Event/Delegate based Notifications Manager in Unity 3D (10 minute prototype!)

Working backwards (a little anyway, what developer worth his salt doesn’t wander from task to task in a strange order after all!), and with a view to getting a new FPS project up and running as rubber-stamped in my last post, I decided to head towards something I could achieve. Namely, a tidier NotificationsManager class that didn’t rely on using Unity’s in-built object messaging functionality (and its heavy dose of reflection) and instead picked a different approach. You’ve got to do something when a heavy dose of insomnia kicks in!

Based on my own thoughts and a 2 minute trawl online this is what I’ve come up with. This definitely falls into the realm of prototype but I think something along this line could certainly have legs. So without further ado here’s a run-down of the sample project and code I’ve just cooked up, most likely with a view to improve upon once a project gets off the ground.

The game built involves collecting spheres to gain points; 50 points and you win! AAA right there I think you’ll agree! We pull the following components together to form the basic structure/functionality of this game:

  • A GameManager Class (the core class handling central game interactions).
  • A NotificationsManager class (the object responsible for handling events).
  • A PlayerController Class (handling player-centric logic/interactions).
  • A SphereScript Class (simply triggers an event to increment the players score on collision).

The Game World is structured like this:

Game World Configuration.

Game World Configuration.

As with the FPS project I created and reviewed in my previous post, this sample will utilise a core GameManager class. Only one instance of this class will exist per game (I’ve taken steps to ensure this will be a singleton object) and it will ultimately control access to the NotificationsManager directly (for other game objects to call) and handle the game win condition, aka collecting enough spheres. As a cheeky extra, which wouldn’t normally live in this class, a small piece of GUI logic has been added to render the player score in the top left hand corner of the screen.

using UnityEngine;

/// <summary>
/// The core test project GameManager.
/// </summary>
[RequireComponent(typeof(NotificationsManager))]        //A GameManager (when added in the Unity Editor) will automatically attach a NotificationsManager script (if one does not exist)
public class GameManager : MonoBehaviour
{
    #region Private Data Fields

    //A reference to the Player Controller object (on the First Person controller)
    private PlayerController playerCont = null;

    //A cheeky reference to a rectangle (to draw a score on the screen in the OnGUI method)
    private Rect screenRect = new Rect(2.0f, 2.0f, 45.0f, 30.0f);

    #endregion Private Data Fields

    #region Private Static Data Fields

    //Our core, singleton, GameManager instance
    private static GameManager gameManagerInstance = null;
    
    //A singleton instance (accessible through this class) of the NotificationsManager
    private static NotificationsManager notifications = null;

    #endregion Private Static Data Fields

    #region Public Static Properties

    /// <summary>
    /// Global access to a singleton GameManager class (for all game
    /// objects to utilise during play).
    /// </summary>
    public static GameManager GameManagerInstance 
    {
        get
        {
            //Create a new GameObject and add a GameManager script to it if it doesn't already exist (allocating this to the gameManagerInstance field)
            if (gameManagerInstance == null)
            {
                gameManagerInstance = new GameObject("GameManager").AddComponent<GameManager>();
            }

            //Return the instance for global use
            return gameManagerInstance;
        }
    }

    /// <summary>
    /// Global access to a singleton NotificationsManager class (for all game
    /// objects to utilise during play).
    /// </summary>
    public static NotificationsManager Notifications 
    {
        get
        {
            //Set the private notifications field to reference the NotificationsManager script on the GameManagerInstance.
            if (notifications == null)
            {
                notifications = GameManagerInstance.GetComponent<NotificationsManager>();
            }

            //Return the instance for global use
            return notifications;
        }
    }

    #endregion Public Static Properties

    #region Awake/Start

    /// <summary>
    /// In Unity horrific things happen when you use constructors. To that end, 
    /// ensure that only one GameManager comes into existence at game start.
    /// </summary>
    void Awake()
    {
        if (gameManagerInstance != null && gameManagerInstance.GetInstanceID() != GetInstanceID())
        {
            DestroyImmediate(gameObject);
        }
        else
        {
            gameManagerInstance = this;
            DontDestroyOnLoad(gameObject);
        }
    }

    /// <summary>
    /// After Awake, when we've establised one instance of this class for global use, ensure 
    /// that this object has a valid reference to a player object (to read out the score to 
    /// game screen). Register for the OnAllSpheresCollected event.
    /// </summary>
    void Start()
    {
        playerCont = GameObject.FindGameObjectWithTag("Player").GetComponent<PlayerController>();

        //As we've registered for the OnAllSpheresCollected event we don't need to check the player score
        //in the Update method (although we could as we have a PlayerController reference). When a sphere is touched it's 
        //collider will trigger an event picked up in this class (minimising the amount of processing we have to do each frame)
        Notifications.OnAllSpheresCollected += Notifications_OnAllSpheresCollected;
    }

    #endregion Awake/Start

    #region OnGUI

    /// <summary>
    /// Very rudimentary GUI operation. Write 
    /// the player score to the screen.
    /// </summary>
    void OnGUI()
    {
        if (playerCont != null)
        {
            GUI.Label(screenRect, new GUIContent(playerCont.Score.ToString()));
        }
    }

    #endregion OnGUI

    #region Event Handlers

    /// <summary>
    /// Pick up on the NotificationsManager triggering the 
    /// OnAllSpheresCollected event. In this case, this is the 
    /// win condition for the game (simply close and exit).
    /// </summary>
    /// <param name="sender">The component that triggered the event (PlayerController).</param>
    void Notifications_OnAllSpheresCollected(Component sender)
    {
        //We could interrogate the state of the Component here if we needed to (aka the player controller).

#if UNITY_EDITOR
        UnityEditor.EditorApplication.isPlaying = false;
#else
        Application.Quit();
#endif
    }

    #endregion Event Handlers
}

Beforehand, our NotificationsManager maintained a list of strings/components and used the strings (as defined event names) to call the SendMessage method on applicable objects. The GameManager listed above begins to hint at a slightly different approach in this regard. Notice, within the Start method, how an event is being registered (against the NotificationsManager OnAllSpheresCollected event) instead with a handler being exposed within this class; making this class a listener for this event. The Notifications_OnAllSpheresCollected event, which could easily have been an anonymous method (using a lambda expression) has been mocked up to simply end the game.

A NotificationsManager component, as before, is still marked as required and will be added whenever a GameManager script is added to a GameObject within the Unity Editor. Below is an illustration of how the GameManager object is configured in the Unity Editor; showing the scripts added for reference:

Game Manager Configuration.

Game Manager Configuration.

Let’s get into the real beef (not that there is much ‘beef’ in this project, it’s more of a low-fat implementation really!) of the changes made to the NotificationsManager. The tweaked mock-up relies on a single delegate outlining a method that has no return type, which I could expand on later down the line if necessary, and that supports a single argument of type ‘Component’ (most likely another script).

Two public events are then configured to allow objects to register as listeners for the ‘sphere collected’ and ‘all spheres collected’ events. In the first iteration listed here I haven’t given consideration yet to how this should ultimately work (i.e. should these be instance or object level based, aka static – Perhaps even considering the whole class declaration), it’s bare bones. As the NotificationsManager exists as a singleton in the previous project (is instance based), and I only want to prove a concept, having these as non-static and accessible at the instance level works ok for now and allows appropriate access through the GameManager instance.

Finally, two public methods allow objects to ‘post’ notifications to any listening objects, provided the event handler is not null.

using UnityEngine;

/// <summary>
/// Test implementation of a NotificationsManager class
/// using an event/delegate foundation.
/// </summary>
public class NotificationsManager : MonoBehaviour
{
    #region Delegates

    /// <summary>
    /// A delegate representing (outlining) a method that has no return type
    /// and takes a single component as an argument (would have sufficed for the entirety
    /// of the last project I created).
    /// </summary>
    /// <param name="sender">A game component object (a component part of a game object).</param>
    public delegate void ComponentEventHandler (Component sender);

    #endregion Delegates

    #region Component Event Handlers

    /// <summary>
    /// Allows registration for the OnSphereCollected event.
    /// </summary>
    public event ComponentEventHandler OnSphereCollected;

    /// <summary>
    /// Allows registration for the OnAllSpheresCollected
    /// event (essentially our 'win' condition).
    /// </summary>
    public event ComponentEventHandler OnAllSpheresCollected;

    #endregion Component Event Handlers

    #region Public Event Triggers

    /* The meat of the NotificationsManager lies here */

    /// <summary>
    /// Trigger an event on all listeners 
    /// registered with the OnSphereCollected event.
    /// </summary>
    /// <param name="sender">A game component object (a component part of a game object).</param>
    public void SphereCollected(Component sender)
    {
        //Only trigger the event if something is registered
        if (OnSphereCollected != null)
        {
            OnSphereCollected(sender);
        }
    }

    /// <summary>
    /// Trigger an event on all listeners 
    /// registered with the OnAllSpheresCollected event. 
    /// </summary>
    /// <param name="sender">A game component object (a component part of a game object).</param>
    public void AllSpheresCollected(Component sender)
    {
        //Only trigger the event if something is registered
        if (OnAllSpheresCollected != null)
        {
            OnAllSpheresCollected(sender);
        }
    }

    #endregion Public Event Triggers
}

The NotificationsManager is inherently tied to the GameManager and exists on the same GameObject, in the Unity Editor, as the Game Manager.

We’ve started to see the concept of how an event/delegate system could work in Unity for listening/posting objects. The player and sphere objects and associated scripts should hopefully prove the concept in a very basic sense.

Starting with the PlayerController class; the implementation simply allows for a players score to be recorded and the object to be marked as a listener for any object triggering the OnSphereCollected event. This is taken care of by the logic found with the Start initialisation method and the Notifications_OnSphereCollected event handler. The event handler, triggered by a sphere on collision, will just increment the players score by 10 points. If the players score hit 50 points or above then an AllSpheresCollected event can be triggered for all listening objects.

using UnityEngine;

/// <summary>
/// Class representing the player (state, etc).
/// </summary>
public class PlayerController : MonoBehaviour
{
    #region Unity Inspector Public Variables

    /// <summary>
    /// The Players Score. Made public to surface in the 
    /// Unity Editor for fiddling, prevents encapsulation that drives me
    /// a little nuts. Oh well, sigh :o(
    /// </summary>
    public int Score = 0;

    #endregion Unity Inspector Public Variables

    #region Start

    /// <summary>
    /// PlayerController initialistion logic. In this case, simply
    /// register this class as a listener of the OnSphereCollected event
    /// (so we can increment the score and delegate win condition handling to the 
    /// GameManager (as this would likely have more stuff to do, aka further level loading, etc)).
    /// </summary>
    void Start()
    {
        GameManager.Notifications.OnSphereCollected += Notifications_OnSphereCollected; 
    }

    #endregion Start

    #region Event Handlers

    /// <summary>
    /// OnSphereCollected event handler (will be triggered by
    /// a sphere when it's collider comes into contact with the player).
    /// </summary>
    /// <param name="sender"></param>
    void Notifications_OnSphereCollected(Component sender)
    {
        //Debug (check sender object type for reference)
        if (sender != null)
        {
            Debug.Log(sender.GetType());
        }

        //Increment score
        Score += 10;

        //Game won
        if (Score >= 50)
        {
            //It might be more than the GameManager that needs to know about this - This call would take care of all registered objects (listeners)
            GameManager.Notifications.AllSpheresCollected(this);
        }
    }

    #endregion Event Handlers
}

In addition, notice the little bit of debugging listed in the Notifications_OnSphereCollected event handler. We’ll see this in action a little later on. The Player, First Person Controller, GameObject configuration is as follows:

Player Configuration.

Player Configuration.

The last component we need is something that will trigger our NotificationsManager.SphereCollected method; in turn triggering the relevant event to move the game forward (and push the player towards the AllSpheresCollected event that will end the game). The following class definition completes the puzzle.

using UnityEngine;

/// <summary>
/// Class representing Sphere interaction logic.
/// </summary>
public class SphereScript : MonoBehaviour
{
    #region OnTriggerEnter Event

    /// <summary>
    /// OnTriggerEnter event that handles collisions between the object
    /// attached to this script on other colliders.
    /// </summary>
    /// <param name="other">A reference to the colliding object.</param>
    void OnTriggerEnter(Collider other)
    {
        //If this sphere comes into contact with something that isn't the player then return
        if (!other.CompareTag("Player"))
        {
            return;
        }

        //Trigger the sphere collected event and hide this game object
        GameManager.Notifications.SphereCollected(this);
	    gameObject.SetActive(false);
    }

    #endregion OnTriggerEnter Event
}

When a sphere collides with another object the objects tag is inspected. If the object turns out to be the player we can post a notification to the public method found on the NotificationsManager class to trigger the appropriate event (sphere collected) on all listening objects. The final configuration of the sphere GameObject looks like this:

Sphere Configuration.

Sphere Configuration.

Proof is in the pudding so they say so let’s spin the game up and see if we can:

  1. Physically ‘collect’ sphere objects and see the players score increment by 10 points (proving that the OnSphereCollected event is being handled).
  2. Verify that the game ends when the players score is equal to or greater than 50 points (proving that the OnAllSpheresCollected event is being handled).
  3. Verify we receive appropriate debug information during the game.

So, the game fires up and our sphere collecting quest begins!

We’ve toiled hard and finally triumphed; the first sphere has been discovered! Our score is currently 0:

Before sphere 'collection'.

Before sphere ‘collection’.

Let’s pick that sucker up. Walking towards the sphere increments our points score by 10 (and triggers debug information as expected):

After sphere 'collection'.

After sphere ‘collection’.

Collecting 5 spheres, equaling 50 points, ends the game. Hoorah!

I call that a successful test of a 10 minute prototype. I’ve got a strong feeling that, under load, this will definitely perform better than the SendMessage approach and this is still very much open to refinement; given a few hours to think about it I’ll probably overhaul everything. It’s possible to bypass the events entirely and just use raw delegates or setup interface based solutions. However, this seems like a nice step up from the implementation I originally had introduced to me during the previous project.

I’ll definitely plod my way over to Blender shortly and get working on content creation but I’m happy that, given a short amount of time, I can come up with modest solutions to improve upon the backbone components of any proposed game engine I plan to write. I wanted to share the most simple implementation I could think of; this is by no means a complex or definitive example, but I hope it proves a point. If anyone reading does have any suggestions or links to ‘you should do it this way, it’s the best’ documentation or resources then I’d be happy to hear about it.

Signing off!

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