEventHandler);
}
return eventHandler as TSpecificEventHandler;
}
}
This basically remembers in a dictionary the adapted event handler, and the list of SpecificAdaptee's handlers.
So my question: is there a way to adapt events taking ref parameters without retracting to custom delegate type that takes a ref parameter, so I can use standard EventHandler<> class with custom EventArgs descendant?
I realise it's quite a handful of code so please let me know if something is not clear. Thanks in advance.
ref parameter in the event is meant to set from the subscribers. Though it's a bad idea, the api which you're using works based on that.
You can take all the pain in the adapter class and make it work such that consumers are not polluted by the ref parameter. They can continue to use EventArgs style events.
public event EventHandler<AdaptedEventArgs2> AdaptedEvent2
{
add
{
_specificAdaptee.Event2 += _adaptedEventHandlerManager.RegisterEventHandler<AdapteeEventHandler2>(value,
(SpecificAdaptee sender, ref int a) =>
{
var args = new AdaptedEventArgs2 { A = a };
value.Invoke(this, args);
a = args.A;
});
}
remove
{
_specificAdaptee.Event2 -= _adaptedEventHandlerManager.UnregisterEventHandler<AdapteeEventHandler2>(value);
}
}
After the event is executed, we set the value of A to the ref parameter a. This simulates the behavior of ref parameter and also abstracts it under the adapter class. If A is changed in the event handler, it will be reflected in the SpecificAdaptee class too.
To show how this works like a ref parameter:
class SpecificAdaptee
{
...
public void FireEvent2()
{
int a = 42;
if (Event2 != null)
Event2(this, ref a);
Console.WriteLine("A value after the event is {0}", a);
}
}
private static void OnAdaptedEvent2(object sender, AdaptedEventArgs2 args)
{
Console.WriteLine($"{nameof(OnAdaptedEvent2)}({sender}, {args.A})");
args.A = 15;
}
This prints:
A value after the event is 15
PS: For brevity I've added only the parts of your program which needs a change.

Understanding generics and Func arguments

I would not be surprised if this has been answered somewhere, the problem is I am not sure how to phrase a search to find what I need. The things I have already found have either been too simplistic to be usable or poorly explained such that I cannot translate it into my own project. I had no formal instruction with event handlers, delegates, and the like (heck, I didn't even learn about Entity-Component Systems--or other design patterns--until long after I graduated college and was already employed as a programmer, and even then it wasn't something I learned at, or for, my job).
Essentially what I want to know is, what does the definition of Array.Sort<T>(T[] array, Comparison<T> comparison) look like?
There's clearly some kind of generalization going on, as myCompareDelegate(...) takes two arguments of any type. In almost everything I've found relating to Func arguments, a Func<> parameter requires explicitly declared types, with the exception of some sample code using an operator I am unfamiliar with:
SomeUtility(arg => new MyType());
public void SomeUtility<T>(Func<object, T> converter) {
var myType = converter("foo");
}
It compiles but I have no idea what it does and as such, I do not know how to utilize it to create code that will run or do what I want to do.
My goal here is to be able to create an event system (yes, I'm aware that C# has an event system built in, but again, all the sample code I've seen is either simplified to the point of uselessness--listeners contained in the same class as the dispatcher--or complicated and unexplained). I want the following to be true:
a single function to register an event listener (for any Type of event and its subtypes)
a single function to dispatch an event (calling only the relevant listeners)
to be able to create new event types without having to modify the functions for registration and handling (no explicit types in the dispatcher beyond the base event class) provided the new event type extends the allowable event type (i.e. an Entity will only dispatch EntityEvents not WorldEvents).
I have a system that works currently, but it requires that all my handlers pass through a single "onEvent" function which takes a base event object and figures out what it's actual type is, passing that off to the true handler.
Eg:
//Entity implements IEventDispatcher
public SomeConstructor(Entity ent) {
//public delegate void EventListener(EventBase eventData); is declared
//in the IEventDispatcher interface.
ent.attachEvent(typeof(EntityEventPreRender), new EventListener(onEvent));
ent.attachEvent(typeof(EntityEventPostRender), new EventListener(onEvent));
}
//EntityEventPreRender extends EntityEventRender extends EntityEvent extends EventBase
//EntityEventPostRender extends EntityEventRender extends EntityEvent extends EventBase
public void onEvent(EventBase data) {
if(data is EntityEventPreRender)
onPre((EntityEventPreRender)data);
if(data is EntityEventPostRender)
onPost((EntityEventPostRender)data);
}
public void onPre(EntityEventPreRender evt) {}
public void onPost(EntityEventPostRender evt) {}
attachEvent() here is a function that takes a Type (used as a HashMap key) and a Delegate and stores it in a list (the HashMap value). Dispatching the event just needs to pass the EventData object, which is queried for its type (via evt.GetType()) to retrieve the list of listeners, then invoking them: listItem(evt)
But I'd rather be able to just do this:
public SomeConstructor(Entity ent) {
ent.attachEvent(onPre);
ent.attachEvent(onPost);
}
public void onPre(EntityEventPreRender evt) {}
public void onPost(EntityEventPostRender evt) {}
But I cannot, for the life of me, figure out how to do this because I do not know how to declare the attachEvent() function to take a generic function parameter the way Array.Sort<T>(T[] array, Comparison<T> comparison) does. I get the error:
"The type arguments for method doSomething<T>(SomeClass.Thing<T>)' cannot be inferred from the usage. Try specifying the type arguments explicitly."
I think you might be looking for something like the following:
public static class PubSub<TMessage>
{
private static List
<
Action
<
TMessage
>
> listeners = new List<Action<TMessage>>();
public static void Listen(Action<TMessage> listener)
{
if (listener != null) listeners.Add(listener);
}
public static void Unlisten(Action<TMessage> listener)
{
if (listeners.Contains(listener)) listeners.Remove(listener);
}
public static void Broadcast(TMessage message)
{
foreach(var listener in listeners) listener(message);
}
}
In the above code, using PubSub and specifying a type for TMessage creates a new static class in memory with its own memory space allocated for storing a separate list of listeners. The compiler will ensure that only the substituted type for TMessage and its subclasses will be allowed in that list, provided you consistently use the base type as the type argument for the TMessage type parameter.
You would then use it like so:
public class SomeMessageType
{
public int SomeId;
public string SomeDescription;
}
public class SomePublisher
{
public void DoSomethingCool(string description)
{
var randomizer = new Random();
...
PubSub<SomeMessageType>.Broadcast(new SomeMessageType(){SomeId = randomizer.Next(), SomeDescription = description});
}
}
public class SomeListener
{
static SomeListener()
{
PubSub<SomeMessageType>.Listen(SomeMessageEvent);
}
private static void SomeMessageEvent(SomeMessageType message)
{
// do something with the message
}
}
If you then create another class SomeOtherMessageType which does not inherit from SomeMessageType and make similar calls to it, it will only broadcast to listeners of that specific type.
EDITED:
Here is a full proof of concept that compiles that you can run in a console app to allay any remaining concerns you may have over efficacy of this technique.
using System;
using System.Collections.Generic;
namespace TestPubSub
{
public class Program
{
public static void Main(string[] args)
{
Program.startListeners();
Program.sendTestMessages();
Program.stopConsoleFromExitingImmediately();
}
private static void startListeners()
{
SomeListener.Listen();
SomeOtherListener1.Listen();
SomeOtherListener2.Listen();
}
private static void sendTestMessages()
{
var publisher1 = new SomePublisher();
var publisher2 = new SomeOtherPublisher();
publisher1.DoSomethingCool("Hello world");
publisher2.DoSomethingElse(DateTime.Now);
}
private static void stopConsoleFromExitingImmediately()
{
Console.ReadKey();
}
}
public static class PubSub<TMessage>
{
private static List
<
Action
<
TMessage
>
> listeners = new List<Action<TMessage>>();
public static void Listen(Action<TMessage> listener)
{
if (listener != null) listeners.Add(listener);
}
public static void Unlisten(Action<TMessage> listener)
{
if (listeners.Contains(listener)) listeners.Remove(listener);
}
public static void Broadcast(TMessage message)
{
foreach(var listener in listeners) listener(message);
}
}
public class SomeMessageType
{
public int SomeId;
public string SomeDescription;
}
public class SomeOtherMessageType
{
public DateTime SomeDate;
public Double SomeAmount;
}
public class SomePublisher
{
public void DoSomethingCool(string description)
{
var randomizer = new Random();
PubSub<SomeMessageType>.Broadcast(new SomeMessageType(){SomeId = randomizer.Next(), SomeDescription = description});
}
}
public class SomeOtherPublisher
{
public void DoSomethingElse(DateTime when)
{
var randomizer = new Random();
PubSub<SomeOtherMessageType>.Broadcast(new SomeOtherMessageType(){SomeAmount = randomizer.NextDouble(), SomeDate = when});
}
}
public class SomeListener
{
public static void Listen()
{
PubSub<SomeMessageType>.Listen(SomeMessageEvent);
}
private static void SomeMessageEvent(SomeMessageType message)
{
Console.WriteLine("Attention! SomeMessageType receieved by SomeListener with\r\nid: {0}\r\ndescription: {1}\r\n", message.SomeId, message.SomeDescription);
}
}
public class SomeOtherListener1
{
public static void Listen()
{
PubSub<SomeOtherMessageType>.Listen(SomeMessageEvent);
}
private static void SomeMessageEvent(SomeOtherMessageType message)
{
Console.WriteLine("Heads up! SomeOtherMessageType receieved by SomeOtherListener1 with\r\namount: {0}\r\ndate: {1}\r\n", message.SomeAmount, message.SomeDate);
}
}
public class SomeOtherListener2
{
public static void Listen()
{
PubSub<SomeOtherMessageType>.Listen(SomeMessageEvent);
}
private static void SomeMessageEvent(SomeOtherMessageType message)
{
Console.WriteLine("Yo! SomeOtherMessageType receieved by SomeOtherListener2 withr\namount: {0}\r\ndate: {1}\r\n", message.SomeAmount, message.SomeDate);
}
}
}
EDITED AGAIN (Alternate proof of concept using an instance based pubs):
Here is a proof of concept using an instance based PubSub.
using System;
using System.Collections.Generic;
namespace TestPubSub
{
public class Program
{
private static PubSub<SomeMessageType> pubSub1 = new PubSub<SomeMessageType>();
private static PubSub<SomeOtherMessageType> pubSub2 = new PubSub<SomeOtherMessageType>();
private static SomeListener listener1 = new SomeListener();
private static SomeOtherListener1 listener2 = new SomeOtherListener1();
private static SomeOtherListener2 listener3 = new SomeOtherListener2();
public static void Main(string[] args)
{
Program.startListeners();
Program.sendTestMessages();
Program.stopConsoleFromExitingImmediately();
}
private static void startListeners()
{
Program.listener1.Listen(Program.pubSub1);
Program.listener2.Listen(Program.pubSub2);
Program.listener3.Listen(Program.pubSub2);
}
private static void sendTestMessages()
{
var publisher1 = new SomePublisher(Program.pubSub1);
var publisher2 = new SomeOtherPublisher(Program.pubSub2);
publisher1.DoSomethingCool("Hello world");
publisher2.DoSomethingElse(DateTime.Now);
}
private static void stopConsoleFromExitingImmediately()
{
Console.ReadKey();
}
}
public class PubSub<TMessage>
{
private List
<
Action
<
TMessage
>
> listeners = new List<Action<TMessage>>();
public void Listen(Action<TMessage> listener)
{
if (listener != null) this.listeners.Add(listener);
}
public void Unlisten(Action<TMessage> listener)
{
if (listeners.Contains(listener)) this.listeners.Remove(listener);
}
public void Broadcast(TMessage message)
{
foreach(var listener in this.listeners) listener(message);
}
}
public class SomeMessageType
{
public int SomeId;
public string SomeDescription;
}
public class SomeOtherMessageType
{
public DateTime SomeDate;
public Double SomeAmount;
}
public class SomePublisher
{
private PubSub<SomeMessageType> pubSub;
public SomePublisher(PubSub<SomeMessageType> pubSub) { this.pubSub = pubSub; }
public void DoSomethingCool(string description)
{
var randomizer = new Random();
this.pubSub.Broadcast(new SomeMessageType(){SomeId = randomizer.Next(), SomeDescription = description});
}
}
public class SomeOtherPublisher
{
private PubSub<SomeOtherMessageType> pubSub;
public SomeOtherPublisher(PubSub<SomeOtherMessageType> pubSub) { this.pubSub = pubSub; }
public void DoSomethingElse(DateTime when)
{
var randomizer = new Random();
this.pubSub.Broadcast(new SomeOtherMessageType(){SomeAmount = randomizer.NextDouble(), SomeDate = when});
}
}
public class SomeListener
{
public void Listen(PubSub<SomeMessageType> pubSub)
{
pubSub.Listen(this.SomeMessageEvent);
}
private void SomeMessageEvent(SomeMessageType message)
{
Console.WriteLine("Attention! SomeMessageType receieved by SomeListener with\r\nid: {0}\r\ndescription: {1}\r\n", message.SomeId, message.SomeDescription);
}
}
public class SomeOtherListener1
{
public void Listen(PubSub<SomeOtherMessageType> pubSub)
{
pubSub.Listen(this.SomeMessageEvent);
}
private void SomeMessageEvent(SomeOtherMessageType message)
{
Console.WriteLine("Heads up! SomeOtherMessageType receieved by SomeOtherListener1 with\r\namount: {0}\r\ndate: {1}\r\n", message.SomeAmount, message.SomeDate);
}
}
public class SomeOtherListener2
{
public void Listen(PubSub<SomeOtherMessageType> pubSub)
{
pubSub.Listen(this.SomeMessageEvent);
}
private void SomeMessageEvent(SomeOtherMessageType message)
{
Console.WriteLine("Yo! SomeOtherMessageType receieved by SomeOtherListener2 withr\namount: {0}\r\ndate: {1}\r\n", message.SomeAmount, message.SomeDate);
}
}
}

Generics and events

I am making a game and I'm trying to create an way for objects to handle collisions with each other. I want to do something like:
//Imaginary C#
public SomethingThatCollides()
{
CollisionEvent<ObjectA> += CollisionWithObjA;
CollisionEvent<ObjectB> += CollisionWithObjB;
}
void CollisionWithObjA(ObjectA other)
{
//Do something
}
void CollisionWithObjB(ObjectB other)
{
//Do something else
}
When, say, CollisionEvent<ObjectA> is raised (perhaps by some collision checking code), CollisionWithObjA should get called. Same for CollisionWithObjB; when a collision with ObjectB is detected, it will raise the CollisionEvent<ObjectB> event which results in CollisionWithObjB getting called.
Is something like this possible?
Here is the thing, if class is generic and it has static field, it can work like a dictionary with key being type
public class Something {
public class EventsHolder<T>
{
static event Action<T> CollideEvent;
}
public void AddEvent<T>(Action<T> collisionEvent)
{
EventsHolder<T>.CollideEvent = collisionEvent;
}
public void RaiseCollision<T>(T Obj)
{
var Event = EventsHolder<T>.CollideEvent;
if (Event != null) Event(Obj);
}
}
Downside is that it uses static fields which can be inapropriate.
In this case you can use code #Daniel posted.
You can't really create a generic event like that. I suggest you create a special event arguments class that also encapsulates the collided object and check for its type in the event handler method:
public class CollisionEventArgs : EventArgs {
public object Object {
get; private set;
}
// ...
}
You'll need a special dispatcher method to use it:
class SomethingThatCollides {
public SomethingThatCollides(CollisionManager cm) {
cm.CollisionEvent += CollisionWithObj;
}
void CollisionWithObj(object sender, CollisionEventArgs args) {
if (args.Object is ObjectA) {
CollisionWithObjA((ObjectA)args.Object);
}
else if (args.Object is ObjectB) {
CollisionWithObjB((ObjectB)args.Object);
}
}
// ...
}
Or, you can try to solve this with double-dispatching, without using C# events. Look at wikipedia for a collision example.
That's uggly, but...You could have a dicionary of events by type:
Dictionary<Type, object> MyEventsByType;
event Action<A> CollisionEventA;
event Action<B> CollisionEventB;
event Action<C> COllisionEventC;
void Initialize()
{
MyEventsByType = new Dictionary<Type, object>();
MyEventsByType.Add(typeof(A), CollisionEventA);
MyEventsByType.Add(typeof(B), CollisionEventB);
MyEventsByType.Add(typeof(C), CollisionEventC);
}
void RaiseCollision<T>(T Obj)
{
Action<T> Event = (Action<T>)MyEventsByType[typeof(T)];
if (Event != null) Event(Obj);
}

Wrapper for a method that accepts (EventArgs)

I'm trying to implement EventArgs to pass a list of parameters to my messaging system: Question.
I subclassed EventArgs:
public class SingleParameterArgs<T> : EventArgs
{
public T arg1;
public SingleParameterArgs(T _arg1)
{
arg1 = _arg1;
}
}
Here's the class and method that should accept the EventArgs:
static public class Messenger<TEventArgs> where TEventArgs : EventArgs {
private static Dictionary< string, EventHandler<TEventArgs> > eventTable = new Dictionary< string, EventHandler<TEventArgs> >();
static public void Invoke(string eventType, TEventArgs args) {
EventHandler<TEventArgs> eventHandler;
if (eventTable.TryGetValue(eventType, out eventHandler)) {
if (eventHandler != null)
eventHandler();
}
}
}
Before implementing EventArgs I would invoke a message in the following way:
Messenger<GameEndingType>.Invoke( "end game", GameEndingType.TimeEnded );
But now it looks much longer and much more complicated:
Messenger< SingleParameterArgs<GameEndingType> >.Invoke( "end game", new SingleParameterArgs<GameEndingType>(GameEndingType.TimeEnded) );
Is it possible to make it look shorter? I don't want to type such a long line every time I need to send a message. Maybe I could create a wrapper?
Something like this would be perfect:
Messenger.Invoke("end game", GameEndingType.TimeEnded);
What is the best way to create a uniform wrapper for a random amount of parameters?
Are you happy for your Messenger class to be tied to SingleParameterArgs<T>? If so, you could use:
// Here TEventArgs represents the element type *within* SingleParameterArgs
public static class Messenger<TEventArgs> {
private static
Dictionary<string, EventHandler<SingleParameterArgs<TEventArgs>> eventTable =
new Dictionary<string, EventHandler<SingleParameterArgs<TEventArgs>>();
public static void Invoke(string eventType, TEventArgs args) {
EventHandler<SingleParameterArgs<TEventArgs>> eventHandler;
if (eventTable.TryGetValue(eventType, out eventHandler)) {
if (eventHandler != null) {
eventHandler();
}
}
}
}
Of course you can have both, with a totally general Messenger class (as per your question), and then a SingleParameterMessenger class which delegates to it:
public static class SingleParameterMessenger<TEventArgs> {
public static void Invoke(string eventType, TEventArgs args) {
Messenger<SingleParameterArgs<TEventArgs>>.Invoke(eventType, args);
}
}
Just as an aside, I'm not really sure this is all a good idea anyway - particularly in terms of static registration, which tends to make testing harder, and certainly needs more care in terms of concurrency. (Your code is currently not threadsafe.)

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