Issues using NotificationCenter to pass value from one object to another

Question

Hi guys,

I'm using NotificationCenter as per the wiki in my game. In it, I have GemPickup.js for gems that get picked up.

 ...
 NotificationCenter.DefaultCenter().PostNotification(this, "AddScore", scoreValue);
 ...

LevelStatus.js manages all the score code, with the member variable "score : int" used for the score.

 ...
 NotificationCenter.DefaultCenter().AddObserver(this, "AddScore");
 ...

The above code is in the Start() function of LevelStatus.js, and the implementation of AddScore() is as follows:


function AddScore(addScore : int)
{
    score += addScore;
}

When the notification is posted, I get the following error in the console:


MissingMethodException: The best match for method AddScore has some invalid parameter.
System.MonoType.InvokeMember (System.String name, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object target, System.Object[] args, System.Reflection.ParameterModifier[] modifiers, System.Globalization.CultureInfo culture, System.String[] namedParameters)
UnityEngine.SetupCoroutine.InvokeMember (System.Object behaviour, System.String name, System.Object variable)
UnityEngine.Component:SendMessage(String, Object, SendMessageOptions)
LevelStatus:LevelStatus$SendMessage$System.String$Notification$UnityEngine.SendMessageOptions(Object, Object[])
UnityScript.Lang.UnityRuntimeServices:Invoke(Object, String, Object[], Type)
NotificationCenter:PostNotification(Notification) (at Assets/Game Logic/NotificationCenter.js:79)
NotificationCenter:PostNotification(Object, String, Object) (at Assets/Game Logic/NotificationCenter.js:61)
GemPickup:OnTriggerEnter(Collider) (at Assets/Props/Scripts/GemPickup.js:26)

Am I using the right approach to pass variables between objects?

MachCUBED

Answer 1

Best Answer

Answer by GuyTidhar · Apr 14, 2012 at 07:32 AM

I think you need to do duck typing (try not to define the type of addScore)

 function AddScore(notification: Notification) 
 { 
    score += notification.data; 
 }

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MachCUBED · Apr 14, 2012 at 03:54 PM 0

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If I don't type it (s per the code you posted), I get the following console error if I try to compile it:


Assets/Game Logic/LevelStatus.js(61,15): BCE0051: Operator '+' cannot be used with a left hand side of type 'int' and a right hand side of type 'Object'.

If I type it as per my original code, the error specified in the original post is a runtime one.

GuyTidhar · Apr 14, 2012 at 05:43 PM 0

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Are you sure you are passing an int?

Cause this compile error does not show on my unity.

MachCUBED · Apr 14, 2012 at 05:48 PM 0

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Yes, I'm passing an int. Here is GemPickup.js in all of its entirety, for the sake of reference:

#pragma strict

var scoreValue : int = 1;

private var target : GameObject;

private var pickedUp = false;

private var levelManager : GameObject;

var pickupSound : AudioClip;

function Start () { target = GameObject.FindGameObjectWithTag("Player"); levelManager = GameObject.FindGameObjectWithTag("LevelManager"); }

function OnTriggerEnter (other : Collider) { // Make it go towards the penguin and disappear pickedUp = true; Debug.Log("Gem collected!");

 Debug.Log("Add score");
 
 //TODO: Add scoring system
 NotificationCenter.DefaultCenter().PostNotification(this, "AddScore", scoreValue);
         
     AudioSource.PlayClipAtPoint(pickupSound, transform.position);
     Destroy(gameObject);

}

scoreValue is an int. It is also the value being passed through to the notification center, as seen in this line:


NotificationCenter.DefaultCenter().PostNotification(this, "AddScore", scoreValue);

Although the documentation for the notification center says any data object can be passed to it, I don't think that's a problem, since the second argument taken by PostNotification() is untyped.

GuyTidhar · Apr 14, 2012 at 05:50 PM 1

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According to the notification center documentation you should do this:

function AddScore(notification: Notification) { score += notification.data; }

where data is the value of what you have passed to the observer.

MachCUBED · Apr 14, 2012 at 06:02 PM 0

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It worked, but only after I turned off #pragma strict in LevelStatus.js. Unfortunately, turning off #pragma strict reduced my framerate by maybe 20%. If I try to compile your last solution with #pragma strict uncommented I get:

Assets/Game Logic/LevelStatus.js(61,15): BCE0051: Operator '+' cannot be used with a left hand side of type 'int' and a right hand side of type 'Object'.

This means that for #pragma strict to work, I need to have it check to see if notification.data is of the datatype int, and bail if it isn't.

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