Messager

This implementation of the event aggregator pattern tries to overcome the limitations of traditional event handling by providing a central place to publish and subscribe for events. It takes care of registering, unregistering and invoking events and thus decoupling publishers and subscribers.

Installation

This package uses Unity's scoped registry feature to import packages and is hosted here. Add the following sections to the package manifest file located in Packages/manifest.json.

Add this object to the scopedRegistries section:

{
  "name": "sov3rain",
  "url": "https://registry.npmjs.com",
  "scopes": [ "com.sov3rain" ]
}

Add this line to the dependencies section:

"com.sov3rain.messager": "1.1.0"

Your manifest file should look like this now:

{
  "scopedRegistries": [{
      "name": "sov3rain",
      "url": "https://registry.npmjs.com",
      "scopes": [ "com.sov3rain" ]
	}],
  "dependencies": {
    "com.sov3rain.messager": "1.1.0",
    ...
  }
}

Usage

Your main access point to the Messager is through its abstraction layer, which uses extension methods. This methods are available from any object by using the this keyword. From here you can access the three primary methods: Listen(), Dispatch() and Cut().

Create a message

Messages are just plain C# objects. They can be classes or structs. They serve the purpose of creating a unique signature by enforcing Type reference instead of string reference.

public struct SIMPLE_MESSAGE
{
    public int Number;
}

Dispatch a message

You can dispatch a new message by using the Dispatch() extension method.

this.Dispatch(new SIMPLE_MESSAGE { Number: 42 });

The message type is inferred by the class instance you pass as an argument.

Start listening for a message

Anywhere in any class, you can listen for a message by using the Listen<T>() extension method. The type you want to listen for is specified through the generic type parameter.

this.Listen<SIMPLE_MESSAGE>(msg => print($"Message incoming: {msg.Number}"));

Note: You can register anonymous functions safely because they are bonded to the instance registering, so they can be removed later.

Stop listening for a message

When you want to stop being notified when a type of message is dispatched, you can call Cut() to unregister the object:

this.Cut<SIMPLE_MESSAGE>();

Note: when using Cut, all listeners registered for that object are removed, as they are referenced by owner. Note 2: remember to always call Cut() before destroying an object instance that is still listening to messages to avoid memory leaks.

Advanced Usage

Referencing the messager

In order to reduce boilerplate code and clutter, Messager comes with extension methods. You can still get a direct reference in any part of your code by accessing the default static instance:

private readonly Messager _messager = Messager.DefaultInstance;

Note: instantiating your own Messager class could help unit testing or mocking, but for regular use, it's recommended to use the default static instance.

private readonly Messenger _myMessager = new Messager();

Then use that specific reference to add you listener and dispatch messages like with extension methods:

// Dispatch
_messager.Dispatch(new SIMPLE_MESSAGE { Number: 42 });

// Listen
_messager.Listen<SIMPLE_MESSAGE>(
    owner: this, 
    handler: msg => print($"Message incoming: {msg.Number}");
);

// Cut
_messager.Cut<SIMPLE_MESSAGE>(this);

Changing the Messager instance

You can change the instance of Messager that will be used by the extension methods by accessing the property Instance like so:

MessagerExtensions.Instance = _myMessager; // Add your custom instance here

Good Practices

DO name your message objects in a ALL_UPPER style to differentiate them from your other classes and structs.

// Bad.
public class SimpleMessage { }

// Good.
public class SIMPLE_MESSAGE { }

DO use immutable objects as messages to avoid side effects:

public sealed class IMMUTABLE_MESSAGE
{
    public int Number { get; }

    public IMMUTABLE_MESSAGE(int number)
    {
        Number = number;
    }
}

public struct IMMUTABLE_STRUCT_MESSAGE
{
    public int Number { get; }

    public IMMUTABLE_STRUCT_MESSAGE(int number)
    {
        Number = number;
    }
}

DO cache the message instance if you plan on reusing it multiple times to avoid unnecessary memory allocations:

var _msg = new SIMPLE_MESSAGE { Number = 42 };

// Example code, don't do that.
void Update()
{
    _messager.Dispatch(this, _msg);
}

Devtools

Messager comes with a set of devtools to let you better track down message subscriptions and have a timed history of published messages. Devtools are never shipped out in build, you can only use them in the Editor.

Enable devtools

By default devtools are disabled. You can toggle them with the menu bar under Messager/Enable Devtools.

Devtools Window

You can open the devtools window with the menu bar under Messager/Open Devtools Window. You can dock the window or use it in floating mode. The window itself has two tabs:

Message history

When you dispatch a message in you application code, a timed record will be created and displayed in the history.

From here you can see the the type of message, the message timecode (from application start). Will be displayed under the foldout the type of the caller and the calling method, and if the message contains data the json serialiazed payload.

You can filter the history by message type. Names are case sensitive.

Subscribers

Available at runtime only, it will show each type of message used and all the subscribers listening to that particular type of message underneath. The number of subscribers will be shown between parentheses. If the subscriber is of type UnityEngine.Object, you will be able to click the object field to select the instance in the scene. If the subscriber is not of type UnityEngine.Object, you will just see the instance type name.

Note: if a message has no subscribers at some point, it will not be shown.

You can also filter the list by message type via the search field. Names are case sensitive.

API Reference

Messager Class

Properties

Name	Description
(Messsager) DefaultInstance	Returns the Messager default instance.

Methods

Name	Description
Use(Middleware onDispatch, Middleware onLister, Middleware onCut)	Initialize middlewares. You can register a delegate matching the following signature: (Type type, object owner, Action next) where next is the next function in the delegate. Devtools use this middlewares to get notified about dispatch, listen and cut.
Listen<T>(object owner, Action<T> handler)	Registers a handler. The type you want to listen for must be passed in the generic parameter.
Cut<T>(object owner)	Remove all handlers owned by the owner object for the specified type.
Dispatch<T>(T payload)	Dispatch a new message. The type can be inferred from the instance passed as the payload parameter.

Messager.Subscription Class

Properties

Name	Description
(object) Owner	The reference of the object owning this message.
(Action<object>) Action	The registered callback. Will be invoked when a new message type matching is dispatched.

Constructors

Name	Description
Subscription(object owner, Action<object> action)	Default constructor. Sets the owner and action properties.